Laser cooling of mechanical degrees of freedom is one of the most significant achievements in the field of optomechanics. Here, we report, for the first time to the best of our knowledge, efficient passive optomechanical cooling of the motion of a freestanding waveguide coupled to a whispering-gallery-mode (WGM) resonator. The waveguide is an 8 mm long glass-fiber nanospike, which has a fundamental flexural resonance at Ω/2π=2.5 kHz and a Q-factor of 1.2×10^5. Upon launching ∼250 μW laser power at an optical frequency close to the WGM resonant frequency, we observed cooling of the nanospike resonance from room temperature down to 1.8 K. Simultaneous cooling of the first higher-order mechanical mode is also observed. The strong suppression of the overall Brownian motion of the nanospike, observed as an 11.6 dB reduction in its mean square displacement, indicates strong optomechanical stabilization of linear coupling between the nanospike and the cavity mode. The cooling is caused predominantly by a combination of photothermal effects and optical forces between nanospike and WGM resonator. The results are of direct relevance in the many applications of WGM resonators, including atom physics, optomechanics, and sensing.
Iso-entangled mutually unbiased bases, symmetric quantum measurements and mixed-state designs
Jakub Czartowski, Dardo Goyeneche, Markus Grassl, Karol Życzkowski
Physical Review Letters
124(09)
090503
(2020)
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Discrete structures in Hilbert space play a crucial role in finding optimal schemes for quantum measurements. We solve the problem whether a complete set<br>of five iso-entangled mutually unbiased bases exists in dimension four, providing an explicit analytical construction. The reduced density matrices of these 20 pure states forming this generalized quantum measurement form a regular dodecahedron inscribed in a sphere of radius sqrt{3/20} located inside the Bloch ball of radius 1/2. Such a set forms a mixed-state<br>2-design --- a discrete set of quantum states with the property that the mean value of any quadratic function of density matrices is equal to the integral over the entire set of mixed states with respect to the flat Hilbert-Schmidt measure. We establish necessary and sufficient conditions mixed-state designs<br>need to satisfy and present general methods to construct them. Furthermore, it is shown that partial traces of a projective design in a composite Hilbert<br>space form a mixed-state design, while decoherence of elements of a projective design yields a design in the classical probability simplex. We identify a distinguished two-qubit orthogonal basis such that four reduced states are evenly distributed inside the Bloch ball and form a mixed-state 2-design.
Microscale Generation of Entangled Photons without Momentum Conservation
Cameron Okoth, Andrea Cavanna, Tomas Santiago-Cruz, Maria Chekhova
Physical Review Letters
123(26)
263602
(2019)
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We report, for the first time, the observation of spontaneous parametric down-conversion (SPDC) free of phase matching (momentum conservation).We alleviate the need to conserve momentum by exploiting the<br>position-momentum uncertainty relation and using a planar geometry source, a 6 μm thick layer of lithium niobate. Nonphase-matched SPDC opens up a new platform on which to investigate fundamental quantum<br>effects but it also has practical applications. The ultrasmall thickness leads to a frequency spectrum an order of magnitude broader than that of phase-matched SPDC. The strong two-photon correlations are still<br>preserved due to energy conservation. This results in ultrashort temporal correlation widths and huge frequency entanglement. The studies we make here can be considered as the initial steps into the emerging field of nonlinear quantum optics on the microscale and nanoscale.
Formation of optical supramolecular structures in a fibre laser by tailoring long-range soliton interactions
Wenbin He, Meng Pang, Dung-Han Yeh, Jiapeng Huang, Curtis Menyuk, Philip Russell
Self-assembly of fundamental elements through weak, long-range interactions plays a central role in both supramolecular DNA assembly and bottom-up synthesis of nanostructures. Optical solitons, analogous in many ways to particles, arise from the balance between nonlinearity and dispersion and have been studied in numerous optical systems. Although both short- and long-range interactions between optical solitons have attracted extensive interest for decades, stable soliton supramolecules, with multiple aspects of complexity and flexibility, have thus far escaped experimental observation due to the absence of techniques for enhancing and controlling the long-range inter-soliton forces. Here we report that long-range soliton interactions originating from optoacoustic effects and dispersive-wave radiations can be precisely tailored in a fibre laser cavity, enabling self-assembly of large numbers of optical solitons into highly-ordered supramolecular structures. We demonstrate several features of such optical structures, highlighting their potential applications in optical information storage and ultrafast laser-field manipulation.
Field theory of monochromatic optical beams II. Classical and quantum paraxial fields
Andrea Aiello
Journal of Optics
22(1)
014002
(2019)
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This work is the second part of an investigation aiming at the study of optical wave equations from a field-theoretic point of view. Here, we study classical and quantum aspects of scalar fields satisfying the paraxial wave equation. First, we determine conservation laws for energy, linear and angular momentum of paraxial fields in a classical context. Then, we proceed with the quantization of the field. Finally, we compare our result with the traditional ones.
Field theory of monochromatic optical beams I. classical fields
Andrea Aiello
Journal of Optics
22(1)
014001
(2019)
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We study monochromatic, scalar solutions of the Helmholtz and paraxial wave equations from a field-theoretic point of view. We introduce appropriate time-independent Lagrangian densities for which the Euler-Lagrange equations reproduces either Helmholtz and paraxial wave equations with the $z$-coordinate, associated with the main direction of propagation of the fields, playing the same role of time in standard Lagrangian theory. For both Helmholtz and paraxial scalar fields, we calculate the canonical energy-momentum tensor and determine the continuity equations relating ``energy'' and ``momentum'' of the fields. Eventually, the reduction of the Helmholtz wave equation to a useful first-order Dirac form, is presented. This work sheds some light on the intriguing and not so acknowledged connections between angular spectrum representation of optical wavefields, cosmological models and physics of black holes.
Fading channel estimation for free-space continuous-variable secure quantum communication
László Ruppert, Christian Peuntinger, Bettina Heim, Kevin Günthner, Vladyslav C. Usenko, Dominique Elser, Gerd Leuchs, Radim Filip, Christoph Marquardt
New Journal of Physics
21(12)
123036
(2019)
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We investigate estimation of fluctuating channels and its effect on security of continuous-variable quantum key distribution. We propose a novel estimation scheme which is based on the clusterization of the estimated transmittance data. We show that uncertainty about whether the transmittance is fixed or not results in a lower key rate. However, if the total number of measurements is large, one can obtain using our method a key rate similar to the non-fluctuating channel even for highly fluctuating channels. We also verify our theoretical assumptions using experimental data from an atmospheric quantum channel. Our method is therefore promising for secure quantum communication over strongly fluctuating turbulent atmospheric channels.
Detection-device-independent verification of nonclassical light
The efficient certification of nonclassical effects of light forms the basis for applications in optical quantum technologies. We derive general correlation conditions for the verification of nonclassical light based on multiplexed detection. The obtained nonclassicality criteria are valid for imperfectly balanced multiplexing scenarios with on-off detectors and do not require any knowledge about the detector system. In this sense, they are fully independent of the detector system. In our experiment, we study light emitted by clusters of single-photon emitters, whose photon number may exceed the number of detection channels. Even under such conditions, our criteria certify nonclassicality with high statistical significance.
High-yield fabrication of DNA and RNA constructs for single molecule force and torque spectroscopy experiments
Flavia S. Papini, Mona Seifert, David Dulin
Nucleic Acids Research
47(22)
e144
(2019)
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Single molecule biophysics experiments have enabled the observation of biomolecules with a great deal of precision in space and time, e.g. nucleic acids mechanical properties and protein-nucleic acids interactions using force and torque spectroscopy techniques. The success of these experiments strongly depends on the capacity of the researcher to design and fabricate complex nucleic acid structures, as the outcome and the yield of the experiment also strongly depend on the high quality and purity of the final construct. Though the molecular biology techniques involved are well known, the fabrication of nucleic acid constructs for singlemolecule experiments still remains a difficult task. Here, we present new protocols to generate high quality coilable double-stranded DNA and RNA, as well as DNA and RNA hairpins with similar to 500-1000 bp long stems. Importantly, we present a new approach based on single-stranded DNA (ssDNA) annealing and we use magnetic tweezers to show that this approach simplifies the fabrication of complex DNA constructs, such as hairpins, and converts more efficiently the input DNA into construct than the standard PCR-digestion-ligation approach. The protocols we describe here enable the design of a large range of nucleic acid construct for single molecule biophysics experiments.
All fiber polarization insensitive detection for spectrometer based optical coherence tomography using optical switch
David Odeke Otuya, Gargi Sharma, Guillermo J. Tearney, Kanwarpal Singh
OSA Continuum
2(12)
3465-3469
(2019)
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Polarization dependent image artifacts are common in optical coherence tomography imaging. Polarization insensitive detection scheme for swept source based optical coherence tomography systems is well established but is yet to be demonstrated for all fiber spectrometer-based Fourier domain optical coherence tomography systems. In this work, we present an all fiber polarization insensitive detection scheme for spectrometer based optical coherence tomography systems. Images from chicken breast muscle tissue were acquired to demonstrate the effectiveness of this scheme for the conventional Fourier domain optical coherence tomography system.
Quasiprobability currents on the sphere
I. Valtierra, A. B. Klimov, Gerd Leuchs, Luis Sanchez-Soto
We present analytic expressions for the s-parametrized currents on the sphere for both unitary and dissipative evolutions. We examine the spatial distribution of the flow generated by these currents for quadratic Hamiltonians. The results are applied for the study of the quantum dissipative dynamics of the time-honored Kerr and Lipkin models, exploring the appearance of the semiclassical limit in stable, unstable and tunnelling regimes.
Pump-Probe Study of Plasma Dynamics in Gas-Filled Photonic Crystal Fiber Using Counterpropagating Solitons
Mallika Irene Suresh, Felix Köttig, Johannes Köhler, Francesco Tani, Philip Russell
We present a pump-probe technique for monitoring ultrafast polarizability changes. In particular, we use it to measure the plasma density created at the temporal focus of a self-compressing higher-order pump soliton in a gas-filled hollow-core photonic crystal fiber. This is done by monitoring the wavelength of the dispersive wave emission from a counterpropagating probe soliton. By varying the relative delay between pump and probe, the plasma density distribution along the fiber can be mapped out. Compared with recently introduced interferometric side probing for monitoring the plasma density, our technique is relatively immune to instabilities caused by air turbulence and mechanical vibration. The results of two experiments on argon- and krypton-filled fiber are presented and compared to numerical simulations. The technique provides an important tool for probing photoionization in many different gases and gas mixtures, as well as ultrafast changes in dispersion in many other contexts.
Spin-orbit coupling affecting the evolution of transverse spin
Jörg Eismann, Peter Banzer, Martin Neugebauer
Physical Review Research
1(3)
033143-1-033143-4
(2019)
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We investigate the evolution of transverse spin in tightly focused circularly polarized beams of light, where spin-orbit coupling causes a local rotation of the polarization ellipses upon propagation through the focal volume. The effect can be explained as a relative Gouy-phase shift between the circularly polarized transverse field and the longitudinal field carrying orbital angular momentum. The corresponding rotation of the electric transverse spin density is observed experimentally by utilizing a recently developed reconstruction scheme, which relies on transverse-spin-dependent directional scattering of a nano-probe.
Feasibility of quantum key distribution with macroscopically bright coherent light
Olena Kovalenko, Kirill Spasibko, M. V. Chekhova, Vladyslav C. Usenko, Radim Filip
We address feasibility of continuous-variable quantum key distribution using bright multimode coherent states of light and homodyne detection. We experimentally verify the possibility to properly select signal modes by matching them with the local oscillator and this way to decrease the quadrature noise concerned with unmatched bright modes. We apply the results to theoretically predict the performance of continuous-variable quantum key distribution scheme using multimode coherent states in scenarios where modulation is applied either to all the modes or only to the matched ones, and confirm that the protocol is feasible at high overall brightness. Our results open the pathway towards full-scale implementation of quantum key distribution using bright light, thus bringing quantum communication closer to classical optics.
In the recent years a series of experimental and theoretical efforts have centered around a new topic: the coherent, cavity-enhanced interaction between optical photons and solid state magnons. The resulting emerging field of Cavity<br>Optomagnonics is of interest both at a fundamental level, providing a new platform to study light-matter interaction in confined structures, as well as for its possible relevance for hybrid quantum technologies. In this chapter I introduce the basic concepts of Cavity Optomagnonics and review some theoretical developments.
Polyacrylamide Bead Sensors for in vivo Quantification of Cell-Scale Stress in Zebrafish Development
Nicole Träber, Klemens Uhlmann, Salvatore Girardo, Gokul Kesavan, Katrin Wagner, Jens Friedrichs, Ruchi Goswami, K Bai, Michael Brand, et al.
Mechanical stress exerted and experienced by cells during tissue morphogenesis and organ formation plays an important role in embryonic development. While techniques to quantify mechanical stresses in vitro are available, few methods exist for studying stresses in living organisms. Here, we describe and characterize cell-like polyacrylamide (PAAm) bead sensors with well-defined elastic properties and size for in vivo quantification of cell-scale stresses. The beads were injected into developing zebrafish embryos and their deformations were computationally analyzed to delineate spatio-temporal local acting stresses. With this computational analysis-based cell-scale stress sensing (COMPAX) we are able to detect pulsatile pressure propagation in the developing neural rod potentially originating from polarized midline cell divisions and continuous tissue flow. COMPAX is expected to provide novel spatio-temporal insight into developmental processes at the local tissue level and to facilitate quantitative investigation and a better understanding of morphogenetic processes.
Partial optomechanical refrigeration via multi-mode cold-damping feedback
We provide a fully analytical treatment for the partial refrigeration of the thermal motion of a quantum mechanical resonator under the action of feedback. As opposed to standard cavity optomechanics where the aim is to isolate and cool a single mechanical mode, the aim here is to extract the thermal energy from many vibrational modes within a large frequency bandwidth. We consider a standard cold-damping technique, where homodyne readout of the cavity output field is fed into a feedback loop that provides a cooling action directly applied on the mechanical resonator. Analytical and numerical results predict that low final occupancies are achievable independent of the number of modes addressed by the feedback, as long as the cooling rate is smaller than the intermode frequency separation. For resonators exhibiting a few nearly degenerate pairs of modes, cooling is less efficient and a weak dependence on the number of modes is obtained. These scalings hint toward the design of frequency-resolved mechanical resonators, where efficient refrigeration is possible via simultaneous cold-damping feedback.
Sustained Self-Starting Orbital Motion of a Glass-Fiber “Nanoengine” Driven by Photophoretic Forces
Shangran Xie, Riccardo Pennetta, Zheqi Wang, Philip Russell
Controllable optically driven rotation of microscopic objects is desirable in many applications, but is difficult to achieve. Here we report a sustained self-starting orbital motion of a clamped elongated nanostructure, a glass-fiber nanospike, when a CW laser<br>beam is focused axially onto its tip. Analysis shows that photophoretic antitrapping forces,<br>acting on the nanospike with a delayed response, introduce optomechanical gain into the mechanical motion, overcoming the intrinsic mechanical dissipation and resulting in growth from noise of oscillations at the resonant frequency of the nanospike. These photophoretic forces further enable phase-locking of the orthogonal fast and slow vibrations of the nanospike (induced by slight mechanical anisotropy), giving rise to a self-sustained orbital motion. The locked phase of orbital motion can be changed by tuning the gas pressure and adjusting the geometrical asymmetry of the system. This light-driven<br>nanoengine opens up a new degree of freedom for controlling the rotational motion of elongated nano-objects.
Quantum state transfer via acoustic edge states in a 2D optomechanical array
Marc-Antoine Lemonde, Vittorio Peano, Peter Rabl, Dimitris G Angelakis
New Journal of Physics
21
113030
(2019)
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We propose a novel hybrid platform where solid-state spin qubits are coupled to the acoustic modes ofa two-dimensional array of optomechanical(OM)nano cavities. Previous studies of coupled OMcavities have shown that in the presence of strong optical drivingfields, the interplay between thephoton-phonon interaction and their respective inter-cavity hopping allows the generation oftopological phases of sound and light. In particular, the mechanical modes can enter a Chern insulatorphase where the time-reversal symmetry is broken. In this context, we exploit the robust acoustic edgestates as a chiral phononic waveguide and describe a state transfer protocol between spin qubitslocated in distant cavities. We analyze the performance of this protocol as a function of the relevantsystem parameters and show that a high-fidelity and purely unidirectional quantum state transfer canbe implemented under experimentally realistic conditions. As a specific example, we discuss theimplementation of such topological quantum networks in diamond based OM crystals where pointdefects such as silicon-vacancy centers couple to the chiral acoustic channel via strain.
On-the-fly particle metrology in hollow-core photonic crystal fibre
Abhinav Sharma, Shangran Xie, Richard Zeltner, Philip Russell
Optics Express
27(24)
34496-34504
(2019)
Efficient monitoring of airborne particulate matter (PM), especially particles with aerodynamic diameter less than 2.5 µm (PM2.5), is crucial for improving public health. Reliable information on the concentration, size distribution and chemical characteristics of PMs is key to evaluating air pollution and identifying its sources. Standard methods for PM2.5 characterization require sample collection from the atmosphere and post-analysis using sophisticated equipment in a laboratory environment, and are normally very time-consuming. Although optical methods based on analysis of scattering of free-space laser beams or evanescent fields are in principle suitable for real-time particle counting and sizing, lack of knowledge of the refractive index in these methods not only leads to inevitable sizing ambiguity but also prevents identification of the particle material. In the case of evanescent wave detection, the system lifetime is strongly limited by adhesion of particles to the surfaces. Here we report a novel technique for airborne particle metrology based on hollow-core photonic crystal fibre. It offers in situ particle counting, sizing and refractive index measurement with effectively unlimited device lifetime, and relies on optical forces that automatically capture airborne particles in front of the hollow core and propel them into the fibre. The resulting transmission drop, together with the time-of-flight of the particles passing through the fibre, provide unambiguous mapping of particle size and refractive index with high accuracy. The technique offers unique advantages over currently available real-time particle metrology systems, and can be directly applied to monitoring air pollution in the open atmosphere as well as precise particle characterization in a local environment such as a closed room or a reaction vessel.
Highly efficient deep UV generation by four-wave mixing in gas-filled hollow-core photonic crystal fiber
Federico Belli, Amir Abdolvand, John Travers, Philip Russell
We report on a highly efficient experimental scheme for the generation of deep-ultraviolet (UV) ultrashort light pulses using four-wave mixing in gas-filled kagomé-style photonic crystal fiber. By pumping with ultrashort, few microjoule pulses centered at 400 nm, we generate an idler pulse at 266 nm and amplify a seeded signal at 800 nm. We achieve remarkably high pump-to-idler energy conversion efficiencies of up to 38%. Although the pump and seed pulse durations are ∼100 fs, the generated UV spectral bandwidths support sub-15 fs pulses. These can be further extended to support few-cycle pulses. Four-wave mixing in gas-filled hollow-core fibers can be scaled to high average powers and different spectral regions such as the vacuum UV (100–200 nm).
Colloidal crystals of compliant microgel beads to study cell migration and mechanosensitivity in 3D
Katrin Wagner, Salvatore Girardo, Ruchi Goswami, Gonzalo Rosso, Elke Ulbricht, Paul Müller, Despina Soteriou, Nicole Träber, Jochen Guck
Soft Matter
15(47)
9776-9787
(2019)
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Tissues are defined not only by their biochemical composition, but also by their distinct mechanical properties. It is now widely accepted that cells sense their mechanical environment and respond to it. However, studying the effects of mechanics in in vitro 3D environments is challenging since current 3D hydrogel assays convolve mechanics with gel porosity and adhesion. Here, we present novel colloidal crystals as modular 3D scaffolds where these parameters are principally decoupled by using monodisperse, protein-coated PAAm microgel beads as building blocks, so that variable stiffness regions can be achieved within one 3D colloidal crystal. Characterization of the colloidal crystal and oxygen diffusion simulations suggested the suitability of the scaffold to support cell survival and growth. This was confirmed by live-cell imaging and fibroblast culture over a period of four days. Moreover, we demonstrate unambiguous durotactic fibroblast migration and mechanosensitive neurite outgrowth of dorsal root ganglion neurons in 3D. This modular approach of assembling 3D scaffolds from mechanically and biochemically well-defined building blocks allows the spatial patterning of stiffness decoupled from porosity and adhesion sites in principle and provides a platform to investigate mechanosensitivity in 3D environments approximating tissues in vitro.
Measuring the temperature and heating rate of a single ion by imaging
Bharath Srivathsan, Martin Fischer, Lucas Alber, Markus Weber, Markus Sondermann, Gerd Leuchs
New Journal of Physics
21
113014
(2019)
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We present a technique based on high resolution imaging to measure the absolute temperature and the heating rate of a single ion trapped at the focus of a deep parabolic mirror. We collect the fluorescence light scattered by the ion during laser cooling and image it onto a camera. Accounting for the size of the point-spread function and the magnification of the imaging system, we determine the spatial extent of the ion, from which we infer the mean phonon occupation number in the trap. Repeating such measurements and varying the power or the detuning of the cooling laser, we determine the heating rate induced by any kind of effect other than photon scattering. In contrast to other established schemes for measuring the heating rate, the ion is always maintained in a state of thermal equilibrium at temperatures close to the Doppler limit.
CASP1 variants influence subcellular caspase-1 localization, pyroptosome formation, pro-inflammatory cell death and macrophage deformability
Franz Kapplusch, Felix Schulze, Sabrina Rabe-Matschewsky, Susanne Russ, Maik Herbig, Michael Christian Heymann, Katharina Schoepf , Robert Stein, Ursula Range, et al.
CASP1 variants result in reduced enzymatic activity of procaspase-1 and impaired IL-1β release. Despite this, affected individuals can develop systemic autoinflammatory disease. These seemingly contradictory observations have only partially been explained by increased NF-κB activation through prolonged interaction of variant procaspase-1 with RIP2. To identify further disease underlying pathomechanisms, we established an in vitro model using shRNA-directed knock-down of procaspase-1 followed by viral transduction of human monocytes (THP-1) with plasmids encoding for wild-type procaspase-1, disease-associated CASP1 variants (p.L265S, p.R240Q) or a missense mutation in the active center of procaspase-1 (p.C285A). THP1-derived macrophages carrying CASP1 variants exhibited mutation-specific molecular alterations. We here provide in vitro evidence for abnormal pyroptosome formation (p.C285A, p.240Q, p.L265S), impaired nuclear (pro)caspase-1 localization (p.L265S), reduced pro-inflammatory cell death (p.C285A) and changes in macrophage deformability that may contribute to disease pathophysiology of patients with CASP1 variants. This offers previously unknown molecular pathomechanisms in patients with systemic autoinflammatory disease.
Collisional quantum thermometry
Stella Seah, Stefan Nimmrichter, Daniel Grimmer, Jader P. Santos, Valerio Scarini, Gabriel T. Landi
Physical Review Letters
123(18)
180602
(2019)
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We introduce a general framework for thermometry based on collisional models, where ancillas probe thetemperature of the environment through an intermediary system. This allows for the generation of correlatedancillas even if they are initially independent. Using tools from parameter estimation theory, we show through aminimal qubit model that individual ancillas can already outperform the thermal Cramer-Rao bound. In addition,when probed collectively, these ancillas may exhibit superlinear scalings of the Fisher information, especiallyfor weak system-ancilla interactions. Our approach sets forth the notion of metrology in a sequential interactionssetting, and may inspire further advances in quantum thermometry.
Experimental reconstruction of spatial Schmidt modes for a wide-field SU(1,1) interferometer
Gaetano Frascella, Roman V Zakharov, Olga V Tikhonova, Maria Chekhova
We study the spatial mode content at the output of a wide-field SU(1, 1) interferometer, i.e. a nonlinear interferometer comprising two coherently-pumped spatially-multimode optical parametric amplifiers placed in sequence with a focusing element in between. This device is expected to provide a phase sensitivity below the shot-noise limit for multiple modes over<br>a broad angular range. To reconstruct the spatial modes and their weights, we implement<br>a simple method based on the acquisition of only intensity distributions. The eigenmode decomposition of the field is obtained through the measurement of the covariance of intensities at different spatial points. We investigate both the radial and azimuthal (orbital angular momentum) modes and show that their total number is large enough to enable applications of the interferometer in spatially-resolved phase measurements.
Interaction of Axonal Chondrolectin with Collagen XIXa1 Is Necessary for Precise Neuromuscular Junction Formation
Ana-Maria Oprisoreanu, Hannah L. Smith, Sukrat Arya, Richard Webster, Zhen Zhong, Daniel Wehner, Marcos J. Cardozo, Thomas Becker, Kevin Talbot, et al.
Chondrolectin (Chodl) is needed for motor axon extension in zebrafish and is dysregulated in mouse models of spinal muscular atrophy (SMA). However, the mechanistic basis of Chodl function is not known. Here, we use Chodl-deficient zebrafish and mouse mutants to show that the absence of Chodl leads to anatomical and functional defects of the neuromuscular synapse. In zebrafish, the growth of an identified motor axon beyond an "en passant'' synapse and later axon branching from synaptic points are impaired, leading to functional deficits. Mechanistically, motor-neuron-autonomous Chodl function depends on its intracellular domain and on binding muscle-derived collagen XIXa1 by its extracellular C-type lectin domain. Our data support evolutionarily conserved roles of Chodl in synaptogenesis and provide evidence for a "synapse-first'' scenario of motor axon growth in zebrafish.
Cell Mechanics Based Computational Classification of Red Blood Cells Via Unsupervised Machine Intelligence Applied to Morpho-Rheological Markers
Yan Ge, Philipp Rosenddahl, Claudio Duran, Sara Ciucci, Nicole Töpfner, Jochen Guck, Carlo Vittorio Cannistraci
IEEE/ACM Transactions on Computational Biology and Bioinformatics
(2019)
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Despite fluorescent cell-labelling being widely employed in biomedical studies, some of its drawbacks are inevitable, with unsuitable fluorescent probes or probes inducing a functional change being the main limitations. Consequently, the demand for and development of label-free methodologies to classify cells is strong and its impact on precision medicine is relevant. Towards this end, high-throughput techniques for cell mechanical phenotyping have been proposed to get a multidimensional biophysical characterization of single cells. With this motivation, our goal here is to investigate the extent to which an unsupervised machine learning methodology, which is applied exclusively on morpho-rheological markers obtained by real-time deformability and fluorescence cytometry (RT-FDC), can address the difficult task of providing label-free discrimination of reticulocytes from mature red blood cells. We focused on this problem, since the characterization of reticulocytes (their percentage and cellular features) in the blood is vital in multiple human disease conditions, especially bone-marrow disorders such as anemia and leukemia. Our approach reports promising label-free results in the classification of reticulocytes from mature red blood cells, and it represents a step forward in the development of high-throughput morpho-rheological-based methodologies for the computational categorization of single cells. Besides, our methodology can be an alternative but also a complementary method to integrate with existing cell-labelling techniques.<br>
R&D advances for quantum communication systems
Gerd Leuchs, Christoph Marquardt, Luis Sanchez-Soto, Dmitry V. Strekalov, Alan E. Willner
Optical Fiber Telecommunications VII
Chapter 12
495-563
(2019)
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Understanding the nature of light leads to the question of how the principles of quantum physics can be harnessed in practical optical communication. A deeper understanding of fundamental physics has always advanced technology. However, the quantum principles certainly have a distinctly limiting character when looked upon from the engineering point of view. A particle cannot have well-defined momentum and position at the same time. An informative measurement will unpredictably alter the state of a quantum object. One cannot reliably clone an arbitrary quantum state. These and a number of other similar principles give rise to what is commonly known as the quantum “no-go theorems”—a disconcerting term when it comes to building something practical. And yet a search for novel principles of communication enabled by quantum physics began already in its early days and has only intensified since. On this path physicists are faced with a remarkable challenge: to turn a series of negative statements into new technological recipes.
Squeezed vacuum states from a whispering gallery mode resonator
Alexander Otterpohl, Florian Sedlmeir, Ulrich Vogl, Thomas Dirmeier, Golnoush Shafiee, Gerhard Schunk, Dmitry Strekalov, Harald G. L. Schwefel, Tobias Gehring, et al.
Squeezed vacuum states enable optical measurements below the quantum limit and hence are a valuable resource for applications in quantum metrology and also quantum communication. However, most available sources require high pump powers in the milliwatt range and large setups that hinder real-world applications. Furthermore, degenerate operation of such systems presents a challenge. Here, we use a compact crystalline whispering gallery mode resonator made of lithium niobate as a degenerate parametric oscillator. We demonstrate about 1.4 dB noise reduction below the shot-noise level for only 300 μW of pump power in degenerate single-mode operation. Furthermore, we report a record pump threshold as low as 1.35 μW. Our results show that the whispering gallery-based approach presents a promising platform for a compact and efficient source for nonclassical light.
Laser refrigeration of gas filled hollow-core fibres
Christian Sommer, Nicolas Y. Joly, Helmut Ritsch, Claudiu Genes
We evaluate prospects, performance and temperature limits of a new approach to macroscopic scale laser refrigeration. The considered<br>refrigeration device is based on exciplex-mediated frequency up-conversion inside hollow-core fibers pressurized with a dopant - buffer<br>gas mixture. Exciplexes are excited molecular states formed by two atoms (dopant and buffer) which do not form a molecule in the<br>ground state but exhibit bound states for electronically excited states. The cooling cycle consists of absorption of laser photons during<br>atomic collisions inducing light assisted exciplex formation followed by blue-shifted spontaneous emission on the atomic line of the bare<br>dopant atoms after molecular separation. This process, closely related to reversing the gain mechanism in excimer lasers, allows for a large<br>fraction of collision energy to be extracted in each cycle. The hollow-core fiber plays a crucial role as it allows for strong light-matter<br>interactions over a long distance, which maximizes the cooling rate per unit volume and the cooling efficiency per injected photon while<br>limiting re-absorption of spontaneously emitted photons channeled into unguided radiation modes. Using quantum optical rate equations<br>and refined dynamical simulations we derive general conditions for efficient cooling of both the gas and subsequently of the surrounding<br>solid state environment. Our analytical approach is applicable to any specific exciplex system considered and reveals the shape of the<br>exciplex potential landscapes as well as the density of the dopant as crucial tuning knobs. The derived scaling laws allow for the identification<br>of optimal exciplex characteristics that help to choose suitable gas mixtures that maximize the refrigeration efficiency for specific<br>applications.<br>
Full-field characterization of helical Bloch modes guided in twisted coreless photonic crystal fiber
Paul Roth, Gordon Wong, Michael Frosz, Goran Ahmed, Philip Russell
It was recently reported that a photonic crystal fiber (PCF) with no structural core guides light if a permanent chiral twist is introduced by spinning the fiber preform during the draw. The intriguing guidance mechanism behind this novel effect has many remarkable features; for example, it intrinsically supports circularly polarized helical Bloch modes (HBMs) that carry multiple optical vortices, making twisted PCFs of interest in fields such as optical micromanipulation, imaging, quantum optics, and optical communications. Here we report for the first time, to the best of our knowledge, that a twisted coreless PCF supports not just one but a family of guided HBMs, each member of which has a unique transverse field distribution and harmonic spectrum. By making detailed interferometric measurements of the near-field phase and amplitude distributions of HBMs, and expanding them as a series of Bessel beams, we are able to extract the amplitude of each azimuthal and radial HBM harmonic. Good agreement is found with the numerical solutions of Maxwell’s equations. The results shed light on the properties of this curious new optical phenomenon.
Almost thermal operations: inhomogeneous reservoirs
Angeline Shu, Yu Cai, Stella Seah, Stefan Nimmrichter, Valerio Scarini
Physical Review A
100(4)
042107
(2019)
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The resource theory of thermal operations explains the state transformations that are possible ina very specific thermodynamic setting: there is only one thermal bath, auxiliary systems can onlybe in the corresponding thermal state (free states), and the interaction must commute with the freeHamiltonian (free operation). In this paper we study the mildest deviation: the reservoir particlesare subject to inhomogeneities, either in the local temperature (introducing resource states) or inthe local Hamiltonian (generating a resource operation). For small inhomogeneities, the two modelsgenerate the same channel and thus the same state transformations. However, their thermodynamicsis significantly different when it comes to work generation or to the interpretation of the “secondlaws of thermal operations”.
Low cost scalable monolithic common path probe design for the application in endoscopic optical coherence tomography
Katharina Blessing, Shivani Sharma, Alexander Gumann, Kanwarpal Singh
Engineering Research Express
1(2)
025008
(2019)
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Journal
Endoscopic optical coherence tomography is an interference based imaging technique which due to its micron level resolution ability found several applications in medical diagnostics. However, the standard image performance suffers from artefacts caused by dispersion imbalance and polarisation mismatches between reference and sample arm. Such artefacts can be minimised with the use of a special class of probes called common path probes where the reference surface is placed in the vicinity of the sample. Previously reported common path probes suffered from a compromise between sensitivity and resolution. In most cases, proposed probes were not scalable for industrial applications and required sophisticated machines for fabrication, thus limiting their mass production for clinical use. We propose and demonstrate a simple fabrication procedure which would allow small laboratories and industries to mass produce common path probes. Our probe design is based on a thin gold layer within the probe which acts as a reference surface. Low-cost ball lenses were used to focus the signal on the sample. We achieved a sensitivity of 104 dB with the designed probes which is comparable to previously reported common path and non-common path probes. Imaging of biological samples such as pig's oesophagus and pig's coronary artery is also presented.
Carrier-envelope-phase-stable soliton-based pulse compression to 4.4 fs and ultraviolet generation at the 800 kHz repetition rate
Alexey Ermolov, Christian Heide, Philip Dienstbier, Felix Köttig, Francesco Tani, Peter Hommelhoff, Philip Russell
In this Letter, we report the generation of a femtosecond supercontinuum extending from the ultraviolet to the near-infrared spectrum and detection of its carrier-envelope-phase (CEP) variation by f-to-2f interferometry. The spectrum is generated in a gas-filled hollow-core photonic crystal fiber, where soliton dynamics allows the CEP-stable self-compression of the optical parametric chirped-pulse amplifier pump pulses at 800 nm to a duration of 1.7 optical cycles, followed by dispersive wave emission. The source provides up to 1 μJ of pulse energy at the 800 kHz repetition rate, resulting in 0.8 W of average power, and it can be extremely useful, for example in strong-field physics, pump–probe measurements, and ultraviolet frequency comb metrology.
Non-invasive real-time characterization of hollow-core photonic crystal fibers using whispering gallery mode spectroscopy
Michael Frosz, Riccardo Pennetta, Michael Enders, Goran Ahmed, Philip Russell
Single-ring hollow-core photonic crystal fibers, consisting of a ring of one or two thin-walled glass capillaries surrounding a central hollow core, hold great promise for use in optical communications and beam delivery, and are already being successfully exploited for extreme pulse compression and efficient wavelength conversion in gases. However, achieving low loss over long (km) lengths requires highly accurate maintenance of the microstructure—a major fabrication challenge. In certain applications, for example adiabatic mode transformers, it is advantageous to taper the fibers, but no technique exists for measuring the delicate and complex microstructure without first cleaving the taper at several positions along its length. In this Letter, we present a simple non-destructive optical method for measuring the diameter of individual capillaries. Based on recording the spectrum scattered from whispering gallery modes excited in the capillary walls, the technique is highly robust, allowing real-time measurement of fiber structure during the draw with sub-micron accuracy.
Rectification of Bacterial Diffusion in Microfluidic Labyrinths
In nature as well as in the context of infection and medical applications, bacteria often have to move in highly complex environments such as soil or tissues. Previous studies have shown that bacteria strongly interact with their surroundings and are often guided by confinements. Here, we investigate theoretically how the dispersal of swimming bacteria can be augmented by microfluidic environments and validate our theoretical predictions experimentally. We consider a system of bacteria performing the prototypical run-and-tumble motion inside a labyrinth with square lattice geometry. Narrow channels between the square obstacles limit the possibility of bacteria to reorient during tumbling events to an area where channels cross. Thus, by varying the geometry of the lattice it might be possible to control the dispersal of cells. We present a theoretical model quantifying diffusive spreading of a run-and-tumble random walker in a square lattice. Numerical simulations validate our theoretical predictions for the dependence of the diffusion coefficient on the lattice geometry. We show that bacteria moving in square labyrinths exhibit enhanced dispersal as compared to unconfined cells. Importantly, confinement significantly extends the duration of the phase with strongly non-Gaussian diffusion, when the geometry of channels is imprinted in the density profiles of spreading cells. Finally, in good agreement with our theoretical findings, we observe the predicted behaviors in experiments with E. coli bacteria swimming in a square lattice labyrinth created in a microfluidic device. Altogether, our comprehensive understanding of bacterial dispersal in a simple two-dimensional labyrinth makes the first step toward the analysis of more complex geometries relevant for real world applications.
Nonlinear Mach–Zehnder interferometer with ultrabroadband squeezed light
D. B. Horoshko, M. I. Kolobov, F. Gumpert, I. Shand, F. König, M. V. Chekhova
We study both theoretically and experimentally the interference pattern in a nonlinear Mach–Zehnder interferometer formed by two aperiodically-poled crystals, where broadband squeezed light is generated by both crystals via parametric down-conversion with a common quasi- monochromatic pump. This configuration is important for measuring the squeezing produced by the first crystal and also for measuring a small phase shift introduced by a sample between the crystals. On the basis of the approximate quantum Rosenbluth formula for each crystal we develop an ana- lytic model for the field evolution in the interferometer. We report an experimental observation of the interference fringes, caused by the dispersion of the generated PDC waves in both crystals form- ing the interferometer. We observe a displacement of the interference pattern caused by a sample between the crystals and infer the phase shift within a band of 20 nm. The experimental data are in a good agreement with the predictions of the developed model, up to imperfections of the samples.
Towards third-order parametric down-conversion in optical fibers
A. Cavanna, J. Hammer, C. Okoth, R. Ortiz-Ricardo, H. Cruz-Ramirez, K. Garay-Palmett, A. B. U’Ren, M. H. Frosz, X. Jiang, et al.
Optical fibers have been considered an optimal platform for third-order parametric down- conversion since they can potentially overcome the weak third-order nonlinearity by their long interaction length. Here we present, in the first part, a theoretical derivation for the conversion rate both in the case of spontaneous generation and in the presence of a seed beam. Then we review three types of optical fibers and we examine their properties in terms of conversion efficiency and practical feasibility.
Histone H3K27 acetylation precedes active transcription during zebrafish zygotic genome activation as revealed by live-cell analysis
Yuko Sato, Lennart Hilbert, Haruka Oda, Yinan Wan, John M. Heddleston, Teng-Leong Chew, Vasily Zaburdaev, Philipp Keller, Timothee Lionnet, et al.
Development
146 SI(19)
UNSP dev179127
(2019)
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Journal
Histone post-translational modifications are key gene expression regulators, but their rapid dynamics during development remain difficult to capture. We applied a Fab-based live endogenous modification labeling technique to monitor the changes in histone modification levels during zygotic genome activation (ZGA) in living zebrafish embryos. Among various histone modifications, H3 Lys27 acetylation (H3K27ac) exhibited most drastic changes, accumulating in two nuclear foci in the 64- to 1k-cell-stage embryos. The elongating form of RNA polymerase II, which is phosphorylated at Ser2 in heptad repeats within the C-terminal domain (RNAP2 Ser2ph), and miR-430 transcripts were also concentrated in foci closely associated with H3K27ac. When treated with alpha-amanitin to inhibit transcription or JQ-1 to inhibit binding of acetyl-reader proteins, H3K27ac foci still appeared but RNAP2 Ser2ph and miR-430 morpholino were not concentrated in foci, suggesting that H3K27ac precedes active transcription during ZGA. We anticipate that the method presented here could be applied to a variety of developmental processes in any model and non-model organisms.
Optically Addressable Array of Optomechanically Compliant Glass Nanospikes on the Endface of a Soft-Glass Photonic Crystal Fiber
Zheqi Wang, Shangran Xie, Xin Jiang, Fehim Babic, Jiapeng Huang, Riccardo Pennetta, Johannes Köhler, Philip Russell
Arrays of elongated nanoscale structures with suitable optical and mechanical properties can act as probes of numerous physical processes at the nanoscale, with applications in, for example, high-resolution optical imaging and atomic force microscopy. They can also be used to investigate optomechanical phenomena such as synchronization among large assemblies of mechanical oscillators. Here we report a novel and versatile technique for fabricating two-dimensional light-guiding arrays of mechanically compliant glass nanospikes with lengths up to several hundred micrometers. The procedure starts with a multicore fiber made by stacking and drawing capillaries and rods of two different germanate glasses with markedly different acid etching rates. After a suitable etching step, a free-standing nanospike array is created at the fiber endface. The parameters are chosen so that there is evanescent coupling between adjacent nanospikes, which gives rise to strong optomechanical forces that can be exploited to drive and control the mechanical motion of the nanospikes and thus the optical properties.
The standard quantum limit of coherent beam combining
Christian Müller, Florian Sedlmeir, Vitaliy O. Martynov, Christoph Marquardt, Alexey V. Andrianov , Gerd Leuchs
New Journal of Physics
21(9)
093047
(2019)
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Journal
Coherent beam combining refers to the process of generating a bright output beam by merging independent input beams of individually diffusing relative phases by locking them to each other. We report the first quantum mechanical noise limit calculations for coherent beam combining and compare our results to quantum-limited amplification. Our coherent beam combining scheme is based on an optical Fourier transformation which renders the scheme compatible with integrated optics combined with feed-back stabilization of the relative phases. The scheme can be layed out for an arbitrary number of input beams and approaches the shot noise limit for a large number of inputs.
Indefinite-Mean Pareto Photon Distribution from Amplified Quantum Noise
Mathieu Manceau, Kirill Spasibko, Gerd Leuchs, Radim Filip, Maria Chekhova
Extreme events appear in many physics phenomena, whenever the probability distribution has a "heavy tail" differing very much from the equilibrium one. Most unusual are the cases of power-law (Pareto) probability distributions. Among their many manifestations in physics, from "rogue waves" in the ocean to Levy flights in random walks, Pareto dependences can follow very different power laws. For some outstanding cases, the power exponents are less than 2, leading to indefinite values not only for higher moments but also for the mean. Here we present the first evidence of indefinite-mean Pareto distribution of photon numbers at the output of nonlinear effects pumped by parametrically amplified vacuum noise, known as bright squeezed vacuum (BSV). We observe a Pareto distribution with power exponent 1.31 when BSV is used as a pump for supercontinuum generation, and other heavy-tailed distributions (however, with definite moments) when it pumps optical harmonics generation. Unlike in other fields, we can flexibly control the Pareto exponent by changing the experimental parameters. This extremely fluctuating light is interesting for ghost imaging and for quantum thermodynamics as a resource to produce more efficiently nonequilibrium states by single-photon subtraction, the latter of which we demonstrate experimentally.
Wide-field SU(1,1) interferometer
Gaetano Frascella, E. E. Mikhailov, N. Takanashi, R. V. Zakharov, O. V. Tikhonova, Maria Chekhova
An SU(1,1) interferometer uses a sequence of two optical parametric amplifiers for achieving sub-shot-noise sensitivity to a phase shift introduced in between. We present the first realization of a wide-field SU(1,1) interferometer, where the use of a focusing element enables spatially multimode operation within a broad angle. Over this angle, the interference phase is found to be flat. This property is important for the high sensitivity to the phase front disturbance. Further, -4.3 +/- 0.7 dB quadrature squeezing, an essential requirement to the high sensitivity, is experimentally demonstrated for plane-wave modes inside the interferometer. Such an interferometer is useful not only for quantum metrology, but also in remote sensing, enhanced sub-shot-noise imaging, and quantum information processing. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Mechanical changes of peripheral nerve tissue microenvironment and their structural basis during development
Peripheral nerves are constantly exposed to mechanical stresses associated with body growth and limb movements. Although some aspects of these nerves' biomechanical properties are known, the link between nerve biomechanics and tissue microstructures during development is poorly understood. Here, we used atomic force microscopy to comprehensively investigate the elastic modulus of living peripheral nerve tissue cross sections ex vivo at distinct stages of development and correlated these elastic moduli with various cellular and extracellular aspects of the underlying histological microstructure. We found that local nerve tissue stiffness is spatially heterogeneous and evolves biphasically during maturation. Furthermore, we found the intracellular microtubule network and the extracellular matrix collagens type I and type IV as major contributors to the nerves' biomechanical properties, but surprisingly not cellular density and myelin content as previously shown for the central nervous system. Overall, these findings characterize the mechanical microenvironment that surrounds Schwann cells and neurons and will further our understanding of their mechanosensing mechanisms during nerve development. These data also provide the design of artificial nerve scaffolds to promote biomedical nerve regeneration therapies by considering mechanical properties that better reflect the nerve microenvironment.
Accelerated adiabatic quantum gates: optimizing speed versus robustness
Hugo Ribeiro, Aashish A. Clerk
Physical Review A
100(3)
032323
(2019)
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Journal
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We develop new protocols for high-fidelity single qubit gates that exploit and extend theoretical ideas for accelerated adiabatic evolution. Our protocols are compatible with qubit architectures with highly isolated logical states, where traditional approaches are problematic; a prime example are superconducting fluxonium qubits. By using an accelerated adiabatic protocol we can enforce the desired adiabatic evolution while having gate times that are comparable to the inverse adiabatic energy gap (a scale that is ultimately set by the amount of power used in the control pulses). By modelling the effects of decoherence, we explore the tradeoff between speed and robustness that is inherent to shortcuts-to-adiabaticity approaches.
Macroscopicity of quantum mechanical superposition tests via hypothesis falsification
Björn Schrinski, Stefan Nimmrichter, Benjamin A. Stickler, Klaus Hornberger
Physical Review A
100(3)
032111
(2019)
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Journal
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We establish an objective scheme to determine the macroscopicity of quantum mechanical super-position tests, which is based on the Bayesian hypothesis falsification of macrorealistic modificationsof quantum theory. The measure uses the raw data gathered in an experiment, taking into accountall measurement uncertainties, and can be used to directly assess any conceivable quantum test.We determine the resulting macroscopicity for three recent tests of quantum physics: double-wellinterference of Bose-Einstein condensates, Leggett-Garg tests with atomic random walks, and en-tanglement generation and read-out of nanomechanical oscillators.
Targeting Mechanoresponsive Proteins in Pancreatic Cancer: 4-Hydroxyacetophenone Blocks Dissemination and Invasion by Activating MYH14
Alexandra Surcel, Eric S. Schiffhauer, Dustin G. Thomas, Qingfeng Zhu, Kathleen T. DiNapoli, Maik Herbig, Oliver Otto, Hoku West-Foyle, Angela Jacobi, et al.
Cancer Research
79(18)
4665-4678
(2019)
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Journal
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Metastasis is complex, involving multiple genetic, epigenetic, biochemical, and physical changes in the cancer cell and its microenvironment. Cells with metastatic potential are often characterized by altered cellular contractility and deformability, lending them the flexibility to disseminate and navigate through different microenvironments. We demonstrate that mechanoresponsiveness is a hallmark of pancreatic cancer cells. Key mechanoresponsive proteins, those that accumulate in response to mechanical stress, specifically nonmuscle myosin IIA (MYH9) and IIC (MYH14), alpha-actinin 4, and filamin B, were highly expressed in pancreatic cancer as compared with healthy ductal epithelia. Their less responsive sister paralogs-myosin IIB (MYH10), alpha-actinin 1, and filamin A-had lower expression differential or disappeared with cancer progression. We demonstrate that proteins whose cellular contributions are often overlooked because of their low abundance can have profound impact on cell architecture, behavior, and mechanics. Here, the low abundant protein MYH14 promoted metastatic behavior and could be exploited with 4-hydroxyacetophenone (4-HAP), which increased MYH14 assembly, stiffening cells. As a result, 4-HAP decreased dissemination, induced cortical actin belts in spheroids, and slowed retrograde actin flow. 4-HAP also reduced liver metastases in human pancreatic cancer-bearing nude mice. Thus, increasing MYH14 assembly overwhelms the ability of cells to polarize and invade, suggesting targeting the mechanoresponsive proteins of the actin cytoskeleton as a new strategy to improve the survival of patients with pancreatic cancer.<br> Significance: This study demonstrates that mechanoresponsive proteins become upregulated with pancreatic cancer progression and that this system of proteins can be pharmacologically targeted to inhibit the metastatic potential of pancreatic cancer cells.
nanite: using machine learning to assess the quality of atomic force microscopy-enabled nano-indentation data
Paul Müller, Shada Abuhattum Hofemeier, Stephanie Möllmert, Elke Ulbricht, Anna V. Taubenberger, Jochen Guck
BMC Bioinformatics (20)
465
(2019)
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Journal
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Atomic force microscopy (AFM) allows the mechanical characterization of single cells and live tissue by quantifying force-distance (FD) data in nano-indentation experiments. One of the main problems when dealing with biological tissue is the fact that the measured FD curves can be disturbed. These disturbances are caused, for instance, by passive cell movement, adhesive forces between the AFM probe and the cell, or insufficient attachment of the tissue to the supporting cover slide. In practice, the resulting artifacts are easily spotted by an experimenter who then manually sorts out curves before proceeding with data evaluation. However, this manual sorting step becomes increasingly cumbersome for studies that involve numerous measurements or for quantitative imaging based on FD maps.
3D Microenvironment Stiffness Regulates Tumor Spheroid Growth and Mechanics via p21 and ROCK
Anna V. Taubenberger, Salvatore Girardo, Nicole Träber, Elisabeth Fischer-Friedrich, Martin Kräter, Katrin Wagner, Thomas Kurth, Isabel Richter, Barbara Haller, et al.
The mechanical properties of cancer cells and their microenvironment contribute to breast cancer progression. While mechanosensing has been extensively studied using 2D substrates, much less is known about it in a physiologically more relevant 3D context. Here it is demonstrated that breast cancer tumor spheroids, growing in 3D polyethylene glycol-heparin hydrogels, are sensitive to their environment stiffness. During tumor sphe-roid growth, compressive stresses of up to 2 kPa build up, as quantitated using elastic polymer beads as stress sensors. Atomic force microscopy reveals that tumor spheroid stiffness increases with hydrogel stiffness. Also, constituent cell stiffness increases in a Rho associated kinase (ROCK)- and F-actin-dependent manner. Increased hydrogel stiffness correlated with attenuated tumor spheroid growth, a higher proportion of cells in G0/G1 phase, and elevated levels of the cyclin-dependent kinase inhibitor p21. Drug-mediated ROCK inhibition not only reverses cell stiffening upon culture in stiff hydrogels but also increases tumor spheroid growth. Taken together, a mechanism by which the growth of a tumor spheroid can be regulated via cytoskeleton rearrangements in response to its mechanoen-vironment is revealed here. Thus, the findings contribute to a better under-standing of how cancer cells react to compressive stress when growing under confinement in stiff environments.
Route from single-pulse to multi-pulse states in a mid-infrared soliton fiber
laser
Jiapeng Huang, Meng Pang, Xin Jiang, Wenbin He, Philip Russell
State-of-the-art ultrafast mid-IR fiber lasers deliver optical solitons with durations of several hundred femtoseconds. The Er- or Ho-doped fluoride gain fibers generally used in these lasers have strong anomalous dispersion at ∼3 µm, which generally forces them to operate in the soliton regime. Here we report that a pulse-energy clamping effect, caused by the buildup of intracavity nonlinearities, limits the shortest obtainable pulse durations in these mid-infrared soliton fiber lasers. Excessive intra-cavity energy results in soliton instability, collapse and fragmentation into a variety of stable multi-pulse states, including phase-locked soliton molecules and harmonically mode-locked states. We report that the spectral evolution of the mid-IR laser pulses can be recorded between roundtrips through stretching their second-harmonic signal in a 25-km-length of single-mode fiber. Using a modified dispersive Fourier transform set-up, we were able to perform for the first time spectro-temporal measurements of mid-IR laser pulses both in the pulsed state and during pulse collapse and fragmentation. The results provide insight into the complex nonlinear dynamics of mid-IR soliton fiber lasers and open up new opportunities for obtaining a variety of stable multi-pulse mode-locked states at mid-IR wavelengths.
Kommt der künstliche Physiker?
Thomas Fösel, Florian Marquardt, Talitha Weiß
Physik in unserer Zeit
50(5)
220-227
(2019)
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Journal
2016 besiegte das Computerprogramm AlphaGo einen der weltbesten Go‐Spieler. Damit rückte eine technische Revolution ins Bewusstsein der breiten Öffentlichkeit: Selbstlernende künstliche neuronale Netze sind zunehmend in der Lage, Menschen bei bestimmten Aufgaben zu schlagen. Zahlreiche Anwendungen, von der Bilderkennung bis zur automatischen Übersetzung, revolutionieren momentan die Technik – und auch Physik und Astronomie bieten viele potenzielle Einsatzmöglichkeiten. In der Astronomie können neuronale Netze das automatische Klassifizieren von Galaxien übernehmen. In der Statistischen Physik sind Magnetisierungsmuster von ferro‐ oder paramagnetischen Zuständen ein Beispiel. Ein anderes Beispiel ist die Suche nach Quantenfehler‐Korrekturstrategien in zukünftigen Quantencomputern. Unsere Forschung konnte zeigen, dass künstliche neuronale Netze mittels Reinforcement Learning hier bereits eigenständig neue Korrekturstrategien entwickeln können.
Interferometric Scattering (iSCAT) Microscopy & Related Techniques
Richard W. Taylor, Vahid Sandoghdar
Label-Free Super-Resolution Microscopy
25-65
(2019)
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Book Chapter
Interferometric scattering (iSCAT) microscopy is a powerful tool for label-free sensitive detection and imaging of nanoparticles to high spatiotemporal resolution. As it was born out of detection principles central to conventional microscopy, we begin by surveying the historical development of the microscope to examine how the exciting possibility for interferometric scattering microscopy with sensitivities sufficient to observe single molecules has become a reality. We discuss the theory of interferometric detection and also issues relevant to achieving a high detection sensitivity and speed. A showcase of numerous applications and avenues of novel research across various disciplines that iSCAT microscopy has opened up is also presented.
Effects of rigosertib on the osteo-hematopoietic niche in myelodysplastic syndromes
Ekaterina Balaian, Heike Weidner, Manja Wobus, Ulrike Baschant, Angela Jacobi, Anna Mies, Martin Bornhäuser, Jochen Guck, Lorenz C Hofbauer, et al.
Annals of Hematology
98(9)
2063-2072
(2019)
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Journal
Rigosertib is a novel multi-kinase inhibitor, which has clinical activity towards leukemic progenitor cells of patients with high-risk myelodysplastic syndromes (MDS) after failure or progression on hypomethylating agents. Since the bone marrow microenvironment plays an important role in MDS pathogenesis, we investigated the impact of rigosertib on cellular compartments within the osteo-hematopoietic niche. Healthy C57BL/6J mice treated with rigosertib for 3 weeks showed a mild suppression of hematopoiesis (hemoglobin and red blood cells, both - 16%, p < 0.01; white blood cells, - 34%, p < 0.05; platelets, - 38%, p < 0.05), whereas there was no difference in the number of hematopoietic stem cells in the bone marrow. Trabecular bone mass of the spine was reduced by rigosertib (- 16%, p = 0.05). This was accompanied by a lower trabecular number and thickness (- 6% and - 10%, respectively, p < 0.05), partly explained by the increase in osteoclast number and surface (p < 0.01). Milder effects of rigosertib on bone mass were detected in an MDS mouse model system (NHD13). However, rigosertib did not further aggravate MDS-associated cytopenia in NHD13 mice. Finally, we tested the effects of rigosertib on human mesenchymal stromal cells (MSC) in vitro and demonstrated reduced cell viability at nanomolar concentrations. Deterioration of the hematopoietic supportive capacity of MDS-MSC after rigosertib pretreatment demonstrated by decreased number of colony-forming units, especially in the monocytic lineage, further supports the idea of disturbed crosstalk within the osteo-hematopoietic niche mediated by rigosertib. Thus, rigosertib exerts inhibitory effects on the stromal components of the osteo-hematopoietic niche which may explain the dissociation between anti-leukemic activity and the absence of hematological improvement.
Coherent nonlinear optics of quantum emitters in nanophotonic waveguides
Pierre Türschmann, Hanna Le Jeannic, Signe F. Simonsen, Harald Haakh, Stephan Götzinger, Vahid Sandoghdar, Peter Lodahl, Nir Rotenberg
Coherent quantum optics, where the phase of a photon is not scrambled as it interacts with an emitter, lies at the heart of many quantum optical effects and emerging technologies. Solid-state emitters coupled to nanophotonic waveguides are a promising platform for quantum devices, as this element can be integrated into complex photonic chips. Yet, preserving the full coherence properties of the coupled emitter-waveguide system is challenging because of the complex and dynamic electromagnetic landscape found in the solid state. Here, we review progress toward coherent light-matter interactions with solid-state quantum emitters coupled to nanophotonic waveguides. We first lay down the theoretical foundation for coherent and nonlinear light-matter interactions of a two-level system in a quasi-one-dimensional system, and then benchmark experimental realizations. We discuss higher order nonlinearities that arise as a result of the addition of photons of different frequencies, more complex energy level schemes of the emitters, and the coupling of multiple emitters via a shared photonic mode. Throughout, we highlight protocols for applications and novel effects that are based on these coherent interactions, the steps taken toward their realization, and the challenges that remain to be overcome.
Perturbation theory of optical resonances of deformed dielectric spheres
Andrea Aiello, Jack G. E. Harris, Florian Marquardt
Physical Review A
100(2)
023837
(2019)
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Journal
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We analyze the optical resonances of a dielectric sphere whose surface has been slightly deformed in an arbitrary way. Setting up a perturbation series up to second order, we derive both the frequency shifts and modified linewidths. Our theory is applicable, for example, to freely levitated liquid drops or solid spheres, which are deformed by thermal surface vibrations, centrifugal forces or arbitrary surface waves. A dielectric sphere is effectively an open system whose description requires the introduction of non-Hermitian operators characterized by complex eigenvalues and not normalizable eigenfunctions. We avoid these difficulties using the Kapur-Peierls formalism which enables us to extend the popular Rayleigh-Schrödinger perturbation theory to the case of electromagnetic Debye's potentials describing the light fields inside and outside the near-spherical dielectric object. We find analytical formulas, valid within certain limits, for the deformation-induced first- and second-order corrections to the central frequency and bandwidth of a resonance. As an application of our method, we compare our results with preexisting ones finding full agreement.
Non-exponential decay of a giant artificial atom
Gustav Andersson, Baladitya Suri, Lingzhen Guo, Thomas Aref, Per Delsing
In quantum optics, light–matter interaction has conventionally been studied using small atoms interacting with electromagnetic fields with wavelength several orders of magnitude larger than the atomic dimensions1,2. In contrast, here we experimentally demonstrate the vastly different ‘giant atom’ regime, where an artificial atom interacts with acoustic fields with wavelength several orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit3 to surface acoustic waves at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of an atom by attaching it to an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, giving rise to non-Markovian dynamics4. We demonstrate the non-Markovian character of the giant atom in the frequency spectrum as well as non-exponential relaxation in the time domain.
Generation of 1.5 cycle pulses at 780 nm at oscillator repetition rates with stable carrier-envelope phase
Philip Dienstbier, Francesco Tani, Takuya Higuchi, John Travers, Philip Russell, Peter Hommelhoff
We demonstrate a spectral broadening and compression setup for carrier-envelope phase (CEP) stable sub-10-fs Ti:sapphire oscillator pulses resulting in 3.9 fs pulses spectrally centered at 780 nm. Pulses from the oscillator with 2 nJ energy are launched into a 1 mm long all-normal dispersive solid-core photonic crystal fiber and spectrally broadened to more than one octave. Subsequent pulse compression is achieved with a phase-only 4f pulse shaper. Second harmonic frequency resolved optical gating with a ptychographic reconstruction algorithm is used to obtain the spectral phase, which is fed back as a phase mask to the shaper display for pulse compression. The compressed pulses are CEP stable with a long term standard deviation of 0.23 rad for the CEP noise and 0.32 rad for the integrated rms phase jitter. The high total throughput of 15% results in a remaining pulse energy of about 300 pJ at 80 MHz repetition rate. With these parameters and the ability to tailor the spectral phase, the system is well suited for waveform sensitive photoemission experiments with needle tips or nanostructures and can be easily adapted to other sub-10 fs ultra-broadband Ti:sapphire oscillators.
Generation of broadband circularly polarized supercontinuum light in twisted photonic crystal fibers
Rafal Sopalla, Gordon Wong, Nicolas Joly, Michael Frosz, Xin Jiang, Goran Ahmed, Philip Russell
We compare the properties of the broadband supercontinuum (SC) generated in twisted and untwisted solid-core photonic crystal fibers when pumped by circularly polarized<br>40 picosecond laser pulses at 1064 nm. In the helically twisted fiber, fabricated by spinning the preform during the draw, the SC is robustly circularly polarized across its entire<br>spectrum whereas, in the straight fiber, axial fluctuations in linear birefringence and polarization-dependent nonlinear effects cause the polarization state to vary randomly with the wavelength. Theoretical modelling confirms the experimental results. Helically twisted photonic crystal fibers permit the generation of pure circularly polarized SC light with excellent polarization stability against fluctuations in input power and environmental perturbations.
Dynamically Generated Synthetic Electric Fields for Photons
Petr Zapletal, Stefan Walter, Florian Marquardt
Physical Review A
100(2)
023804
(2019)
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Journal
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PDF
Static synthetic magnetic fields give rise to phenomena including the Lorentz force and the quantum Hall effect even for neutral particles, and they have by now been implemented in a variety of physical systems. Moving towards fully dynamical synthetic gauge fields allows, in addition, for backaction of the particles' motion onto the field. If this results in a time-dependent vector potential, conventional electromagnetism predicts the generation of an electric field. Here, we show how synthetic electric fields for photons arise self-consistently due to the nonlinear dynamics in a driven system. Our analysis is based on optomechanical arrays, where dynamical gauge fields arise naturally from phonon-assisted photon tunneling. We study open, one-dimensional arrays, where synthetic magnetic fields are absent. However, we show that synthetic electric fields can be generated dynamically, which, importantly, suppress photon transport in the array. The generation of these fields depends on the direction of photon propagation, leading to a novel mechanism for a photon diode, inducing nonlinear nonreciprocal transport via dynamical synthetic gauge fields.
Interaction of light carrying orbital angular momentum with a chiral dipolar scatterer
Pawel Wozniak, Israel De León, Katja Höflich, Gerd Leuchs, Peter Banzer
The capability to distinguish the handedness of circularly polarized light is a well-known intrinsic property of a chiral nanostructure. It is a long-standing controversial debate, however, whether a chiral object can also sense the vorticity, or the orbital angular momentum (OAM), of a light field. Since OAM is a non-local property, it seems rather counter-intuitive that a point-like chiral object could be able to distinguish the sense of the wave-front of light carrying OAM. Here, we show that a dipolar chiral nanostructure is indeed capable of distinguishing the sign of the phase vortex of the incoming light beam. To this end, we take advantage of the conversion of the sign of OAM, carried by a linearly polarized Laguerre-Gaussian beam, into the sign of optical chirality upon tight focusing. Our study provides for a deeper insight into the discussion of chiral light-matter interactions and the respective role of OAM.
Interferometric Scattering Microscopy: Seeing Single Nanoparticles and Molecules via Rayleigh Scattering
Fluorescence microscopy has been the workhorse for investigating optical phenomena at the nanometer scale but this approach confronts several fundamental limits. As a result, there have been a growing number of activities toward the development of fluorescent-free imaging methods. In this Mini Review, we demonstrate that elastic scattering, the most ubiquitous and oldest optical contrast mechanism, offers excellent opportunities for sensitive detection and imaging of nanoparticles and molecules at very high spatiotemporal resolution. We present interferometric scattering (iSCAT) microscopy as the method of choice, explain its theoretical foundation, discuss its experimental nuances, elaborate on its deep connection to bright-field imaging and other established microscopies, and discuss its promise as well as challenges. A showcase of numerous applications and avenues made possible by iSCAT demonstrates its rapidly growing impact on various disciplines concerned with nanoscopic phenomena.
Nonlinear optics with full three-dimensional illumination
Rojiar Penjweini, Markus Weber, Markus Sondermann, Robert W. Boyd, Gerd Leuchs
Nonlinear optical interactions play a crucial role in modern technology and lead to important applications such as optical switching, optical harmonic generation, and the characterization of ultrafast material processes. Nonlinear interactions are enhanced by using a tightly focused laser beam, but nonetheless they are typically excited by a loosely focused (that is, paraxial) laser beam. Here we investigate a specific process, third-harmonic generation, excited by a highly nonparaxial beam that illuminates an interaction region from a nearly full solid angle. We elucidate the influence of the focal volume and the pump intensity on the number of frequency-tripled photons by varying the solid angle from which the pump light is focused, and we find good agreement between the experiments and numerical calculations. As the pump light is focused to a spot size much smaller than the laser wavelength, the Gouy phase does not limit the yield of frequency-converted photons, in stark contrast to the paraxial regime. We believe that our findings are generic and apply to many other nonlinear optical processes when the pump light is focused from a full solid angle.
High-Throughput Microfluidic Characterization of Erythrocyte Shapes and
Mechanical Variability
Felix Reichel, Johannes Mauer, Ahmad Ahsan Nawaz, Gerhard Gompper, Jochen Guck, Dmitry A. Fedosov
The motion of red blood cells (RBCs) in microchannels is important for microvascular blood flow and biomedical applications such as blood analysis in microfluidics. The current understanding of the complexity of RBC shapes and dynamics in microchannels is mainly based on several simulation studies, but there are a few systematic experimental investigations. Here, we present a combined study that systematically characterizes RBC behavior for a wide range of flow rates and channel sizes. Even though simulations and experiments generally show good agreement, experimental observations demonstrate that there is no single well-defined RBC state for fixed flow conditions but rather a broad distribution of states. This result can be attributed to the inherent variability in RBC mechanical properties, which is confirmed by a model that takes the variation in RBC shear elasticity into account This represents a significant step toward a quantitative connection between RBC behavior in microfluidic devices and their mechanical properties, which is essential for a high-throughput characterization of diseased cells.
Separated Schmidt modes in the angular spectrum of biphotons
N. A. Borshchevskaia, F. Just, K. G. Katamadze, Andrea Cavanna, M. V. Chekhova
We prepared qudits based on angular multimode biphoton states by modulating the pump angular spectrum. The modes were prepared in the Schmidt basis and their intensity distributions did not overlap in space. This allows one to get rid of filtering losses while addressing single modes and to realize a single-shot qudit readout.
Magnon heralding in cavity optomagnonics
Victor A. S. V. Bittencourt, Verena Feulner, Silvia Viola-Kusminskiy
In the emerging field of cavity optomagnonics, photons are coupled coherently to magnons in solid-state systems. These new systems are promising for implementing hybrid quantum technologies. Being able to prepare Fock states in such platforms is an essential step towards the implementation of quantum information schemes. We propose a magnon-heralding protocol to generate a magnon Fock state by detecting an optical cavity photon. Due to the peculiarities of the optomagnonic coupling, the protocol involves two distinct cavity photon modes. Solving the quantum Langevin equations of the coupled system, we show that the temporal scale of the heralding is governed by the magnon-photon cooperativity and derive the requirements for generating high fidelity magnon Fock states. We show that the nonclassical character of the heralded state, which is imprinted in the autocorrelation of an optical “read” mode, is only limited by the magnon lifetime for small enough temperatures. We address the detrimental effects of nonvacuum initial states, showing that high fidelity Fock states can be achieved by actively cooling the system prior to the protocol.
Coherent coupling of single molecules to on-chip ring resonators
Dominik Rattenbacher, Alexey Shkarin, Jan Renger, Tobias Utikal, Stephan Götzinger, Vahid Sandoghdar
We report on cryogenic coupling of organic molecules to ring microresonators obtained by looping subwavelength waveguides (nanoguides). We discuss fabrication and characterization of the chip-based nanophotonic elements which yield a resonator finesse in the order of 20 when covered by molecular crystals. Our observed extinction dips from single molecules reach 22%, consistent with an expected enhancement factor of up to 11 for the molecular emission into the nanoguide. Future efforts will aim at efficient coupling of a handful of molecules via their interaction with a ring microresonator mode, setting the ground for the realization of quantum optical cooperative effects.
Emission of circularly polarized light by a linear dipole
Controlling the polarization state and the propagation direction of photons is a fundamental prerequisite for many nanophotonic devices and a precursor for future on-chip communication, where the emission properties of individual emitters are particularly relevant. Here, we report on the emission of partially circularly polarized photons by a linear dipole. The underlying effect is linked to the near-field part of the angular spectrum of the dipole, and it occurs in any type of linear dipole emitter, ranging from atoms and quantum dots to molecules and dipole-like antennas. We experimentally observe it by near-field to far-field transformation at a planar dielectric interface and numerically demonstrate the utility of this phenomenon by coupling the circularly polarized light to the individual paths of crossing waveguides.
Cavity Quantum Electrodynamics with Frequency-Dependent Reflectors
We present a general framework for cavity quantum electrodynamics with strongly frequency-dependent mirrors. The method is applicable to a variety of reflectors exhibiting sharp internal resonances as can be realized, for example, with photonic-crystal mirrors or with two-dimensional atomic arrays around subradiant points. Our approach is based on a modification of the standard input-output formalism to explicitly include the dynamics of the mirror’s internal resonance. We show how to directly extract the interaction parameters from the comparison with classical transfer matrix theory and how to treat the non-Markovian dynamics of the cavity field mode introduced by the mirror’s internal resonance. As an application within optomechanics, we illustrate how a non-Markovian Fano-resonance cavity with a flexible photonic-crystal mirror can provide both sideband resolution as well as strong heating suppression in optomechanical cooling. This approach, amenable to a wide range of systems, opens up possibilities for using hybrid frequency-dependent reflectors in cavity quantum electrodynamics for engineering novel forms of light-matter interactions.
Vectorial vortex generation and phase singularities upon Brewster reflection
Rene Barczyk, Sergey Nechayev, Muhammad Abdullah Butt, Gerd Leuchs, Peter Banzer
Physical Review A
99(6)
063820
063820-1- 063820-8
(2019)
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We experimentally demonstrate the emergence of a purely azimuthally polarized vectorial vortex beam with a phase singularity upon Brewster reflection of focused circularly polarized light from a dielectric substrate. The effect originates from the polarizing properties of the Fresnel reflection coefficients described in Brewster’s law. An astonishing consequence of this effect is that the reflected<br>field’s Cartesian components acquire local phase singularities at Brewster’s angle. Our observations are crucial for polarization microscopy and open new avenues for the generation of exotic states of light based on spin-to-orbit coupling, without the need for sophisticated optical elements.
Analysis of biomechanical properties of hematopoietic stem and progenitor cells with Real-Time Deformability Cytometry
Angela Jacobi, Philipp Rosendahl, Martin Kräter, Marta Urbanska, Maik Herbig, Jochen Guck
Methods in Molecular Biology
2017
135-148
(2019)
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Book Chapter
Stem cell mechanics, determined predominantly by the cell's cytoskeleton, plays an important role in different biological processes such as stem cell differentiation or migration. Several methods to measure mechanical properties of cells are currently available, but most of them are limited in the ability to screen large heterogeneous populations in a robust and efficient manner-a feature required for successful translational applications. With real-time fluorescence and deformability cytometry (RT-FDC), mechanical properties of cells in suspension can be screened continuously at rates of up to 1,000 cells/s-similar to conventional flow cytometers-which makes it a suitable method not only for basic research but also for a clinical setting. In parallel to mechanical characterization, RT-FDC allows to measure specific molecular markers using standard fluorescence labeling. In this chapter, we provide a detailed protocol for the characterization of hematopoietic stem and progenitor cells (HSPCs) in heterogeneous mobilized peripheral blood using RT-FDC and present a specific morpho-rheological fingerprint of HSPCs that allows to distinguish them from all other blood cell types.
Optical traps and anti-traps for glass nanoplates in hollow waveguides
Mehmet Can Günendi, Shangran Xie, David Novoa, Philip Russell
We study theoretically the optical forces acting on glass nanoplates introduced into<br>hollow waveguides, and show that, depending on the sign of the laser detuning relative to the nanoplate resonance, optomechanical back-action between nanoplate and hollow waveguide can create both traps and anti-traps at intensity nodes and anti-nodes in the supermode field profile, behaving similarly to those experienced by cold atoms when the laser frequency is red or blue detuned of an atomic resonance. This arises from dramatic distortions to the mode profile in the hollow waveguide when the nanoplate is off-resonant, producing gradient forces that vary strongly with nanoplate position. In a planar system, we show that when the nanoplate is constrained by an imaginary mechanical spring, its position exhibits strong bistability as the base position is varied. We then treat a two-dimensional system consisting of an anti-resonant nanoplate in the hollow core of a photonic crystal fiber, and predict the stable dark trapping of nanoplate at core center against both translational and rotational motion. The results show that spatial and angular position of nano-scale objects in hollow waveguides can be optically controlled by launching beams with appropriately synthesized transverse field profiles. <br>
Electrically driven single-photon superradiance from molecular chains in a plasmonic nanocavity
Yang Luo, Gong Chen, Yang Zhang, Li Zhang, Yunjie Yu, Fanfang Kong, Xiaojun Tian, Yao Zhang, Chongxin Shan, et al.
We demonstrate single-photon superradiance from artificially constructed nonbonded zinc-phthalocyanine molecular chains of up to 12 molecules. We excite the system via electron tunneling in a plasmonic nanocavity and quantitatively investigate the interaction of the localized plasmon with single-exciton superradiant states resulting from dipole-dipole coupling. Dumbbell-like patterns obtained by subnanometer resolved spectroscopic imaging disclose the coherent nature of the coupling associated with superradiant states while second-order photon correlation measurements demonstrate single-photon emission. The combination of spatially resolved spectral measurements with theoretical considerations reveals that nanocavity plasmons dramatically modify the linewidth and intensity of emission from the molecular chains, but they do not dictate the intrinsic coherence of the superradiant states. Our studies shed light on the optical properties of molecular collective states and their interaction with nanoscopically localized plasmons.
Reading out Fisher information from the zeros of the point spread function
M. Paúr, B. Stoklasa, D. Koutný, J. Řeháček, Z. Hradil, J. Grover, A. Krzic, Luis Sanchez-Soto
Optics Letters
44(12)
3114-3117
(2019)
We show that, for optical systems whose point spread functions exhibit isolated zeros, the information one can gain about the separation between two incoherent point light sources does not scale quadratically with the separation (which is the distinctive dependence causing Rayleigh’s curse) but only linearly. Moreover, the dominant contribution to the separation information comes from regions in the vicinity of these zeros. We experimentally confirm this idea, demonstrating significant superresolution using natural or artificially created spectral doublets.
Compressed sensing of twisted photons
F. Bouchard, D. Koutny, F. Hufnagel, Z. Hradil, J. Rehacek, Y. S. Teo, D. Ahn, H. Jeong, Luis Sanchez-Soto, et al.
Optics Express
27(13)
17426-17323
(2019)
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The ability to completely characterize the state of a quantum system is an essential element for the emerging quantum technologies. Here, we present a<br>compressed-sensing inspired method to ascertain any rank-deficient qudit state, which we experimentally encode in photonic orbital angular momentum. We efficiently reconstruct these qudit states from a few scans with an intensified CCD camera. Since it requires only a few intensity measurements, our technique<br>would provide an easy and accurate way to identify quantum sources, channels, and systems.
Experimental demonstration of linear and spinning Janus dipoles for polarisation and wavelength selective near-field coupling
M. F. Picardi, Martin Neugebauer, Jörg Eismann, Gerd Leuchs, Peter Banzer, F. J. Rodriguez-Fortuno, A. V. Zayats
The electromagnetic field scattered by nano-objects contains a broad range of wave vectors and can be efficiently coupled to waveguided modes. The dominant ontribution to scattering from subwavelength dielectric and plasmonic nanoparticles is determined by electric and magnetic dipolar<br>responses. Here, we experimentally demonstrate spectral and phase selective excitation of Janus dipoles, sources with electric and magnetic dipoles oscillating out of phase, in order to control near-field interference and directional coupling to waveguides. We show that by controlling the<br>polarisation state of the dipolar excitations and the excitation wavelength to adjust their relative contributions, directionality and coupling strength can be fully tuned. Furthermore, we introduce a novel spinning Janus dipole featuring cylindrical symmetry in the near and far field, which results in either omnidirectional coupling or noncoupling. Controlling the propagation of guided light waves via fast and robust near-field <br> interference between polarisation components of a source is required in many applications in nanophotonics and quantum optics.
Mimicking Chiral Light-Matter Interaction
Sergey Nechayev, Peter Banzer
Physical Review B
99(24)
241101(R)
241101-1- 241101-6
(2019)
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Journal
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We demonstrate that electric-dipole scatterers can mimic chiral light-matter interaction by generating far-field circular polarization upon scattering, even though the optical chirality of the incident field as well as that of the scattered light is zero. The presented effect originates from the fact that electric-dipole scatterers respond selectively only to the incident electric field, which eventually results in depolarization of the transmitted beam and in generation of far-field circular polarization. To experimentally demonstrate this effect we utilize a cylindrical vector beam with spiral polarization and a spherical gold nanoparticle positioned on the optical axis -- the axis of rotational symmetry of the system. Our experiment and a simple theoretical model address the fundamentals of duality symmetry in optics and chiral light-matter interactions, accentuating their richness and ubiquity yet in highly symmetric configurations.
Resonance inversion in a superconducting cavity coupled to artificial atoms and a microwave background
Juha Leppäkangas, Jan David Brehm, Ping Yang, Lingzhen Guo, Michael Marthaler, Alexey V. Ustinov, Martin Weides
Physical Review A
99(6)
063804
(2019)
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We demonstrate how heating of an environment can invert the line shape of a driven cavity. We consider a superconducting coplanar cavity coupled to multiple artificial atoms. The measured cavity transmission is characterized by Fano-type resonances with a shape that is continuously tunable by bias current through nearby (magnetic flux) control lines. In particular, the same dispersive shift of the microwave cavity can be observed as a peak or a dip. We find that this Fano-peak inversion is possible due to a tunable interference between a microwave transmission through a background, with reactive and dissipative properties, and through the cavity, affected by bias-current induced heating. The background transmission occurs due to crosstalk with the multiple control lines. We show how such background can be accounted for by a Jaynes- or Tavis-Cummings model with modified boundary conditions between the cavity and transmission-line microwave fields. A dip emerges when cavity transmission is comparable with background transmission and dissipation. We find generally that resonance positions determine system energy levels, whereas resonance shapes give information on system fluctuations and dissipation.
MRI-guided robotic arm drives optogenetic fMRI with concurrent Ca2+ recording
Y Chen, P Pais-Roldán, X Chen, Michael Frosz, X Yu
Optical fiber-mediated optogenetic activation and neuronal Ca2+ recording in combination with fMRI provide a multi-modal fMRI platform. Here, we developed an MRI-guided robotic arm (MgRA) as a flexible positioning system with high precision to real-time assist optical fiber brain intervention for multi-modal animal fMRI. Besides the ex vivo precision evaluation, we present the highly reliable brain activity patterns in the projected basal forebrain regions upon MgRA-driven optogenetic stimulation in the lateral hypothalamus. Also, we show the step-wise optical fiber targeting thalamic nuclei and map the region-specific functional connectivity with whole-brain fMRI accompanied by simultaneous calcium recordings to specify its circuit-specificity. The MgRA also guides the real-time microinjection to specific deep brain nuclei, which is demonstrated by an Mn-enhanced MRI method. The MgRA represents a clear advantage over the standard stereotaxic-based fiber implantation and opens a broad avenue to investigate the circuit-specific functional brain mapping with the multi-modal fMRI platform.
Thresholdless deep and vacuum ultraviolet Raman frequency conversion in hydrogen-filled photonic crystal fiber
Manoj K. Mridha, David Novoa, Pooria Hosseini, Philip St. J. Russell
Coherent ultraviolet light has many uses, for example, in the study of molecular species relevant in biology and chemistry. Very few, if any, laser materials offer ultraviolet transparency along with damage-free operation at high-photon energies and laser power. Here we report efficient generation of narrowband deep and vacuum ultraviolet light using hydrogen-filled hollow-core photonic crystal fiber. Pumping above the stimulated Raman threshold at 532 nm, coherent molecular vibrations are excited in the gas, permitting thresholdless wavelength conversion in the ultraviolet with efficiencies close to 60%. The system is uniquely pressure tunable, allows spatial structuring of the out-coupled radiation, and shows excellent performance in the vacuum ultraviolet. As the underlying scattering process is effectively linear, our approach can also in principle operate at the single-photon level, when all other alternatives are extremely inefficient.
Fabrication and non-destructive characterization of tapered single-ring hollow-core photonic crystal fiber
Riccardo Pennetta, Michael T. Enders, Michael H. Frosz, Francesco Tani, Philip St. J. Russell
We report on the properties of tapered single-ring hollow-core photonic-crystal fibers, with a particular emphasis on applications in nonlinear optics. The simplicity of these structures allows the use of non-invasive side-illumination to assess the quality of the tapering process, by<br>observing the scattered far-field spectrum originating from excitation of whispering-gallery modes in the cladding capillaries. We investigate the conditions that ensure adiabatic propagation in the up- and down-tapers, and the scaling of loss-bands (created by anti-crossings between the core mode and modes in the capillary walls) with taper ratio. We also present an analytical model for the pressure profile along a tapered hollow fiber under differential pumping
Langevin Approach to Quantum Optics with Molecules
We investigate the interaction between light and molecular systems modeled as quantum emitters coupled to a multitude of vibrational modes via a Holstein-type interaction. We follow a quantum Langevin equations approach that allows for analytical derivations of absorption and fluorescence profiles of molecules driven by classical fields or coupled to quantized optical modes. We retrieve analytical expressions for the modification of the radiative emission branching ratio in the Purcell regime and for the asymmetric cavity transmission associated with dissipative cross talk between upper and lower polaritons in the strong coupling regime. We also characterize the Förster resonance energy transfer process between donor-acceptor molecules mediated by the vacuum or by a cavity mode.
Morpho-Rheological Fingerprinting of Rod Photoreceptors Using Real-Time Deformability Cytometry
Tiago Santos-Ferreira, Maik Herbig, Oliver Otto, Madalena Carido, Mike O. Karl, Stylianos Michalakis, Jochen Guck, Marius Ader
Cytometry A
95(11)
1145-1157
(2019)
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Distinct cell-types within the retina are mainly specified by morphological and molecular parameters, however, physical properties are increasingly recognized as a valuable tool to characterize and distinguish cells in diverse tissues. High-throughput analysis of morpho-rheological features has recently been introduced using real-time deformability cytometry (RT-DC) providing new insights into the properties of different cell-types. Rod photoreceptors represent the main light sensing cells in the mouse retina that during development forms apically the densely packed outer nuclear layer. Currently, enrichment and isolation of photoreceptors from retinal primary tissue or pluripotent stem cell-derived organoids for analysis, molecular profiling, or transplantation is achieved using flow cytometry or magnetic activated cell sorting approaches. However, such purification methods require genetic modification or identification of cell surface binding antibody panels. Using primary retina and embryonic stem cell-derived retinal organoids, we characterized the inherent morpho-mechanical properties of mouse rod photoreceptors during development based on RT-DC. We demonstrate that rods become smaller and more compliant throughout development and that these features are suitable to distinguish rods within heterogenous retinal tissues. Hence, physical properties should be considered as additional factors that might affect photoreceptor differentiation and retinal development besides representing potential parameters for label-free sorting of photoreceptors.
Large-Area 3D Plasmonic Crescents with Tunable Chirality
Eric S. A. Goerlitzer, Reza Mohammadi, Sergey Nechayev, Peter Banzer, Nicolas Vogel
Abstract Chiral plasmonic nanostructures hold promise for enhanced chiral sensing and circular dichroism spectroscopy of chiral molecules. It is therefore of interest to fabricate chiral plasmonic nanostructures with tailored chiroptical properties over large areas with reasonable effort. Here, a colloidal lithography approach is used to produce macroscopic arrays of sub-micrometer 3D chiral plasmonic crescent structures over areas >1 cm2. The chirality originates from symmetry breaking by the introduction of a step within the crescent structure. This step is produced by an intermediate layer of silicon dioxide onto which the metal crescent structure is deposited. It is experimentally demonstrated that the chiroptical properties in such structures can be tailored by changing the position of the step within the crescent. These experiments are complemented by finite element simulations and the application of a multipole expansion to elucidate the physical origin of the circular dichroism of the crescent structures.
Pump-probe multi-species CARS in a hollow-core PCF with a 20 ppm detection limit under ambient conditions
Rinat Tyumenev, Luisa Späth, Barbara M. Trabold, Goran Ahmed, Michael H. Frosz, Philip St. J. Russell
We report coherent anti-Stokes Raman spectroscopy (CARS) in a gas-filled single-ring hollow-core photonic crystal fiber (SR-PCF) using a pump-probe configuration. The long collinear path length offered by an SR-PCF strongly enhances the efficiency of the Raman interactions. Pressure tuning the zero-dispersion wavelength (ZDW) of the SR-PCF allows the Raman coherence prepared by seeded pumping at 515 nm to be used in the visible for phase-matched generation of an anti-Stokes signal from a probe in the ultraviolet. The unique dispersion profile in the vicinity of the ZDW enables simultaneous phase matching of all known Raman transitions. We demonstrate that simultaneous multi-species CARS with a detection limit of 20 ppm is possible with only 20 kW of peak pump power delivered by a single laser source.
Multi-twist polarization ribbon topologies in highly-confined optical fields
Thomas Bauer, Peter Banzer, Frédéric Bouchard, Sergej Orlov, Lorenzo Marrucci, Enrico Santamato, Robert W Boyd, Ebrahim Karimi, Gerd Leuchs
New Journal of Physics
21
053020
(2019)
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Electromagnetic plane waves, solutions to Maxwell's equations, are said to be 'transverse' in vacuum. Namely, the waves' oscillatory electric and magnetic fields are confined within a plane transverse to the waves' propagation direction. Under tight-focusing conditions however, the field can exhibit longitudinal electric or magnetic components, transverse spin angular momentum, or non-trivial topologies such as Möbius strips. Here, we show that when a suitably spatially structured beam is tightly focused, a 3-dimensional polarization topology in the form of a ribbon with two full twists appears in the focal volume. We study experimentally the stability and dynamics of the observed polarization ribbon by exploring its topological structure for various radii upon focusing and for different propagation planes.
Substrate-Induced Chirality in an Individual Nanostructure
Sergey Nechayev, Rene Barczyk, Uwe Mick, Peter Banzer
We experimentally investigate the chiral optical response of an individual nanostructure consisting of three equally sized spherical nanoparticles made of different materials and arranged in \ang{90} bent geometry. Placing the nanostructure on a substrate converts its morphology from achiral to chiral. Chirality leads to pronounced differential extinction, i.e., circular dichroism and optical rotation, or equivalently, circular birefringence, which would be strictly forbidden in the absence of a substrate or heterogeneity. This first experimental observation of the substrate-induced break of symmetry in an individual heterogeneous nanostructure sheds new light on chiral light-matter interactions at substrate-nanostructure interfaces.
Spatio-temporal measurement of ionization-induced modal index changes in gas-filled PCF by prism-assisted side-coupling
Barbara M. Trabold, Mallika I. Suresh, Johannes R. Köhler, Michael H. Frosz, Francesco Tani, Philip St. J. Russell
We report the use of prism-assisted side-coupling to investigate the spatio-temporal dynamics of photoionization in an Ar-filled hollow-core photonic crystal fiber. By launching four different LP core modes we are able to probe temporal and spatial changes in the modal refractive index on timescales from a few hundred picoseconds to several hundred microseconds after the ionization event. We experimentally analyze the underlying gas density waves and find good agreement with quantitative and qualitative hydrodynamic predictions. Moreover, we observe periodic modulations in the MHz-range lasting for a few microseconds, indicating nanometer-scale vibrations of the fiber structure, driven by gas density waves.
Investigating the Optical Properties of a Laser Induced 3D Self‐Assembled Carbon–Metal Hybrid Structure
Muhammad Abdullah Butt, Antonino Calà Lesina, Martin Neugebauer, Thomas Bauer, Lora Ramunno, Alessandro Vaccari, Pierre Berini, Yuriy Petrov, Denis Danilov, et al.
Small
15(18)
1900512
1900512-1-1900512-9
(2019)
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Journal
Carbon‐based and carbon–metal hybrid materials hold great potential for applications in optics and electronics. Here, a novel material made of carbon and gold–silver nanoparticles is discussed, fabricated using a laser‐induced self‐assembly process. This self‐assembled metamaterial manifests itself in the form of cuboids with lateral dimensions on the order of several micrometers and a height of tens to hundreds of nanometers. The carbon atoms are arranged following an orthorhombic unit cell, with alloy nanoparticles intercalated in the crystalline carbon matrix. The optical properties of this metamaterial are analyzed experimentally using a microscopic Müller matrix measurement approach and reveal a high linear birefringence across the visible spectral range. Theoretical modeling based on local‐field theory applied to the carbon matrix links the birefringence to the orthorhombic unit cell, while finite‐difference time‐domain simulations of the metamaterial relates the observed optical response to the distribution of the alloy nanoparticles and the optical density of the carbon matrix.
How bacterial cells and colonies move on solid substrates
Wolfram Poenisch, Christoph A. Weber, Vasily Zaburdaev
Many bacteria rely on active cell appendages, such as type IV pili, to move over substrates and interact with neighboring cells. Here, we study the motion of individual cells and bacterial colonies, mediated by the collective interactions of multiple pili. It was shown experimentally that the substrate motility of Neisseria gonorrhoeae cells can be described as a persistent random walk with a persistence length that exceeds the mean pili length. Moreover, the persistence length increases for a higher number of pili per cell. With the help of a simple, tractable stochastic model, we test whether a tug of war without directional memory can explain the persistent motion of single Neisseria gonorrhoeae cells. While persistent motion of single cells indeed emerges naturally in the model, a tug of war alone is not capable of explaining the motility of microcolonies, which becomes weaker with increasing colony size. We suggest sliding friction between the microcolonies and the substrate as the missing ingredient. While such friction almost does not affect the general mechanism of single cell motility, it has a strong effect on colony motility. We validate the theoretical predictions by using a three-dimensional computational model that includes explicit details of the pili dynamics, force generation, and geometry of cells.
Enhanced collective Purcell effect of coupled quantum emitter systems
David Plankensteiner, Christian Sommer, Michael Reitz, Helmut Ritsch, Claudiu Genes
Cavity-embedded quantum emitters show strong modifications of free space radiation properties such as an enhanced decay known as the Purcell effect. The central parameter is the cooperativity C - the ratio of the square of the coherent cavity coupling strength over the product of cavity and emitter decay rates. For a single emitter, C is independent of the transition dipole moment and dictated by geometric cavity properties such as finesse and mode waist. In a recent work Phys. Rev. Lett. 119, 093601 (2017) we have shown that collective excitations in ensembles of dipole-dipole coupled quantum emitters show a disentanglement between the coherent coupling to the cavity mode and spontaneous free space decay. This leads to a strong enhancement of the cavity cooperativity around certain collective subradiant antiresonances. Here, we present a quantum Langevin equations approach aimed at providing results beyond the classical coupled dipoles model. We show that the subradiantly enhanced cooperativity imprints its effects onto the cavity output field quantum correlations while also strongly increasing the cavity-emitter system's collective Kerr nonlinear effect.
Coherently refreshed acoustic phonons for extended light storage
Birgit Stiller, Moritz Merklein, Christian Wolff, Khu Vu, Pan Ma, Stephen J. Madden, Benjamin J. Eggleton
Acoustic waves can serve as memory for optical information, however, acoustic phonons in the GHz regime decay on the nanosecond timescale. Usually this is dominated by intrinsic acoustic loss due to inelastic scattering of the acoustic waves and thermal phonons. Here we show a way to counteract the intrinsic acoustic decay of the phonons in a waveguide by resonantly reinforcing the acoustic wave via synchronized optical pulses. This scheme overcomes the previous constraints of phonon-based optical signal processing for light storage and memory. We experimentally demonstrate on-chip storage up to 40 ns, four times the intrinsic acoustic lifetime in the waveguide. We confirm the coherence of the scheme by detecting the phase of the delayed optical signal after 40 ns using homodyne detection. Through theoretical considerations we anticipate that this concept allows for storage times up to microseconds within realistic experimental limitations while maintaining a GHz bandwidth of the optical signal. The refreshed phonon-based light storage removes the usual bandwidth-delay product limitations of e.g. slow-light schemes.
Nanoprinting organic molecules at the quantum level
Claudio U. Hail, Christian Höller, Korenobu Matsuzaki, Patrik Rohner, Jan Renger, Vahid Sandoghdar, Dimos Poulikakos, Hadi Eghlidi
Organic compounds present a powerful platform for nanotechnological applications. In particular, molecules suitable for optical functionalities such as single photon generation and energy transfer have great promise for complex nanophotonic circuitry due to their large variety of spectral properties, efficient absorption and emission, and ease of synthesis. Optimal integration, however, calls for control over position and orientation of individual molecules. While various methods have been explored for reaching this regime in the past, none satisfies requirements necessary for practical applications. Here, we present direct non-contact electrohydrodynamic nanoprinting of a countable number of photostable and oriented molecules in a nanocrystal host with subwavelength positioning accuracy. We demonstrate the power of our approach by writing arbitrary patterns and controlled coupling of single molecules to the near field of optical nanostructures. Placement precision, high yield and fabrication facility of our method open many doors for the realization of novel nanophotonic devices.
Spheroid Culture of Mesenchymal Stromal Cells Results in Morphorheological Properties Appropriate for Improved Microcirculation
Stefanie Tietze, Martin Kräter, Angela Jacobi, Anna Taubenberger, Maik Herbig, Rebekka Wehner, Marc Schmitz, Oliver Otto, Catrin List, et al.
Advanced Science
6(8)
1802104
(2019)
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Human bone marrow mesenchymal stromal cells (MSCs) are used in clinical trials for the treatment of systemic inflammatory diseases due to their regenerative and immunomodulatory properties. However, intravenous administration of MSCs is hampered by cell trapping within the pulmonary capillary networks. Here, it is hypothesized that traditional 2D plastic-adherent cell expansion fails to result in appropriate morphorheological properties required for successful cell circulation. To address this issue, a method to culture MSCs in nonadherent 3D spheroids (mesenspheres is adapted. The biological properties of mesensphere-cultured MSCs remain identical to conventional 2D cultures. However, morphorheological analyses reveal a smaller size and lower stiffness of mesensphere-derived MSCs compared to plastic-adherent MSCs, measured using real-time deformability cytometry and atomic force microscopy. These properties result in an increased ability to pass through microconstrictions in an ex vivo microcirculation assay. This ability is confirmed in vivo by comparison of cell accumulation in various organ capillary networks after intravenous injection of both types of MSCs in mouse. The findings generally identify cellular morphorheological properties as attractive targets for improving microcirculation and specifically suggest mesensphere culture as a promising approach for optimized MSC-based therapies.
Interferometric scattering microscopy reveals microsecond nanoscopic protein motion on a live cell membrane
Richard W. Taylor, Reza Gholami Mahmoodabadi, Verena Rauschenberger, Andreas Giessl, Alexandra Schambony, Vahid Sandoghdar
Much of the biological functions of a cell are dictated by the intricate motion of proteins within its membrane over a spatial range of nanometers to tens of micrometers and time intervals of microseconds to minutes. While this rich parameter space is not accessible to fluorescence microscopy, it can be within reach of interferometric scattering (iSCAT) particle tracking. Being sensitive even to single unlabeled proteins, however, iSCAT is easily accompanied by a large speckle-like background, which poses a substantial challenge for its application to cellular imaging. Here, we show that these difficulties can be overcome and demonstrate tracking of transmembrane epidermal growth factor receptors (EGFR) with nanometer precision in all three dimensions at up to microsecond speeds and tens of minutes duration. We provide unprecedented examples of nanoscale motion and confinement in ubiquitous processes such as diffusion in the plasma membrane, transport on filopodia, and endocytosis.
Polarization-Tailored Raman Frequency Conversion in Chiral Gas-Filled Hollow-Core Photonic Crystal Fibers
Sona Davtyan, David Novoa, Yang Chen, Michael H. Frosz, Philip St. J. Russell
Broadband-tunable sources of circularly polarized light are crucial in fields such as laser science, biomedicine, and spectroscopy. Conventional sources rely on nonlinear wavelength conversion and polarization control using standard optical components and are limited by the availability of suitably transparent crystals and glasses. Although a gas-filled hollow-core photonic crystal fiber provides pressuretunable dispersion, long well-controlled optical path lengths, and high Raman conversion efficiency, it is unable to preserve a circular polarization state, typically exhibiting weak linear birefringence. Here we report a revolutionary approach based on a helically twisted hollow-core photonic crystal fiber, which displays circular birefringence, thus robustly maintaining a circular polarization state against external perturbations. This makes it possible to generate pure circularly polarized Stokes and anti-Stokes signals by rotational Raman scattering in hydrogen. The polarization state of the frequency-shifted Raman bands can be continuously varied by tuning the gas pressure in the vicinity of the gain-suppression point. The results pave the way to a new generation of compact and efficient fiber-based sources of broadband light with a fully controllable polarization state.
Huygens' Dipole for Polarization-Controlled Nanoscale Light Routing
Sergey Nechayev, Jörg Eismann, Martin Neugebauer, Pawel Wozniak, Ankan Bag, Gerd Leuchs, Peter Banzer
Physical Review A
99(4)
041801
(2019)
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Structured illumination allows for satisfying the first Kerker condition of in-phase perpendicular electric and magnetic dipole moments in any isotropic scatterer that supports electric and magnetic dipolar resonances. The induced Huygens' dipole may be utilized for unidirectional coupling to waveguide modes that propagate transverse to the excitation beam. We study two <br> configurations of a Huygens' dipole -- longitudinal electric and transverse magnetic dipole moments or vice versa. We experimentally show that only the radially polarized emission of the first and azimuthally polarized emission of the second configuration are directional in the far-field. This polarization selectivity implies that directional excitation of either TM or TE waveguide modes is possible. Applying this concept to a single nanoantenna excited with structured light, we are able to experimentally achieve scattering directivities of around 23 dB and 18 dB in TM and TE modes, respectively. This strong directivity paves the way for tunable polarization-controlled nanoscale light routing and applications in optical metrology, <br> ocalization microscopy and on-chip optical devices.
Seeded and unseeded high-order parametric down-conversion
Cameron Okoth, Andrea Cavanna, Nicolas Joly, Maria Chekhova
Spontaneous parametric down-conversion (SPDC) has been one of the foremost tools in quantum optics for over five decades. Over that time, it has been used to demonstrate some of the curious features that arise from quantum mechanics. Despite the success of SPDC, its higher-order analogs have never been observed, even though it has been suggested that they generate far more unique and exotic states than SPDC. An example of this is the emergence of non-Gaussian states without the need for postselection. Here we calculate the expected rate of emission for nth-order SPDC with and without external stimulation (seeding). Focusing primarily on third-order parametric down-conversion, we estimate the photon detection rates in a rutile crystal for both the unseeded and seeded regimes.
Study of broadband multimode light via non-phase-matched sum frequency generation
Denis Kopylov, Kirill Spasibko, Tatiana Murzina, Maria Chekhova
New Journal of Physics
21
033024
(2019)
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We propose non-phase-matched sum frequency generation (SFG) as a method for characterizing broadband multimode light. Both the central wavelength and the bandwidth are in this case not limited by the phase matching condition. As an example, we consider bright squeezed vacuum (BSV) generated through high-gain parametric down conversion (PDC). In the spectrum of SFG from BSV, we observe the coherent peak and the incoherent background. We show that the ratio of their widths is equal to the number of frequency modes in BSV, which in the case of low-gain PDC gives the degree of frequency entanglement for photon pairs. By generating the sum frequency in the near-surface region of a nonlinear crystal, we increase the SFG efficiency and get rid of the modulation caused by chromatic dispersion, known as Maker fringes. This allows one to use non-phasematched SFG as a wavelength-independent autocorrelator. Furthermore, we demonstrate efficient non-phase-matched three- and four-frequency summation of broadband multimode light, hardly possible under phase matching. We show that the latter contains the coherent peak while the former does not.
Pulse-repetition-rate tuning of a harmonically mode-locked fiber laser using a tapered photonic crystal fiber
Dung-Han Yeh, Wenbin He, Meng Pang, Xin Jiang, Gordon K. L. Wong, Philip St J. Russell
Strong enhancement of optoacoustic interactions in the micrometer-sized core of a photonic crystal fiber (PCF) enables stable, harmonic mode locking of a soliton fiber laser<br>at GHz frequencies. Here we report that by tapering the PCF during the draw, the optoacoustic gain bandwidth can be broadened to ∼47 MHz, more than 3 times wider than in the untapered fiber. This made possible broad pulse-repetition-rate tuning over 66 MHz (from 2.042 to 2.108 GHz) of an optoacoustically mode-locked soliton fiber laser. Within this tuning range, the harmonically mode-locked pulse trains at the laser output were observed to be quite robust, with better than 40 dB supermode suppression ratio, sub-ps pulse timing jitter, and <0.2% relative intensity noise. This gigahertz-rate, near-infrared soliton fiber laser has remarkable pulse-rate tunability and low noise level, and has important potential applications in frequency metrology, high-speed optical sampling, and fiber telecommunications.
Overcoming inefficient detection in sub-shot-noise absorption measurement and imaging
Eugene Knyazev, Farid Khalili, Maria Chekhova
Optics Express
27(6)
7868-7885
(2019)
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Journal
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Photon-number squeezing and correlations enable measurement of absorption with an accuracy exceeding that of the shot-noise limit. However, sub-shot noise imaging and sensing based on these methods require high detection efficiency, which can be a serious obstacle if measurements are carried out in “difficult” spectral ranges. We show that this problem can be overcome through the phase-sensitive amplification before detection. Here we propose an experimental scheme of sub-shot-noise imaging with tolerance to detection losses.
Adaptive Compressive Tomography with No a priori Information
Daekun Ahn, Yong Siah Teo, Hyunseok Jeong, Frédéric Bouchard, Felix Hufnagel, Ebrahim Karimi, D Koutny, Jarda Rehacek, Zdenek Hradil, et al.
Physical Review Letters
122
(2019)
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Quantum state tomography is both a crucial component in the field of quantum information and computation and a formidable task that requires an incogitable number of measurement configurations as the system dimension grows. We propose and experimentally carry out an intuitive adaptive compressive tomography scheme, inspired by the traditional compressed-sensing protocol in signal recovery, that tremendously reduces the number of configurations needed to uniquely reconstruct any given quantum state without any additional a priori assumption whatsoever (such as rank information, purity, etc.) about the state, apart from its dimension.
Initialisation of single spin dressed states using shortcuts to adiabaticity
Johannes Kölbl, Arne Barfuss, Mark Kasperczyk, Lucas Thiel, Aashish Clerk, Hugo Ribeiro, Patrick Maletinsky
Physical Review Letters
122(9)
090502
(2019)
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We demonstrate the use of shortcuts to adiabaticity protocols for initialisation, readout, and coherent control of dressed states generated by closed-contour, coherent driving of a single spin. Such dressed states have recently been shown to exhibit efficient coherence protection, beyond what their two-level counterparts can offer. Our state transfer protocols yield a transfer fidelity of ~ 99.4(2) % while accelerating the transfer speed by a factor of 2.6 compared to the adiabatic approach. We show bi-directionality of the accelerated state transfer, which we employ for direct dressed state population readout after coherent manipulation in the dressed state manifold. Our results enable direct and efficient access to coherence-protected dressed states of individual spins and thereby offer attractive avenues for applications in quantum information processing or quantum sensing.
A primary radiation standard based on quantum nonlinear optics
Samuel Lemieux, Enno Giese, Robert Fickler, Maria Chekhova, Robert Boyd
The black body remains the most prominent source of light for absolute radiometry. Its main alternative, synchrotron radiation, requires costly and large facilities. Quantum optics offers a new radiometric source: parametric down-conversion (PDC), a nonlinear optical process, in which pairwise photon correlations enable absolute calibration of photodetectors. Since the emission rate crucially depends on the brightness of the electromagnetic field, quantum-mechanical fluctuations of the vacuum can be seen as a seed of spontaneous PDC, and their amplitude is a natural radiometric standard. Thus, they allow for the calibration of the spectral radiance of light sources by measuring the ratio between seeded and unseeded PDC. Here, we directly use the frequency spectrum of the electromagnetic vacuum to trigger spontaneous PDC and employ the generated light to infer the spectral response of a spectrometer over a broad spectral range. Then, we deduce the absolute quantum efficiency from the spectral shape of PDC in the high-gain regime, without relying on a seed or reference detector. Our results compare well with the ones obtained with a reference lamp, demonstrating a promising primary radiation standard.
Loop geometry is a frequent encounter in synthetic and biological polymers. Here we provide an analytical theory to characterize the shapes of polymer loops subjected to an external force field. We show how to calculate the polymer density, gyration radius and its distribution. Interestingly, the distribution of the gyration radius shows a non-monotonic behavior as a function of the external force. Furthermore, we analyzed the gyration tensor of the polymer loop characterizing its overall shape. Two parameters called asphericity and the nature of asphericity derived from the gyration tensor, along with the gyration radius, can be used to quantify the shape of polymer loops in theory and experiments.
Super- and subradiance of clock atoms in multimode optical waveguides
Laurin Ostermann, Clément Meignant, Claudiu Genes, Helmut Ritsch
The transversely confined propagating modes of an optical fiber mediate virtually infinite range energy exchanges among atoms placed within their field, which adds to the inherent free space dipole–dipole coupling. Typically, the single atom free space decay rate largely surpasses the emission rate into the guided fiber modes. However, scaling up the atom number as well as the system size amounts to entering a collective emission regime, where fiber-induced superradiant spontaneous emission dominates over free space decay. We numerically study this super- and subradiant decay of highly excited atomic states for one or several transverse fiber modes as present in hollow core fibers. As particular excitation scenarios we compare the decay of a totally inverted state to the case of π/2 pulses applied transversely or along the fiber axis as in standard Ramsey or Rabi interferometry. While a mean field approach fails to correctly describe the initiation of superradiance, a second-order approximation accounting for pairwise atom–atom quantum correlations generally proves sufficient to reliably describe superradiance of ensembles from two to a few hundred particles. In contrast, a full account of subradiance requires the inclusion of all higher order quantum correlations. Considering multiple guided modes introduces a natural effective cut-off for the interaction range emerging from the dephasing of different fiber contributions.
Orbital-to-Spin Angular Momentum Conversion Employing Local Helicity
Sergey Nechayev, Jörg Eismann, Gerd Leuchs, Peter Banzer
Physical Review B
99(7)
075155
(2019)
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Spin-orbit interactions in optics traditionally describe an influence of the polarization degree of freedom of light on its spatial properties. The most prominent example is the generation of a spin-dependent optical vortex upon focusing or scattering of a circularly polarized plane-wave by a nanoparticle, converting spin to orbital angular momentum of light. Here, we present a mechanism of conversion of orbital-to-spin angular momentum of light upon scattering of a linearly polarized vortex beam by a spherical silicon nanoparticle. We show that focused linearly polarized Laguerre-Gaussian beams of first order (ℓ=±1) exhibit an ℓ-dependent spatial distribution of helicity density in the focal volume. By using a dipolar scatterer the helicity density can be manipulated locally, while influencing globally the spin and orbital angular momentum of the beam. Specifically, the scattered light can be purely circularly polarized with the handedness depending on the orbital angular momentum of the incident beam. We corroborate our findings with theoretical calculations and an experimental demonstration. Our work sheds new light on the global and local properties of helicity conservation laws in electromagnetism.
Turning a molecule into a coherent two-level quantum system
Daqing Wang, Hrishikesh Kelkar, Diego-Martin Cano, Dominik Rattenbacher, Alexey Shkarin, Tobias Utikal, Stephan Götzinger, Vahid Sandoghdar
The use of molecules in quantum optical applications has been hampered by incoherent internal vibrations and other phononic interactions with their environment. Here we show that an organic molecule placed into an optical microcavity behaves as a coherent two-level quantum system. This allows the observation of 99% extinction of a laser beam by a single molecule, saturation with less than 0.5 photons and non-classical generation of few-photons super-bunched light. Furthermore, we demonstrate efficient interaction of the molecule–microcavity system with single photons generated by a second molecule in a distant laboratory. Our achievements represent an important step towards linear and nonlinear quantum photonic circuits based on organic platforms.
Classically Entangled Light
Andrew Forbes, Andrea Aiello, Bienvenu Ndagano
Progress in Optics
64
99-153
(2019)
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Book Chapter
The concept of entanglement is so synonymous with quantum mechanics that the prefix “quantum” is often deemed unnecessary; there is after all only quantum entanglement. But the hallmark of entangled quantum states is nonseparability, a property that is not unique to the quantum world. On the contrary, nonseparability appears in many physical systems, and pertinently, in classical vector states of light: classical entanglement? Here we outline the concept of classical entanglement, highlight where it may be found, how to control and exploit it, and discuss the similarities and differences between quantum and classical entangled systems. Intriguingly, we show that quantum tools may be applied to classical systems, and likewise that classical light may be used in quantum processes. While we mostly use vectorial structured light throughout the text as our example of choice, we make it clear that the concepts outlined here may be extended beyond this with little effort, which we showcase with a few selected case studies.
Direct characterization of tuneable few-femtosecond dispersive-wave pulses in the deep UV
Christian Brahms, Dane R. Austin, Francesco Tani, Allan S. Johnson, Douglas Garratt, John. C. Travers, John W. G. Tisch, Philip Russell, Jon P. Marangos
Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherentand broadband radiation, but so far the generation of fewfemtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterize tuneable 3 fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.
Identifying the mechanism for superdiffusivity in mouse fibroblast motility
Giuseppe Passucci, Megan E. Brasch, James H. Henderson, Vasily Zaburdaev, M. Lisa Manning
We seek to characterize the motility of mouse fibroblasts on 2D substrates. Utilizing automated tracking techniques, we find that cell trajectories are super-diffusive, where displacements scale faster than t(1/2) in all directions. Two mechanisms have been proposed to explain such statistics in other cell types: run and tumble behavior with Levy-distributed run times, and ensembles of cells with heterogeneous speed and rotational noise. We develop an automated toolkit that directly compares cell trajectories to the predictions of each model and demonstrate that ensemble-averaged quantities such as the mean-squared displacements and velocity autocorrelation functions are equally well-fit by either model. However, neither model correctly captures the short-timescale behavior quantified by the displacement probability distribution or the turning angle distribution. We develop a hybrid model that includes both run and tumble behavior and heterogeneous noise during the runs, which correctly matches the short-timescale behaviors and indicates that the run times are not Levy distributed. The analysis tools developed here should be broadly useful for distinguishing between mechanisms for superdiffusivity in other cells types and environments.
The Wigner flow on the sphere
P. Yang, I. F. Valtierra, A. B. Klimov, S. -T. Wu, R. -K. Lee, Luis Sanchez-Soto, Gerd Leuchs
Physica Scripta
94(4)
044001
(2019)
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We derive a continuity equation for the evolution of the SU(2) Wigner function under nonlinear Kerr evolution. We give explicit expressions for the resulting quantum Wigner current, and discuss the appearance of the classical limit. We show that the global structure of the quantum current significantly differs from the classical one, which is clearly reflected in the form of the corresponding stagnation lines.
Interference effects in hybrid cavity optomechanics
Ondrej Černotík, Claudiu Genes, Aurelien Dantan
Quantum Science and Technology
4(2)
024002
(2019)
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Journal
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Radiation pressure forces in cavity optomechanics allow for efficient cooling of vibrational modes of macroscopic mechanical resonators, the manipulation of their quantum states, as well as generation of optomechanical entanglement. The standard mechanism relies on the cavity photons directly modifying the state of the mechanical resonator. Hybrid cavity optomechanics provides an alternative approach by coupling mechanical objects to quantum emitters, either directly or indirectly via the common interaction with a cavity field mode. While many approaches exist, they typically share a simple effective description in terms of a single force acting on the mechanical resonator. More generally, one can study the interplay between various forces acting on the mechanical resonator in such hybrid mechanical devices. This interplay can lead to interference effects that may, for instance, improve cooling of the mechanical motion or lead to generation of entanglement between various parts of the hybrid device. Here, we provide such an example of a hybrid optomechanical system where an ensemble of quantum emitters is embedded into the mechanical resonator formed by a vibrating membrane. The interference between the radiation pressure force and the mechanically modulated Tavis--Cummings interaction leads to enhanced cooling dynamics in regimes in which neither force is efficient by itself. Our results pave the way towards engineering novel optomechanical interactions in hybrid optomechanical systems.
Weak measurement enhanced spin Hall effect of light for particle displacement sensing
Martin Neugebauer, Sergey Nechayev, Martin Vorndran, Gerd Leuchs, Peter Banzer
A spherical nanoparticle can scatter tightly focused optical beams in a spin-segmented manner, meaning that the far field of the scattered light exhibits laterally separated left- and right-handed circularly polarized components. This effect, commonly referred to as giant spin Hall effect of light, strongly depends on the position of the scatterer in the focal volume. Here, a scheme that utilizes an optical weak measurement in a cylindrical polarization basis is put forward to drastically enhance the spin-segmentation and, therefore, the sensitivity to small displacements of a scatterer. In particular, we experimentally achieve a change of the spin-splitting signal of 5% per nanometer displacement.
Quantum Magnetism, Spin Waves, and Optical Cavities
This primer thoroughly covers the fundamentals needed to understand the interaction of light with magnetically ordered matter and it focuses on "cavity optomagnonics" which is a topic undergoing intense study in current research.<br>The book is unique in combining elements of electromagnetism, quantum magnetism, and quantum optics and it is intended for advanced undergraduate or graduate students.
High throughput magnetic tweezers to characterize inhibitors of RNA virus replication
Journal of Physics: Conference Series
1275
012026
(2019)
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Journal
We describe in this paper the effects of Lorentz boost on the quantum entanglement encoded in two-particle Dirac bispinor Bell-like states. Each particle composing the system described in this formalism has three degrees of freedom: spin, chirality, and momentum, and the joint state can be interpreted as a 6 qubit state. Given the transformation law of bispinor under boosts, we compute the change of the Meyer-Wallach global measure of quantum entanglement due to the frame transformation and study its equivalence to the results obtained for the relativistic spin 1/2 Bell-like states, constructed in the framework of the irreducible representations of the Lorentz group. We verify that the monotonic increase of the global entanglement under boosts for ultra-relativistic states is solely due to an increasing of the entanglement associated with the spins subsystems. For such ultra-relativistic states, the entanglement related to the chirality degrees of freedom is invariant, and the variation of the global entanglement of bispinor states is the same as the one calculated for relativistic spin 1/2 states. We also show that the particle-particle entanglement is invariant under boosts for any Bell-like state.
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Max-Planck-Zentren und -Schulen
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