Intensity correlations in the Wigner representation
Mojdeh S. Najafabadi,
Luis Sanchez-Soto,
Kun Huang,
Julien Laurat,
Hanna Le Jeannic,
Gerd Leuchs
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
382
20230337
(2024)
| Journal
| PDF
We derive a compact expression for the second-order correlation function g(2)(0) of a quantum state in terms of its Wigner function, thereby establishing a direct link between g(2)(0) and the state’s shape in phase space. We conduct an experiment that simultaneously measures g(2)(0) through direct photocounting and reconstructs the Wigner function via homodyne tomography. The results confirm our theoretical predictions.
An operational distinction between quantum entanglement and classical non-separability
Natalia Korolkova,
Luis Sanchez-Soto,
Gerd Leuchs
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
382
20230342
(2024)
| Journal
| PDF
Quantum entanglement describes superposition states in multi-dimensional systems—at least two partite—which cannot be factorized and are thus non-separable. Non-separable states also exist in classical theories involving vector spaces. In both cases, it is possible to violate a Bell-like inequality. This has led to controversial discussions, which we resolve by identifying an operational distinction between the classical and quantum cases.
Robust quantum metrology with random Majorana constellations
Aaron Goldberg,
Jose Luis Romero Hervas,
Angel S Sanz,
Andrei B Klimov,
Jaroslav Rehacek,
Zdenek Hradil,
Matias Eriksson,
Robert Fickler,
Gerd Leuchs, et al.
Quantum Science and Technology
10
015053
(2024)
| Journal
| PDF
Even the most classical states are still governed by quantum theory. A number of physical systems can be described by their Majorana constellations of points on the surface of a sphere, where concentrated constellations and highly symmetric distributions correspond to the least and most quantum states, respectively. If these points are chosen randomly, how quantum will the resultant state be, on average? We explore this simple conceptual question in detail, investigating the quantum properties of the resulting random states. We find these states to be far from the norm, even in the large-number-of-particles limit, where classical intuition often replaces quantum properties, making random Majorana constellations peculiar and intriguing. Moreover, we study their usefulness in the context of rotation sensing and find numerical evidence of their robustness against dephasing and particle loss. We realize these states experimentally using light's orbital angular momentum degree of freedom and implement arbitrary unitaries with a multiplane light conversion setup to demonstrate the rotation sensing. Our findings open up new possibilities for quantum-enhanced metrology.
Ad-hoc hybrid-heterogeneous metropolitan-range quantum key distribution
network
Matthias Goy,
Jan Krause,
Oemer Bayraktar,
Philippe Ancsin,
Florian David,
Thomas Dirmeier,
Nico Doell,
Jansen Dwan,
Friederike Fohlmeister, et al.
This paper presents the development and implementation of a versatile ad-hoc metropolitan-range Quantum Key Distribution (QKD) network. The approach presented integrates various types of physical channels and QKD protocols, and a mix of trusted and untrusted nodes. Unlike conventional QKD networks that predominantly depend on either fiber-based or free-space optical (FSO) links, the testbed presented amalgamates FSO and fiber-based links, thereby overcoming some inherent limitations. Various network deployment strategies have been considered, including permanent infrastructure and provisional ad-hoc links to eradicate coverage gaps. Furthermore, the ability to rapidly establish a network using portable FSO terminals and to investigate diverse link topologies is demonstrated. The study also showcases the successful establishment of a quantum-secured link to a cloud server.
Polarization squeezing in chalcogenide fibers
Alexey V. Andrianov,
Alexey N. Romanov,
Arseny A. Sorokin,
Elena A. Anashkina,
Nikolay Kalinin,
Thomas Dirmeier,
Luis Sanchez-Soto,
Gerd Leuchs
We experimentally demonstrate the generation of polarization-squeezed light in a short piece of solid-core chalcogenide (ChG) (As2S3) fiber via the Kerr effect for femtosecond pulses at 1.56 μm. Directly measured squeezing of −2.8 dB is obtained in a setup without active stabilization.<br>Numerical simulations are in good agreement with the experimental results and indicate that the measured squeezing in our setup is mainly limited by the losses in the detection system rather than by the fiber properties.
Composable free-space continuous-variable quantum key distribution using discrete modulation
Kevin Jaksch,
Thomas Dirmeier,
Yannick Weiser,
Stefan Richter,
Oemer Bayraktar,
Bastian Hacker,
Conrad Rösler,
Imran Khan,
Stefan Petscharning, et al.
Continuous-variable (CV) quantum key distribution (QKD) allows for quantum secure communication with the benefit of being close to existing classical coherent communication. In recent years, CV QKD protocols using a discrete number of displaced coherent states have been studied intensively, as the modulation can be directly implemented with real devices with a finite digital resolution. However, the experimental demonstrations until now only calculated key rates in the asymptotic regime. To be used in cryptographic applications, a QKD system has to generate keys with composable security in the finite-size regime. In this paper, we present a CV QKD system using discrete modulation that is especially designed for urban atmospheric channels. For this, we use polarization encoding to cope with the turbulent but non-birefringent atmosphere. This will allow to expand CV QKD networks beyond the existing fiber backbone. In a first laboratory demonstration, we implemented a novel type of security proof allowing to calculate composable finite-size key rates against i.i.d. collective attacks without any Gaussian assumptions. We applied the full QKD protocol including a QRNG, error correction and privacy amplification to extract secret keys. In particular, we studied the impact of frame errors on the actual key generation.
Polarization-entangled photons from a whispering gallery resonator
Sheng-Hsuan Huang,
Thomas Dirmeier,
Golnoush Shafiee,
Kaisa Laiho,
Dmitry Strekalov,
Gerd Leuchs,
Christoph Marquardt
npj Quantum Information
10
85
(2024)
| Journal
| PDF
Crystalline whispering gallery mode resonators (WGMRs) have been shown to facilitate versatile sources of quantum states that can efficiently interact with atomic systems. These features make WGMRs an efficient platform for quantum information processing. Here, we experimentally show that it is possible to generate polarization entanglement from WGMRs by using an interferometric scheme. Our scheme gives us the flexibility to control the phase of the generated entangled state by changing the relative phase of the interferometer. The S value of Clauser–Horne–Shimony–Holt’s inequality in the system is 2.45 ± 0.07, which violates the inequality by more than six standard deviations.
Gulia Bikbaeva,
Anna Pilip,
Anastasiya Egorova,
Vasiliy Medvedev,
Daria Mamonova,
Dmitrii Pankin,
Alexey Kalinichev,
Natalya Mayachkina,
Lyudmila Bakina, et al.
Nanoscale Advances
6
4417-4425
(2024)
| Journal
| PDF
The combination of photoswitchability and bioactivity in one compound provides interesting opportunities for photopharmacology. Here, we report a hybrid compound that in addition allows for its visual localization. It is the first demonstration of its kind and it even shows high photoswitchability. The multifunctional nanomaterial hybrid, which we present, is composed of luminescent LaVO4:Eu3+ nanoparticles and vinyl phosphonate, the latter of which inhibits butyrylcholinesterase (BChE). This inhibition increases 7 times when irradiated with a 266 nm laser. We found that it is increased even further when vinyl phosphonate molecules are conjugated with LaVO4:Eu3+ nanoparticles, leading in total to a 20-fold increase in BChE inhibition upon laser irradiation. The specific luminescence spectrum of LaVO4:Eu3+ allows its spatial localization in various biological samples (chicken breast, Daphnia and Paramecium). Furthermore, laser irradiation of the LaVO4:Eu3+@vinyl phosphonate hybrid leads to a drop in luminescence intensity and in lifetime of the Eu3+ ion that can implicitly indicate photoswitching of vinyl phosphonate in the bioactive state. Thus, combining enhanced photoswitchability, bioactivity and luminescence induced localizability in a unique way, hybrid LaVO4:Eu3+@vinyl phosphonate can be considered as a promising tool for photopharmacology.
Covariant operator bases for continuous variables
Aaron Z. Goldberg,
Andrei B. Klimov,
Gerd Leuchs,
Luis Sanchez-Soto
Coherent-state representations are a standard tool to deal with continuous-variable systems, as they allow one to efficiently visualize quantum states in phase space. Here, we work out an alternative basis consisting of monomials on the basic observables, with the crucial property of behaving well under symplectic transformations. This basis is the analogue of the irreducible tensors widely used in the context of SU(2) symmetry. Given the density matrix of a state, the expansion coefficients in that basis constitute the multipoles, which describe the state in a canonically covariant form that is both concise and explicit. We use these quantities to assess properties such as quantumness or Gaussianity and to furnish direct connections between tomographic measurements and quasiprobability distribution reconstructions.
Quantum squeezing via self-induced transparency in a photonic crystal fiber
Mojdeh S. Najafabadi,
Luis Sanchez-Soto,
J. F. Corney,
Nikolay Kalinin,
A. A. Sorokin,
Gerd Leuchs
Physical Review Research
6
023142
(2024)
| Journal
| PDF
We study the quantum squeezing produced in self-induced transparency in a photonic crystal fiber by performing a fully quantum simulation based on the positive P representation. The amplitude squeezing depends on the area of the initial pulse: When the area is 2 pi, there is no energy absorption and no amplitude squeezing. However, when the area is between 2 pi and 3 pi, one observes amplitude-dependent energy absorption and a significant amount of squeezing. We also investigate the effect of damping, detuning, and temperature: The results indicate that a heightened atom-pulse coupling, caused by an increase in the spontaneous emission ratio, reduces the amplitude squeezing.
Multipoles from Majorana constellations
J. L. Romero,
A. B. Klimov,
A. Z. Goldberg,
Gerd Leuchs,
Luis Sanchez-Soto
Physical Review A
109
012214
(2024)
| Journal
| PDF
Majorana stars, the 2S spin coherent states that are orthogonal to a spin-S state, offer an elegant method to visualize quantum states, disclosing their intrinsic symmetries. These states are naturally described by the corresponding multipoles. These quantities can be experimentally determined and allow for an SU(2)-invariant analysis. We investigate the relationship between Majorana constellations and state multipoles, thus providing insights into the underlying symmetries of the system. We illustrate our approach with some relevant and informative examples.
MPL Research Centers and Schools
Data Collection
This website uses cookies to ensure you get the best experience on our website.
