Publications of the Max Planck Institute for the Science of Light

The oscillating electric field emitted by excitons in layered antiferromagnets reveals how quasiparticles synchronize into collective coherence and shows that a complex multi-peak spectrum can arise from a single excitonic resonance dynamically modulated by spin and lattice excitations.

The glycocalyx is a complex layer of glycosylated molecules that surrounds all cells in the human body. It is involved in regulating critical cellular processes, including immune response modulation, cell adhesion and host–pathogen interactions. Despite these insights, the functional relationship between the glycocalyx architecture and cellular state has remained elusive, largely due to the structural diversity of glycocalyx constituents and their nanoscale organization. Here we show that DNA-tagged lectin labelling and metabolic oligosaccharide engineering enable multiplexed super-resolution microscopy of the glycocalyx constituents, yielding an atlas of glycocalyx architecture with nanometre resolution. Quantitative analysis of the obtained nanoscale map of glycocalyx constituents facilitates the extraction of characteristic spatial relationships that accurately report on the cellular state. We demonstrate the capacity of our approach, which we term glycan atlassing, across cell and tissue types, ranging from cultured cell lines to primary immune cells, neurons and primary patient tissue. Glycan atlassing establishes a transformative strategy for investigating glycocalyx remodelling in development and disease, potentially enabling the development of glycocalyx-centred targets in diagnosis and therapy.

We show topological configurations of the complex-valued spectra in gapped non-Hermitian systems. These arise when the distinctive EPs in the energy Riemann sheets of such models are annihilated after threading them across the boundary of the Brillouin zone. This results in a non-trivially closed branch cut that is protected by an energy gap in the spectrum. Their presence or absence establishes topologically distinct configurations for fully non-degenerate systems and tuning between them requires a closing of the gap, forming exceptional point degeneracies. We provide an outlook toward experimental realizations in metasurfaces and single-photon interferometry.

Multimode squeezed light is a key resource for high-dimensional quantum technologies, enhancing metrological sensitivity, boosting communication security, and enabling parallel processing in computation. Its practical potential, however, remains constrained by the inherent single-mode operation of homodyne detection, necessitating post-processing for multimode characterization. Here, we overcome this long-standing challenge by employing multimode optical parametric amplification, enabling loss-tolerant direct detection of squeezing in each mode, which in turn permits mode sorting after amplification. As a result, we demonstrate, for the first time to the best of our knowledge, the real-time monitoring of multimode squeezing. With a spatial light modulator sorting the modes, we simultaneously measure squeezing in nine spatial modes co-propagating within one beam. Although mode sorting and filtering reduce the detection efficiency to less than 0.3%, we observe high-purity squeezing of up to − 7.9 ± 0.6 dB – to the best of our knowledge, the highest squeezing recorded for pulsed light. Furthermore, we demonstrate real-time, loss-tolerant characterization of continuous-variable entanglement and extend it to the detection of cluster states. Similar methods can be applied in the frequency domain, facilitating a crucial capability for scalable quantum technologies.

The development of single-photon sources has been nothing but rapid in recent years, with quantum emitter-based systems showing especially impressive progress. In this paper, we give an overview of the developments in single-photon sources based on single molecules. We will introduce polycyclic hydrocarbons as the most commonly used emitter systems for the realization of an organic solid-state single-photon source. At cryogenic temperatures, this special class of fluorescent molecules demonstrates remarkable optical properties such as negligible dephasing, indefinite photostability, and high photon rates, which make them attractive as fundamental building blocks in emerging quantum technologies. To better understand the general properties and limitations of these molecules, we discuss sample preparation and relevant emitter parameters such as absorption and emission spectra, lifetime, and dephasing. We will also give an overview of light extraction strategies as a crucial part of a single-photon source. Finally, we conclude with a look into the future, displaying current challenges and possible solutions.

The ranges of existence and stability of dark cavity-soliton stationary states in a Fabry-Pérot resonator with a Kerr nonlinear medium, vectorial polarization components, and normal dispersion are determined. The Fabry-Pérot configuration introduces nonlocal coupling that shifts the cavity detuning by the round-trip average power of the intracavity field. When compared with ring resonators, nonlocal coupling leads to strongly detuned dark cavity solitons that exist over a wide range of detunings. We study symmetry breaking between fields of opposite circular polarization characterized by a codimension-2 bifurcation point unique to the regime of normal group velocity dispersion. We show the spontaneous formation of regular dark soliton crystals separated by Turing patterns of alternating polarization via ‘‘self-crystallization’’ due to long-range interactions. Frequency combs of dark soliton crystals of two orthogonal polarizations in Fabry-Pérot resonators display three separate components corresponding to the cavity repetition rate, the wavelength of the periodic pattern, and the soliton lattice spacing. The system also displays the formation of stationary and dynamical vectorial dark-bright solitons. These solutions are different from previous realizations with bichromatic driving in ring resonators, are composed of locked switching fronts, and can undergo Hopf bifurcations when scanning the detuning. Interacting oscillating dark-bright solitons display antiphase dynamics that changes first into quasiperiodic oscillations and then into in-phase dynamics when increasing the cavity length.

Stimulated Raman scattering (SRS) microscopy has emerged as a powerful technique for probing the spatiotemporal dynamics of molecular bonds with exceptional sensitivity, resolution, and speed. However, classically, its performance remains fundamentally constrained by optical shot noise, which imposes a strict limit on detection sensitivity and speed. Here, we demonstrate a quantum-enhanced SRS microscopy platform that circumvents this barrier by harnessing amplitude-squeezed light. Specifically, we generate a Stokes beam with 5.2 dB of amplitude squeezing using traveling-wave optical parametric amplification in second-order nonlinear waveguides, and combine it with a tunable coherent pump to access vibrational modes spanning from 1000 to 3100 cm−1. Applied to quantum imaging of metabolites in biological tissue (pork muscle), our quantum-enhanced Raman microscope achieves an average noise suppression of 3.6 dB and a 51% enhancement in signal-to-noise ratio (SNR)— to the best of our knowledge, the largest improvement reported to date in quantum-enhanced SRS microscopy of biological samples.

The integration of optical imaging and machine learning on microfluidic platforms makes it possible to achieve high-content minimally invasive characterization of a population of samples on a single chip As the analysis of this high-content information is typically conducted in the electronic domain optoelectronic conversion speeds and the bandwidth available for data processing put a limitation on the throughput of these methods In this work we present an analysis system based on diffractive neural networks with the potential for integration in microfluidic systems for high-content classification of objects with high sampling rates We show that such a system can distinguish objects by size through passive optical inference with a numerical test accuracy of 98.2 and an experimental test accuracy of 83.4 in an environment compatible with a microfluidic chamber This development paves the way for novel approaches in high-speed phenotyping of large cell populations based on all-optical or hybrid optoelectronic neuromorphic information processing.

The mechanical properties of cells are dynamic, allowing them to adjust to different needs in different biological contexts. In recent years, advanced biophysical techniques have enabled the rapid, high-throughput assessment of single-cell mechanics, providing new insights into the regulation of the mechanical cell phenotype. However, the molecular mechanisms by which cells maintain and regulate their mechanical properties remain poorly understood. Here, we present a genome-scale RNA interference (RNAi) screen investigating the roles of kinase and phosphatase genes in regulating single-cell mechanics using Real-Time Fluorescence and Deformability Cytometry (RT-FDC). Our screen identified 82 known and novel mechanical regulators across diverse cellular functions from 214 targeted genes, leveraging RT-FDC’s unique capabilities for comprehensive, high-throughput mechanical phenotyping with single-cell and cell cycle resolution. These findings refine our understanding of how signaling pathways coordinate structural determinants of cell mechanical phenotypes and provide a starting point for uncovering new molecular targets involved in biomechanical regulation across diverse biological systems.

Deformability cytometry (DC) is a powerful biophysical technique that enables cost-effective, high-throughput characterization of disease-associated changes in blood cell mechanics. Mechanical profiling of living white blood cells (WBCs) is particularly valuable due to their critical role in the immune response. However, reliably identifying and classifying WBC subtypes in a label-free manner remains a significant challenge. Until now, the analysis pipeline has relied on manual gating by trained experts, limiting scalability and reproducibility. In this study, we present a fully automated and generalizable framework for WBC classification in shear flow DC experiments, based on box filters and unsupervised clustering of cell populations. Both box filters and unsupervised clustering rely on cell shape features derived from high-accuracy segmentation and on cell texture features derived from bright-field images. This unsupervised approach not only improves reproducibility and reduces processing time but also overcomes key limitations of supervised models that require extensive training data and often suffer from reduced performance under varying imaging conditions. We validated our method by comparing cell features obtained through manual gating and automated classification across six experimental sets. These sets incorporated variations in blood donors, anticoagulants (EDTA and citrate), blood collection sources (capillary and venous), and device brightness settings. Each set included five repeated measurements. The results consistently confirmed the reliability and robustness of the method across all tested conditions and WBC types. Importantly, this automated pipeline enables the inclusion of WBCs with membrane protrusions—typically excluded from standard analyses—allowing for morphological characterization of potentially activated cells. Moreover, by using shape features derived from the original contour rather than the convex hull, we improve morphological accuracy and reduce measurement variability. This approach thus enhances the accuracy, consistency, and scalability of WBC mechanophenotyping and enables high-throughput analysis across large cohorts.

Scalable, high-speed, small-footprint photonic switching platforms are essential for advancing optical communication. An effective optical switch must operate at high duty cycles with fast recovery times, while maintaining substantial modulation depth and full reversibility. Colloidal nanocrystals, such as indium tin oxide (ITO), offer a scalable platform to meet these requirements. In this work, the transmission of ITO nanocrystals near their epsilon-near-zero wavelength is modulated by two-cycle optical pulses at a repetition rate of one megahertz. The modulator exhibits a broad bandwidth spanning from 2 to 2.5 µm. Sensitive fieldoscopy measurements resolve the transient electric-field response of the ITO for the first time, showing that the modulation remains reversible for excitation fluences up to 1.2 mJ cm−2 with a modulation depth of 10%, and becomes fully irreversible beyond 3.3 mJ cm−2, while reaching modulation depth of up to 20%. Field sampling further indicates that at higher excitation fluences, the relative contribution from the first cycle of the optical pulses is reduced. These findings are crucial for the development of all-optical switching, telecommunications, and sensing technologies capable of operating at terahertz switching frequencies.

INTRODUCTION: Pathogenic variants in myosin heavy chain 9 (MYH9) encoding the heavy chain of nonmuscle myosin IIA (NMMIIA) cause autosomal-dominant MYH9-related disease that may include proteinuric kidney disease macrothrombocytopenia cataract sensorineural deafness and elevated liver enzymes. METHODS: Whole exome sequencing and segregation analysis were performed in a patient with end-stage renal disease Histology of kidney and liver biopsies was assessed and blood smears were examined for the presence of Döhle-like bodies Deformability cytometry and monocyte migration assays were performed Immortalized podocytes and primary skin fibroblasts of 1 patient were transfected with plasmids containing MYH9 wild type (WT) or the p.(Arg424Gly) variant Biochemical studies using recombinantly produced proteins were conducted to assess the variant’s impact on adenosine triphosphate (ATP) turnover and motor function. RESULTS: We identified the likely pathogenic heterozygous MYH9 variant c.1270C>G p.(Arg424Gly) in all affected members of a nonconsanguineous family Typical microscopic findings such as Döhle-like bodies or NMMIIA conglomerates were absent Nonetheless all patients presented with proteinuric kidney disease elevated liver enzymes and intermittent thrombocytopenia The altered protein showed increased ATP turnover in the presence of actin and enhanced motor activity under both unloaded and loaded conditions. CONCLUSION: We identified a novel fully segregating MYH9 variant causing MYH9-related disease Based on biochemical findings we report the first gain-of-function variant of MYH9 We propose that the enhanced intrinsic motor activity of the p.(Arg424Gly) variant is a key contributor to the disease mechanism Incorporation of the p.(Arg424Gly) variant into nonmuscle myosin IIA filaments and higher-order actomyosin assemblies may in principle affect actomyosin dynamics.

The use of hollow-core photonic crystal fibers in operando spectrometry of chemical reactions is a relatively unexplored technology. It can be used in different ways and offers a variety of advantages compared with conventional operando spectrometry, such as a significantly increased path length with a simultaneously reduced volume. We apply fiber absorption spectroscopy here to the synthesis of gold nanoparticles. We measured the rate of formation of gold nanoparticles at different initial concentrations. We show that much higher resolution is possible with this technique in comparison with a conventional measurement technique using cuvettes.

Flat-optics platforms offer new opportunities for the generation of entangled photons by relaxing traditional phase-matching constraints, enabling the use of a broader range of nonlinear materials. Among these, gallium arsenide and aluminum gallium arsenide stand out for their exceptionally high second-order nonlinearities, but their conventional orientation (001) has limited their applicability for photon-pair generation. By transitioning to crystals with (111) surface orientation, we overcome these limitations. We demonstrate a flat-optics-based telecom-range SPDC source using Al0.30Ga0.70As that achieves a high photon-pair generation rate per pump power and bandwidth of up to 0.24 Hz/mW/nm. The choice of 30% aluminum concentration allowed us to reduce pump absorption and photoluminescence background for photon-pair generation at telecom wavelengths by at least an order of magnitude compared to that of GaAs. The specific layer orientation facilitates the generation of orthogonally polarized entangled photons, a prerequisite for polarization-entangled states. Rather than directly probing entanglement, we observe the effect of hidden polarization. Our results highlight AlGaAs (111) as a promising platform for scalable quantum photonic sources and shed light on nonclassical polarization effects accessible through flat-optics engineering.

Shaping polyacrylamide (PAAm) hydrogels via droplet microfluidics enables production of microgels that mimic cellular physical properties, advancing mechanobiology research. Controlling microgel size and elasticity is essential but challenging, as multiple factors influence polymerization and network formation. Although chemical reactions in microdroplets are generally faster and more uniform than in bulk, these microreactors are highly sensitive: small changes in chemical or physical conditions can cause significant variations in microgel properties. Our study identifies flow conditions as a crucial factor affecting both microgel elasticity and size by modulating interfacial transport during gelation. Using a flow-focusing microfluidic chip, we generated pre-gel droplets with the same composition in an oil phase, systematically varying the PAAm-to-oil flow rate ratio while maintaining a constant total flow rate. This method produced droplets with minimal size variation (<1 µm), but beads exhibited distinct Young’s moduli despite identical monomer concentrations. Further analysis showed that catalyst transport across the oil–water interface strongly impacts polymerization efficiency and network structure. These findings demonstrate that while droplet polymerization offers advantages, reproducible microgel properties demand precise flow control. This work emphasizes the critical role of microfluidic parameter tuning in advancing PAAm microgel applications in biophysics.

Broadband frequency combs with mode spacings of 1 GHz provide a valuable resource for optical frequency metrology and astrophotonics. Significant average powers are often needed to reach the pulse energies required for supercontinuum generation at 1 GHz repetition rates, putting this beyond the reach of most simple ultrafast lasers. Here, by using dispersion-engineered Si₃N₄ waveguides, we report octave-spanning comb generation from 539 to 1078 nm (−20 dB bandwidth) pumped with a three-element 1 GHz Ti:sapphire laser powered by a single laser diode. Laser repetition-rate stability of 790 mHz is achieved over a 1-hour duration, and carrier-envelope-offset control and stabilization to a single-frequency cw laser is presented. The system offers a simple route to a coherent, broadband supercontinuum spanning the visible to the near-infrared, with potential as an enabling technology for optical frequency metrology, quantum timekeeping, and astrophysical spectrograph calibration.

The ongoing evolution of hollow-core fibers continues to inspire the development of optofluidic platforms with enhanced sensitivity and minimal sample requirements. Here, we utilize the intrinsic advantages of anti-resonant reflection hollow-core fibers—such as low optical loss and broadband transmission—to realize a twisted single-ring hollow-core fiber (SR-HCF) tailored for polarization-sensitive chiral detection. We optimize the fiber geometry to ensure single-mode operation by strongly attenuating higher-order modes (>50 dB/m) while maintaining low loss for the fundamental mode (<0.1 dB/m) and reducing the sample volume to only ~660 nanoliters per 34 cm fiber length. By applying a constant twist along the fiber length, we minimize birefringence and ensure stable transmission of linear polarization states with polarization extinction ratios (PER) surpassing 38 dB. After injecting an aqueous solution of an optically active molecule, we measure its optical rotation (OR) at different wavelengths with millidegree-level sensitivity and remarkable robustness against misalignment. Measurements with different enantiomeric excess concentrations are in good agreement with independent liquid chromatography characterization.

Red blood cell-derived extracellular vesicles (RBC-EVs) are emerging as promising biomaterials for next-generation drug delivery, owing to their intrinsic biocompatibility, immune evasion properties, and minimal oncogenic risk. However, their broader application is currently limited by unresolved challenges related to heterogeneity, reproducibility, and long-term storage stability. By combining discontinuous sucrose density gradient separation with high-resolution interferometric nanoparticle tracking analysis, we identified a sharp bimodal size distribution of the vesicles in freshly prepared samples. We then tracked how long-term storage at −80 °C drove its conversion into a monomodal distribution. To reproduce these conditions in a shorter time frame, we developed an “accelerated-ageing” protocol based on freeze–thaw cycles that generates RBC-EV samples with homogeneous density, size distribution, and biological activity, effectively replicating the properties of preparations stored for six months at −80 °C. This new vesicle population results stable and retains membrane integrity and cellular internalization capacity, as confirmed by surface-associated enzymatic activity assays and uptake tests in cancer cell lines. These results suggest that freezing-induced “accelerated ageing” represents an effective method for the optimization and standardization of RBC-EVs as building blocks for biomaterial and bioengineering applications.

We report a fiber-based source of femtosecond radiation that is spectrally tunable in the short-wavelength infrared region, delivering average powers at the multi-watt level. The system utilizes self-soliton frequency shifting in a hydrogen-filled hollow-core fiber, producing pulse trains at 1.1 MHz with integrated relative intensity noise below 0.3% and a polarization extinction ratio of 30 dB. This source constitutes an efficient and valid fiber-based alternative to optical parametric amplifiers for a variety of applications, including THz generation, multiphoton imaging, and high-harmonic generation.

Thermal phonons are a major source of decoherence in quantum mechanical systems. Operating in the quantum ground state is therefore often an experimental prerequisite. In addition to passive cooling in a cryogenic environment, active laser cooling enables the reduction of phonons at specific acoustic frequencies. Brillouin cooling has been used to show efficient reduction of the thermal phonon population in waveguides at GHz frequencies down to 74 K. In this Letter, we demonstrate the cooling of a 7.608 GHz acoustic mode by combining Brillouin active cooling with precooling from 77 K using liquid nitrogen. We show a 69% reduction in the phonon population, resulting in a final temperature of 24.3 +/- 1.9 K, 50 K lower than previously reported.