@article{63656,
  author       = {{Ares, Laura and Pinske, Julien and Hinrichs, Benjamin and Kolb, Martin and Sperling, Jan}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{1}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Restricted Monte Carlo wave-function method and Lindblad equation for identifying entangling open-quantum-system dynamics}}},
  doi          = {{10.1103/hcj7-8zlg}},
  volume       = {{113}},
  year         = {{2026}},
}

@article{63657,
  author       = {{Pinske, Julien and Ares, Laura and Hinrichs, Benjamin and Kolb, Martin and Sperling, Jan}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{1}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Separability Lindblad equation for dynamical open-system entanglement}}},
  doi          = {{10.1103/kd3b-bfxq}},
  volume       = {{113}},
  year         = {{2026}},
}

@article{64877,
  author       = {{Taheri, Behnood and Kopylov, Denis and Hammer, Manfred and Meier, Torsten and Förstner, Jens and Sharapova, Polina R.}},
  journal      = {{arXiv}},
  title        = {{{Gain-induced spectral non-degeneracy in type-II parametric down-conversion}}},
  doi          = {{10.48550/ARXIV.2603.01656}},
  year         = {{2026}},
}

@article{63744,
  abstract     = {{Orbital angular momentum (OAM) modes are an important resource used in various branches of quantum science and technology due to their unique helical structure and countably infinite basis. Generating light that simultaneously carries high-order orbital angular momenta and exhibits quantum correlations is a challenging task. In this work, we present a theoretical approach to the generation of correlated Schmidt modes carrying OAM via parametric down-conversion (PDC) in cascaded nonlinear systems (nonlinear interferometers) pumped by Laguerre–Gaussian beams. We demonstrate how the number of generated modes and their population can be controlled by varying the pump parameters, the gain of the PDC process, and the distance between the crystals. We investigate the angular displacement measurement uncertainty of these interferometers and demonstrate that it can overcome the classical shot noise limit.}},
  author       = {{Scharwald, Dennis and Gehse, Lucas and Sharapova, Polina}},
  issn         = {{2378-0967}},
  journal      = {{APL Photonics}},
  number       = {{1}},
  publisher    = {{AIP Publishing}},
  title        = {{{Schmidt modes carrying orbital angular momentum generated by cascaded systems pumped with Laguerre–Gaussian beams}}},
  doi          = {{10.1063/5.0229802}},
  volume       = {{10}},
  year         = {{2025}},
}

@article{63745,
  abstract     = {{Multimode squeezed light is an increasingly popular tool in photonic quantum technologies, including sensing, imaging, and computation. Meanwhile, the existing methods of its characterization are technically complicated, which reduces the level of squeezing, and mostly deal with a single mode at a time. Here, for the first time, to the best of our knowledge, we employ optical parametric amplification to characterize multiple squeezing eigenmodes simultaneously. We retrieve the shapes and squeezing degrees of all modes at once through direct detection followed by modal decomposition. This method is tolerant to inefficient detection and does not require a local oscillator. For a spectrally and spatially multimode squeezed vacuum, we characterize eight strongest spatial modes, obtaining squeezing and anti-squeezing values of up to −5.2 ± 0.2 dB and 8.6 ± 0.3 dB, respectively, despite the 50% detection loss. This work, being the first exploration of an optical parametric amplifier’s multimode capability for squeezing detection, paves the way for the real-time detection of multimode squeezing.}},
  author       = {{Barakat, Ismail and Kalash, Mahmoud and Scharwald, Dennis and Sharapova, Polina and Lindlein, Norbert and Chekhova, Maria}},
  issn         = {{2837-6714}},
  journal      = {{Optica Quantum}},
  number       = {{1}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Simultaneous measurement of multimode squeezing through multimode phase-sensitive amplification}}},
  doi          = {{10.1364/opticaq.524682}},
  volume       = {{3}},
  year         = {{2025}},
}

@article{61245,
  author       = {{Barkhausen, Franziska and Ares Santos, Laura and Schumacher, Stefan and Sperling, Jan}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{3}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Entanglement between dependent degrees of freedom: Quasiparticle correlations}}},
  doi          = {{10.1103/physreva.111.032404}},
  volume       = {{111}},
  year         = {{2025}},
}

@article{62911,
  abstract     = {{<jats:p>In this paper, we theoretically study the spectral and temporal properties of pulsed spontaneous parametric down-conversion (SPDC) generated in lossy waveguides. Our theoretical approach is based on the formalism of Gaussian states and the Langevin equation, which is elaborated for weak parametric down-conversion and photon-number-unresolved click detection. Using the example of frequency-degenerate type-II SPDC generated under the pump-idler group-velocity-matching condition, we show how the joint-spectral intensity, mode structure, normalized second-order correlation function, and Hong-Ou-Mandel interference pattern depend on internal losses of the SPDC process. We found that the joint-spectral intensity is almost insensitive to internal losses, while the second-order correlation function shows a strong dependence on them, being different for the signal and idler beams in the presence of internal losses. Based on the sensitivity of the normalized second-order correlation function, we show how its measurement can be used to experimentally determine internal losses.</jats:p>}},
  author       = {{Kopylov, Denis A. and Stefszky, Michael and Meier, Torsten and Silberhorn, Christine and Sharapova, Polina R.}},
  issn         = {{2643-1564}},
  journal      = {{Physical Review Research}},
  number       = {{3}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Spectral and temporal properties of type-II parametric down-conversion: The impact of losses during state generation}}},
  doi          = {{10.1103/zp72-7qwl}},
  volume       = {{7}},
  year         = {{2025}},
}

@article{60992,
  abstract     = {{Non-Hermitian systems hosting exceptional points (EPs) exhibit enhanced sensitivity and unconventional mode dynamics. Going beyond isolated EPs, here we report on the existence of exceptional rings (ERs) in planar optical resonators with specific form of circular dichroism and TE-TM splitting. Such exceptional rings possess intriguing topologies as discussed earlier for condensed matter systems, but they remain virtually unexplored in presence of nonlinearity, for which our photonic platform is ideal. We find that when Kerr-type nonlinearity (or saturable gain) is introduced, the linear ER splits into two concentric ERs, with the larger-radius ring being a ring of third-order EPs. Transitioning from linear to nonlinear regime, we present a rigorous analysis of spectral topology and report enhanced and adjustable perturbation response in the nonlinear regime. Whereas certain features are specific to our system, the results on non-Hermitian spectral topology and nonlinearity-enhanced perturbation response are generic and equally relevant to a broad class of other nonlinear non-Hermitian systems, providing a universal framework for engineering ERs and EPs in nonlinear non-Hermitian systems.}},
  author       = {{Wingenbach, Jan and Ares Santos, Laura  and Ma, Xuekai and Sperling, Jan and Schumacher, Stefan}},
  journal      = {{Arxiv}},
  publisher    = {{Arxiv}},
  title        = {{{Sensitivity and Topology of Exceptional Rings in Nonlinear Non-Hermitian Planar Optical Microcavities}}},
  doi          = {{10.48550/ARXIV.2507.07099}},
  year         = {{2025}},
}

@article{62980,
  abstract     = {{<jats:p>We introduce a new classification of multimode states with a fixed number of photons. This classification is based on the factorizability of homogeneous multivariate polynomials and is invariant under unitary transformations. The classes physically correspond to field excitations in terms of single and multiple photons, each of which is in an arbitrary irreducible superposition of quantized modes. We further show how the transitions between classes are rendered possible by photon addition, photon subtraction, and photon-projection nonlinearities. We explicitly put forward a design for a multilayer interferometer in which the states for different classes can be generated with state-of-the-art experimental techniques. Limitations of the proposed designs are analyzed using the introduced classification, providing a benchmark for the robustness of certain states and classes.</jats:p>}},
  author       = {{Kopylov, Denis A. and Offen, Christian and Ares, Laura and Wembe Moafo, Boris Edgar and Ober-Blöbaum, Sina and Meier, Torsten and Sharapova, Polina R. and Sperling, Jan}},
  issn         = {{2643-1564}},
  journal      = {{Physical Review Research}},
  number       = {{3}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Multiphoton, multimode state classification for nonlinear optical circuits}}},
  doi          = {{10.1103/sv6z-v1gk}},
  volume       = {{7}},
  year         = {{2025}},
}

@unpublished{62979,
  abstract     = {{We introduce a new classification of multimode states with a fixed number of photons. This classification is based on the factorizability of homogeneous multivariate polynomials and is invariant under unitary transformations. The classes physically correspond to field excitations in terms of single and multiple photons, each of which being in an arbitrary irreducible superposition of quantized modes. We further show how the transitions between classes are rendered possible by photon addition, photon subtraction, and photon-projection nonlinearities. We explicitly put forward a design for a multilayer interferometer in which the states for different classes can be generated with state-of-the-art experimental techniques. Limitations of the proposed designs are analyzed using the introduced classification, providing a benchmark for the robustness of certain states and classes.}},
  author       = {{Meier, Torsten and Sharapova, Polina R. and Sperling, Jan and Ober-Blöbaum, Sina and Wembe Moafo, Boris Edgar and Offen, Christian}},
  title        = {{{Multiphoton, multimode state classification for nonlinear optical circuits}}},
  year         = {{2025}},
}

@article{63562,
  abstract     = {{<jats:p>Entangled two-mode Gaussian states constitute an important building block for continuous variable quantum computing and communication protocols. In this work, we theoretically study two-mode bipartite states, which are extracted from multimode light generated via type-II parametric downconversion (PDC) in lossy waveguides. For these states, we demonstrate that the squeezing quantifies entanglement and we construct a measurement basis, which results in the maximal bipartite entanglement. We illustrate our findings by numerically solving the spatial master equation for PDC in a Markovian environment. The optimal measurement modes are compared with two widely used broadband bases: the Mercer–Wolf basis (the first-order coherence basis) and the Williamson–Euler basis.</jats:p>}},
  author       = {{Kopylov, Denis and Meier, Torsten and Sharapova, Polina R.}},
  issn         = {{2835-0103}},
  journal      = {{APL Quantum}},
  number       = {{4}},
  publisher    = {{AIP Publishing}},
  title        = {{{Bipartite entanglement extracted from multimode squeezed light generated in lossy waveguides}}},
  doi          = {{10.1063/5.0293116}},
  volume       = {{2}},
  year         = {{2025}},
}

@article{55140,
  author       = {{Yasmin, Farha and Sperling, Jan}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{1}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Entanglement-assisted quantum speedup: Beating local quantum speed limits}}},
  doi          = {{10.1103/physreva.110.012424}},
  volume       = {{110}},
  year         = {{2024}},
}

@inbook{62916,
  author       = {{Zhang, Hongdan and Zuo, Ruixin and Yang, Shidong and Trautmann, Alexander and Song, Xiaohong and Meier, Torsten and Yang, Weifeng}},
  booktitle    = {{High-Order Harmonic Generation in Solids}},
  isbn         = {{9789811279553}},
  publisher    = {{WORLD SCIENTIFIC}},
  title        = {{{Analyzing High-Order Harmonic Generation in Solids Based on Semi-Classical Recollision Models}}},
  doi          = {{10.1142/9789811279560_0006}},
  year         = {{2024}},
}

@inbook{62917,
  author       = {{Reichelt, Matthias and Zuo, Ruixin and Song, Xiaohong and Yang, Weifeng and Meier, Torsten}},
  booktitle    = {{High-Order Harmonic Generation in Solids}},
  isbn         = {{9789811279553}},
  publisher    = {{WORLD SCIENTIFIC}},
  title        = {{{High-Order Harmonic Generation in Semiconductors with Excitonic Effects}}},
  doi          = {{10.1142/9789811279560_0009}},
  year         = {{2024}},
}

@article{44050,
  author       = {{Sperling, Jan and Agudelo, Elizabeth}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{4}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Entanglement of particles versus entanglement of fields: Independent quantum resources}}},
  doi          = {{10.1103/physreva.107.042420}},
  volume       = {{107}},
  year         = {{2023}},
}

@article{42973,
  author       = {{Lüders, Carolin and Pukrop, Matthias and Barkhausen, Franziska and Rozas, Elena and Schneider, Christian and Höfling, Sven and Sperling, Jan and Schumacher, Stefan and Aßmann, Marc}},
  issn         = {{0031-9007}},
  journal      = {{Physical Review Letters}},
  keywords     = {{General Physics and Astronomy}},
  number       = {{11}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Tracking Quantum Coherence in Polariton Condensates with Time-Resolved Tomography}}},
  doi          = {{10.1103/physrevlett.130.113601}},
  volume       = {{130}},
  year         = {{2023}},
}

@article{55900,
  author       = {{Scharwald, Dennis and Meier, Torsten and Sharapova, Polina}},
  issn         = {{2643-1564}},
  journal      = {{Physical Review Research}},
  number       = {{4}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Phase sensitivity of spatially broadband high-gain SU(1,1) interferometers}}},
  doi          = {{10.1103/physrevresearch.5.043158}},
  volume       = {{5}},
  year         = {{2023}},
}

@inproceedings{40386,
  author       = {{Sharapova, Polina and Luo, Kai Hong and Herrmann, Harald and Reichelt, Matthias and Silberhorn, Christine and Meier, Torsten}},
  booktitle    = {{Conference on Lasers and Electro-Optics}},
  isbn         = {{978-1-943580-42-2}},
  location     = {{San Jose, California United States}},
  publisher    = {{OSA}},
  title        = {{{Manipulation of Two-Photon Interference by Entanglement}}},
  doi          = {{10.1364/cleo_qels.2018.ff1b.8}},
  year         = {{2018}},
}