@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}},
}

@inproceedings{47534,
  abstract     = {{In this proceeding we consider a translation invariant Nelson type model in
two spatial dimensions modeling a scalar relativistic particle in interaction
with a massive radiation field. As is well-known, the corresponding Hamiltonian
can be defined with the help of an energy renormalization. First, we review a
Feynman-Kac formula for the semigroup generated by this Hamiltonian proven by
the authors in a recent preprint (where several matter particles and exterior
potentials are treated as well). After that, we employ a few technical key
relations and estimates obtained in our preprint to present an otherwise
self-contained derivation of new Feynman-Kac formulas for the fiber
Hamiltonians attached to fixed total momenta of the translation invariant
system. We conclude by inferring an alternative derivation of the Feynman-Kac
formula for the full translation invariant Hamiltonian.}},
  author       = {{Hinrichs, Benjamin and Matte, Oliver}},
  booktitle    = {{Proceedings of the 2023 RIMS Workshop 'Mathematical Aspects of Quantum Fields and Related Topics'}},
  editor       = {{Hiroshima, Fumio}},
  number       = {{3}},
  title        = {{{Feynman-Kac formula for fiber Hamiltonians in the relativistic Nelson  model in two spatial dimensions}}},
  volume       = {{2310}},
  year         = {{2025}},
}

@unpublished{63642,
  abstract     = {{We prove absence of ground states in the infrared-divergent spin boson model at large coupling. Our key argument reduces the proof to verifying long range order in the dual one-dimensional continuum Ising model, i.e., to showing that the respective two point function is lower bounded by a strictly positive constant. We can then use known results from percolation theory to establish long range order at large coupling. Combined with the known existence of ground states at small coupling, our result proves that the spin boson model undergoes a phase transition with respect to the coupling strength. We also present an expansion for the vacuum overlap of the spin boson ground state in terms of the Ising $n$-point functions, which implies that the phase transition is unique, i.e., that there is a critical coupling constant below which a ground state exists and above which none can exist.}},
  author       = {{Betz, Volker and Hinrichs, Benjamin and Kraft, Mino Nicola and Polzer, Steffen}},
  booktitle    = {{arXiv:2501.19362}},
  title        = {{{On the Ising Phase Transition in the Infrared-Divergent Spin Boson Model}}},
  year         = {{2025}},
}

@unpublished{63644,
  abstract     = {{We study the ultraviolet problem for models of a finite-dimensional quantum mechanical system linearly coupled to a bosonic quantum field, such as the (many-)spin boson model or its rotating-wave approximation. If the state change of the system upon emission or absorption of a boson is either given by a normal matrix or by a 2-nilpotent one, which is the case for the previously named examples, we prove an optimal renormalization result. We complement it, by proving the norm resolvent convergence of appropriately regularized models to the renormalized one. Our method consists of a dressing transformation argument in the normal case and an appropriate interior boundary condition for the 2-nilpotent case.}},
  author       = {{Hinrichs, Benjamin and Lampart, Jonas and Valentín Martín, Javier}},
  booktitle    = {{arXiv:2502.04876}},
  title        = {{{Ultraviolet Renormalization of Spin Boson Models I. Normal and 2-Nilpotent Interactions}}},
  year         = {{2025}},
}

@unpublished{63645,
  abstract     = {{In this paper we construct the non-trivial, renormalized Hamiltonian for a class of spin-boson models with supercritical form factors, including the one describing the Weisskopf-Wigner spontaneous emission. The renormalization is performed through both a self-energy and mass renormalization, in the so-called Hamiltonian formalism of constructive quantum field theory, implemented by a non-unitary dressing transformation. This solves the problem of triviality for unitarily-renormalized supercritical spin-boson models.}},
  author       = {{Falconi, Marco and Hinrichs, Benjamin and Valentín Martín, Javier}},
  booktitle    = {{arXiv:2508.00805}},
  title        = {{{Non-Trivial Renormalization of Spin-Boson Models with Supercritical Form Factors}}},
  year         = {{2025}},
}

@unpublished{63646,
  abstract     = {{We study the behavior of a probability measure near the bottom of its support in terms of time averaged quotients of its Laplace transform. We discuss how our results are connected to both rank-one perturbation theory as well as renewal theory. We further apply our results in order to derive criteria for the existence and non-existence of ground states for a finite dimensional quantum system coupled to a bosonic field.}},
  author       = {{Hinrichs, Benjamin and Polzer, Steffen}},
  booktitle    = {{arXiv:2511.02867}},
  title        = {{{Wiener-Type Theorems for the Laplace Transform. With Applications to Ground State Problems}}},
  year         = {{2025}},
}

@unpublished{63647,
  abstract     = {{We study the convergence rate of translation-invariant discrete-time quantum dynamics on a one-dimensional lattice. We prove that the cumulative distributions function of the ballistically scaled position $\mathbb X(n)/{n}$ after $n$ steps converges at a rate of $n^{-1/3}$ in the Lévy metric as $n\to\infty$. In the special case of step-coin quantum walks with two-dimensional coin space, we recover the same convergence rate for the supremum distance and prove optimality.}},
  author       = {{Hinrichs, Benjamin and Mittenbühler, Pascal}},
  booktitle    = {{arXiv:2511.13409}},
  title        = {{{On the Optimal Rate of Convergence for Translation-Invariant 1D Quantum Walks}}},
  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{58519,
  abstract     = {{<jats:p>A unified theoretical approach to describe the properties of multimode squeezed light generated in a lossy medium is presented. This approach is valid for Markovian environments and includes both a model of discrete losses based on the beamsplitter approach and a generalized continuous loss model based on the spatial Langevin equation. For an important class of Gaussian states, we derive master equations for the second-order correlation functions and illustrate their solution for both frequency-independent and frequency-dependent losses. Studying the mode structure, we demonstrate that in a lossy environment no broadband basis without quadrature correlations between the different broadband modes exists. Therefore, various techniques and strategies to introduce broadband modes can be considered. We show that the Mercer expansion and the Williamson-Euler decomposition do not provide modes in which the maximal squeezing contained in the system can be measured. In turn, we find a new broadband basis that maximizes squeezing in the lossy system and present an algorithm to construct it.</jats:p>}},
  author       = {{Kopylov, Denis A. and Meier, Torsten and Sharapova, Polina R.}},
  issn         = {{2521-327X}},
  journal      = {{Quantum}},
  publisher    = {{Verein zur Forderung des Open Access Publizierens in den Quantenwissenschaften}},
  title        = {{{Theory of Multimode Squeezed Light Generation in Lossy Media}}},
  doi          = {{10.22331/q-2025-02-04-1621}},
  volume       = {{9}},
  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}},
}

@inproceedings{62913,
  author       = {{Hunstig, Anna and Peitz, Sebastian and Rose, Hendrik and Meier, Torsten}},
  booktitle    = {{2024 IEEE 63rd Conference on Decision and Control (CDC)}},
  publisher    = {{IEEE}},
  title        = {{{Accelerating the analysis of optical quantum systems using the Koopman operator}}},
  doi          = {{10.1109/cdc56724.2024.10886589}},
  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{63160,
  author       = {{Rose, Hendrik and Schumacher, Stefan and Meier, Torsten}},
  issn         = {{2469-9950}},
  journal      = {{Physical Review B}},
  number       = {{24}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Microscopic approach to the quantized light-matter interaction in semiconductor nanostructures: Complex coupled dynamics of excitons, biexcitons, and photons}}},
  doi          = {{10.1103/528f-7smh}},
  volume       = {{112}},
  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{51339,
  author       = {{Babai-Hemati, Jonas and vom Bruch, Felix and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Tailored second harmonic generation inTi-diffused PPLN waveguides usingmicro-heaters}}},
  doi          = {{10.1364/oe.510319}},
  year         = {{2024}},
}

@article{55173,
  author       = {{Di Fidio, Christian and Ares, Laura and Sperling, Jan}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{1}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Quantum walks and entanglement in cavity networks}}},
  doi          = {{10.1103/physreva.110.013705}},
  volume       = {{110}},
  year         = {{2024}},
}

@article{54668,
  abstract     = {{Samples of dielectric optical waveguides of rib or strip type in thin-film lithium niobate (TFLN) technology are characterized with respect to their optical loss using the Fabry-Pérot method. Attributing the losses mainly to sidewall roughness, we employ a simple perturbational procedure, based on rigorously computed mode profiles of idealized channels, to estimate the attenuation for waveguides with different cross sections. A single fit parameter suffices for an adequate modelling of the effect of the waveguide geometry on the loss levels.}},
  author       = {{Hammer, Manfred and Babel, Silia and Farheen, Henna and Padberg, Laura and Scheytt, J. Christoph and Silberhorn, Christine and Förstner, Jens}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{tet_topic_waveguide}},
  number       = {{13}},
  pages        = {{22878}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Estimation of losses caused by sidewall roughness in thin-film lithium niobate rib and strip waveguides}}},
  doi          = {{10.1364/oe.521766}},
  volume       = {{32}},
  year         = {{2024}},
}

@article{55751,
  abstract     = {{Lateral leakage of TM modes in dielectric optical waveguides of rib/ridge or strip-loaded types can be fully suppressed, if the waveguide core is formed not through a strip that protrudes at one side (up) from the remaining lateral guiding slab, but through parallel strips on both sides (up and down), such that the resulting cross section becomes vertically symmetric. The fairly general arguments underlying the leakage suppression apply to TM modes of all orders simultaneously, and are independent of wavelength. These plus-shaped waveguides support strictly guided, non-leaky TM modes for, in principle, arbitrarily shallow etching.}},
  author       = {{Üstün, Necati and Farheen, Henna and Hammer, Manfred and Förstner, Jens}},
  issn         = {{0740-3224}},
  journal      = {{Journal of the Optical Society of America B}},
  keywords     = {{tet_topic_waveguide}},
  number       = {{9}},
  pages        = {{2077}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Symmetry-protected TM modes in rib-like, plus-shaped optical waveguides with shallow etching}}},
  doi          = {{10.1364/josab.528729}},
  volume       = {{41}},
  year         = {{2024}},
}