@article{65359,
  abstract     = {{<jats:p>Lithium niobate sees widespread use in nonlinear and quantum optical devices, such as for sum- and difference-frequency generation or spontaneous parametric downconversion. In lithium niobate waveguides, nonlinear optical processes are often limited by the so-called photorefractive effect, which limits the maximum input or output powers and impacts the nonlinear spectral response. Therefore, strategies for the management of photorefractive damage are a key consideration in device design. Usually, the photorefractive damage threshold, i.e., the maximal permissible operating power, can be increased by high-temperature operation of devices. This approach, however, is not applicable in cryogenic environments, which may be required for specialized applications. To better understand the impact of photorefraction in nonlinear optical applications, we study the impact of photorefraction on the phase-matching spectra of two nonlinear-optical sum-frequency generation experiments at (1) high temperatures and (2) cryogenic temperatures. Furthermore, we present an approach to reduce the impact of photorefraction, which is compatible with cryogenic operation. This comprises an auxiliary light source, propagating in the same waveguide, which is used to restore phase-matching spectra impacted by photorefraction, as well as reduce pyroelectric effects. Our work provides an alternative route to photorefraction management applicable to cryogenic environments, as well as in situations with tight energy budgets, such as space applications.</jats:p>}},
  author       = {{Lange, Nina Amelie and Pollmann, René and Rüsing, Michael and Stefszky, Michael and Protte, Maximilian and Ricken, Raimund and Padberg, Laura and Eigner, Christof and Bartley, Tim and Silberhorn, Christine}},
  issn         = {{0021-8979}},
  journal      = {{Journal of Applied Physics}},
  number       = {{13}},
  publisher    = {{AIP Publishing}},
  title        = {{{Photorefraction management in lithium niobate waveguides: High-temperature vs cryogenic solutions}}},
  doi          = {{10.1063/5.0324002}},
  volume       = {{139}},
  year         = {{2026}},
}

@article{62269,
  abstract     = {{The titanium in-diffused lithium niobate waveguide platform is well-established for reliable prototyping and packaging of many quantum photonic components at room temperature. Nevertheless, compatibility with certain quantum light sources and superconducting detectors requires operation under cryogenic conditions. We characterize alterations in phase-matching and mode guiding of a non-degenerate spontaneous parametric down-conversion process emitting around 1556 nm and 950 nm, under cryogenic conditions. Despite the effects of pyroelectricity and photorefraction, the spectral properties match our theoretical model. Nevertheless, these effects cause small but significant variations within and between cooling cycles. These measurements provide a first benchmark against which other nonlinear photonic integration platforms, such as thin-film lithium niobate, can be compared.}},
  author       = {{Lange, Nina Amelie and Lengeling, Sebastian and Mues, Philipp and Quiring, Viktor and Ridder, Werner and Eigner, Christof and Herrmann, Harald and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{24}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Widely non-degenerate nonlinear frequency conversion in cryogenic titanium in-diffused lithium niobate waveguides}}},
  doi          = {{10.1364/oe.578108}},
  volume       = {{33}},
  year         = {{2025}},
}

@article{60466,
  author       = {{Brockmeier, Julian and Schapeler, Timon and Lange, Nina Amelie and Höpker, Jan Philipp and Herrmann, Harald and Silberhorn, Christine and Bartley, Tim}},
  journal      = {{New Journal of Physics}},
  title        = {{{Harnessing temporal dispersion for integrated pump filtering in spontaneous heralded single-photon generation processes}}},
  doi          = {{10.1088/1367-2630/ade46c}},
  year         = {{2025}},
}

@article{60136,
  abstract     = {{<jats:p>Modulation conditioned on measurements on entangled photonic quantum states is a cornerstone technology of optical quantum information processing. Performing this task with low latency requires combining single-photon-level detectors with both electronic logic processing and optical modulation in close proximity. Here, we demonstrate low-latency feedforward using a quasi-photon-number-resolved measurement on a quantum light source. Specifically, we use a multipixel superconducting nanowire single-photon detector, amplifier, logic, and an integrated electro-optic modulator <jats:italic toggle="yes">in situ</jats:italic> below 4 K. We modulate the signal mode of a spontaneous parametric down-conversion source, conditional on a photon-number measurement of the idler mode, with a total latency of (23±3)ns. Furthermore, we investigate the resulting change in the photon statistics. This represents an important benchmark for the fastest quantum photonic feedforward experiments comprising measurement, amplification, logic, and modulation. This has direct applications in quantum computing, communication, and simulation protocols.</jats:p>}},
  author       = {{Thiele, Frederik and Lamberty, Niklas and Hummel, Thomas and Lange, Nina Amelie and Procopio Peña, Lorenzo Manuel and Barua, Aishi and Lengeling, Sebastian and Quiring, Viktor and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{2334-2536}},
  journal      = {{Optica}},
  number       = {{5}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Cryogenic feedforward of a photonic quantum state}}},
  doi          = {{10.1364/optica.551287}},
  volume       = {{12}},
  year         = {{2025}},
}

@article{51356,
  abstract     = {{<jats:title>Abstract</jats:title>
               <jats:p>Lithium niobate has emerged as a promising platform for integrated quantum optics, enabling efficient generation, manipulation, and detection of quantum states of light. However, integrating single-photon detectors requires cryogenic operating temperatures, since the best performing detectors are based on narrow superconducting wires. While previous studies have demonstrated the operation of quantum light sources and electro-optic modulators in LiNbO<jats:sub>3</jats:sub> at cryogenic temperatures, the thermal transition between room temperature and cryogenic conditions introduces additional effects that can significantly influence device performance. In this paper, we investigate the generation of pyroelectric charges and their impact on the optical properties of lithium niobate waveguides when changing from room temperature to 25 K, and vice versa. We measure the generated pyroelectric charge flow and correlate this with fast changes in the birefringence acquired through the Sénarmont-method. Both electrical and optical influence of the pyroelectric effect occur predominantly at temperatures above 100 K.</jats:p>}},
  author       = {{Thiele, Frederik and Hummel, Thomas and Lange, Nina Amelie and Dreher, Felix and Protte, Maximilian and Bruch, Felix vom and Lengeling, Sebastian and Herrmann, Harald and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{2633-4356}},
  journal      = {{Materials for Quantum Technology}},
  keywords     = {{General Earth and Planetary Sciences, General Environmental Science}},
  number       = {{1}},
  publisher    = {{IOP Publishing}},
  title        = {{{Pyroelectric influence on lithium niobate during the thermal transition for cryogenic integrated photonics}}},
  doi          = {{10.1088/2633-4356/ad207d}},
  volume       = {{4}},
  year         = {{2024}},
}

@article{46468,
  author       = {{Lange, Nina Amelie and Schapeler, Timon and Höpker, Jan Philipp and Protte, Maximilian and Bartley, Tim}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{2}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Degenerate photons from a cryogenic spontaneous parametric down-conversion source}}},
  doi          = {{10.1103/physreva.108.023701}},
  volume       = {{108}},
  year         = {{2023}},
}

@article{30342,
  author       = {{Lange, Nina Amelie and Höpker, Jan Philipp and Ricken, Raimund and Quiring, Viktor and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{2334-2536}},
  journal      = {{Optica}},
  keywords     = {{Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}},
  number       = {{1}},
  publisher    = {{The Optical Society}},
  title        = {{{Cryogenic integrated spontaneous parametric down-conversion}}},
  doi          = {{10.1364/optica.445576}},
  volume       = {{9}},
  year         = {{2022}},
}