@article{59069,
  abstract     = {{<jats:p>Stable and bright single photon sources are key components for future quantum applications. A simple fabrication method is an important requirement for such sources. Here, we present a single photon source based on diced ridge waveguides in titanium indiffused LiNbO<jats:sub>3</jats:sub>. These waveguides can be easily fabricated by combining planar titanium in-diffusion without lithographic patterning and easy-to-handle precision dicing. Such devices have the potential to generate high single photon rates because ridge structures are typically less prone to the photorefractive effect. We achieve waveguide propagation losses &lt;0.4dBcm and a SHG conversion efficiency of about 81%Wcm<jats:sup>2</jats:sup>. Harnessing a type-0 SPDC process to generate 1550 nm photons, we obtain a SPDC brightness of 3⋅10<jats:sup>5</jats:sup>1s⋅mW⋅nm, with a heralding efficiency of <jats:italic>η</jats:italic><jats:sub>h</jats:sub>=45% (<jats:italic>η</jats:italic><jats:sub>h,wg</jats:sub>=77.5% for the waveguide itself excluded setup losses) and a heralded second-order correlation function of <jats:italic>g</jats:italic><jats:sub>h</jats:sub><jats:sup>2</jats:sup>(0)&lt;0.003 at low pump powers.</jats:p>}},
  author       = {{Kießler, Christian and Kirsch, Michelle and Lengeling, Sebastian and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{2770-0208}},
  journal      = {{Optics Continuum}},
  number       = {{3}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{SPDC single-photon source in Ti-indiffused diced ridge LiNbO<sub>3</sub> waveguides}}},
  doi          = {{10.1364/optcon.557439}},
  volume       = {{4}},
  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{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{63192,
  abstract     = {{Lithium niobate (LiNbO3) is a widely used material with several desirable physical properties, such as high second-order nonlinear optical and strong electro-optical effects. Thus LiNbO3 is used for various applications such as electro-optic modulation or nonlinear frequency conversion and mixing. But LiNbO3 also exhibits a strong photorefractive effect, which limits the intensity of the optical fields involved. Various approaches to reduce the photorefractive effect have been investigated, such as increasing the temperature, doping the crystal or using different waveguide designs in LiNbO3. Here, we present an analysis of the approach to increase the photorefractive damage threshold by using different waveguide designs. Contrary to previous claims and investigations, our SHG measurements revealed no significant difference in resistance to photorefractive damage when comparing conventional Ti-doped channel waveguides and Ti-doped diced ridge waveguides in LiNbO3. Furthermore, we have investigated the effect of photorefractive cleaning and curing using a light field at 532 nm. Here, we observe a reduction in the photorefractive effect at room temperature during and after SHG measurements, which is an easy alternative to conventional approaches.}},
  author       = {{Kirsch, Michelle and Kießler, Christian and Lengeling, Sebastian and Stefszky, Michael and Eigner, Christof and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{0030-3992}},
  journal      = {{Optics & Laser Technology}},
  publisher    = {{Elsevier BV}},
  title        = {{{Photorefraction and in-situ optical cleaning in various types of LiNbO3 waveguides}}},
  doi          = {{10.1016/j.optlastec.2025.114260}},
  volume       = {{193}},
  year         = {{2025}},
}

@article{60566,
  author       = {{Bocchini, Adriana and Rüsing, Michael and Bollmers, Laura and Lengeling, Sebastian and Mues, Philipp and Padberg, Laura and Gerstmann, Uwe and Silberhorn, Christine and Eigner, Christof and Schmidt, Wolf Gero}},
  issn         = {{2475-9953}},
  journal      = {{Physical Review Materials}},
  number       = {{7}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Mg dopants in lithium niobate: Defect models and impact on domain inversion}}},
  doi          = {{10.1103/5wz1-bjyr}},
  volume       = {{9}},
  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{48399,
  abstract     = {{<jats:p>Quantum photonic processing via electro-optic components typically requires electronic links across different operation environments, especially when interfacing cryogenic components such as superconducting single photon detectors with room-temperature control and readout electronics. However, readout and driving electronics can introduce detrimental parasitic effects. Here we show an all-optical control and readout of a superconducting nanowire single photon detector (SNSPD), completely electrically decoupled from room temperature electronics. We provide the operation power for the superconducting detector via a cryogenic photodiode, and readout single photon detection signals via a cryogenic electro-optic modulator in the same cryostat. This method opens the possibility for control and readout of superconducting circuits, and feedforward for photonic quantum computing.</jats:p>}},
  author       = {{Thiele, Frederik and Hummel, Thomas and McCaughan, Adam N. and Brockmeier, Julian and Protte, Maximilian and Quiring, Victor and Lengeling, Sebastian and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{20}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{All optical operation of a superconducting photonic interface}}},
  doi          = {{10.1364/oe.492035}},
  volume       = {{31}},
  year         = {{2023}},
}

@article{33672,
  abstract     = {{<jats:title>Abstract</jats:title>
               <jats:p>Lithium niobate is a promising platform for integrated quantum optics. In this platform, we aim to efficiently manipulate and detect quantum states by combining superconducting single photon detectors and modulators. The cryogenic operation of a superconducting single photon detector dictates the optimisation of the electro-optic modulators under the same operating conditions. To that end, we characterise a phase modulator, directional coupler, and polarisation converter at both ambient and cryogenic temperatures. The operation voltage <jats:inline-formula>
                     <jats:tex-math><?CDATA $V_{\pi/2}$?></jats:tex-math>
                     <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                        <mml:msub>
                           <mml:mi>V</mml:mi>
                           <mml:mrow>
                              <mml:mi>π</mml:mi>
                              <mml:mrow>
                                 <mml:mo>/</mml:mo>
                              </mml:mrow>
                              <mml:mn>2</mml:mn>
                           </mml:mrow>
                        </mml:msub>
                     </mml:math>
                     <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn1.gif" xlink:type="simple" />
                  </jats:inline-formula> of these modulators increases, due to the decrease in the electro-optic effect, by 74% for the phase modulator, 84% for the directional coupler and 35% for the polarisation converter below 8.5<jats:inline-formula>
                     <jats:tex-math><?CDATA $\,\mathrm{K}$?></jats:tex-math>
                     <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                        <mml:mrow>
                           <mml:mi mathvariant="normal">K</mml:mi>
                        </mml:mrow>
                     </mml:math>
                     <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn2.gif" xlink:type="simple" />
                  </jats:inline-formula>. The phase modulator preserves its broadband nature and modulates light in the characterised wavelength range. The unbiased bar state of the directional coupler changed by a wavelength shift of 85<jats:inline-formula>
                     <jats:tex-math><?CDATA $\,\mathrm{nm}$?></jats:tex-math>
                     <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                        <mml:mrow>
                           <mml:mi mathvariant="normal">n</mml:mi>
                           <mml:mi mathvariant="normal">m</mml:mi>
                        </mml:mrow>
                     </mml:math>
                     <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn3.gif" xlink:type="simple" />
                  </jats:inline-formula> while cooling the device down to 5<jats:inline-formula>
                     <jats:tex-math><?CDATA $\,\mathrm{K}$?></jats:tex-math>
                     <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                        <mml:mrow>
                           <mml:mi mathvariant="normal">K</mml:mi>
                        </mml:mrow>
                     </mml:math>
                     <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn4.gif" xlink:type="simple" />
                  </jats:inline-formula>. The polarisation converter uses periodic poling to phasematch the two orthogonal polarisations. The phasematched wavelength of the utilised poling changes by 112<jats:inline-formula>
                     <jats:tex-math><?CDATA $\,\mathrm{nm}$?></jats:tex-math>
                     <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                        <mml:mrow>
                           <mml:mi mathvariant="normal">n</mml:mi>
                           <mml:mi mathvariant="normal">m</mml:mi>
                        </mml:mrow>
                     </mml:math>
                     <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn5.gif" xlink:type="simple" />
                  </jats:inline-formula> when cooling to 5<jats:inline-formula>
                     <jats:tex-math><?CDATA $\,\mathrm{K}$?></jats:tex-math>
                     <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                        <mml:mrow>
                           <mml:mi mathvariant="normal">K</mml:mi>
                        </mml:mrow>
                     </mml:math>
                     <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn6.gif" xlink:type="simple" />
                  </jats:inline-formula>.</jats:p>}},
  author       = {{Thiele, Frederik and vom Bruch, Felix and Brockmeier, Julian and Protte, Maximilian and Hummel, Thomas and Ricken, Raimund and Quiring, Viktor and Lengeling, Sebastian and Herrmann, Harald and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{2515-7647}},
  journal      = {{Journal of Physics: Photonics}},
  keywords     = {{Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}},
  number       = {{3}},
  publisher    = {{IOP Publishing}},
  title        = {{{Cryogenic electro-optic modulation in titanium in-diffused lithium niobate waveguides}}},
  doi          = {{10.1088/2515-7647/ac6c63}},
  volume       = {{4}},
  year         = {{2022}},
}

@inproceedings{13903,
  author       = {{Höpker, Jan Philipp and Bartnick, Moritz and Meyer-Scott, Evan and Thiele, Frederik and Meier, Torsten and Bartley, Tim and Krapick, Stephan and Montaut, Nicola M. and Santandrea, Matteo and Herrmann, Harald and Lengeling, Sebastian and Ricken, Raimund and Quiring, Viktor and Lita, Adriana E. and Verma, Varun B. and Gerrits, Thomas and Nam, Sae Woo and Silberhorn, Christine}},
  booktitle    = {{Quantum Photonic Devices}},
  editor       = {{Agio, Mario and Srinivasan, Kartik and Soci, Cesare}},
  isbn         = {{9781510611733}},
  pages        = {{1035809}},
  publisher    = {{SPIE}},
  title        = {{{Towards integrated superconducting detectors on lithium niobate waveguides}}},
  doi          = {{10.1117/12.2273388}},
  volume       = {{10358}},
  year         = {{2017}},
}