@article{63451,
abstract = {{Superconducting nanowire single-photon detectors (SNSPDs) can enable photon-number resolution (PNR) based on accurate measurements of the detector’s response time to few-photon optical pulses. In this work, we investigate the impact of the optical pulse shape and duration on the accuracy of this method. We find that Gaussian temporal pulse shapes yield cleaner arrival-time histograms and, thus, more accurate PNR, compared to bandpass-filtered pulses of equal bandwidth. For low system jitter and an optical pulse duration comparable to the other jitter contributions, photon numbers can be discriminated in our system with a commercial SNSPD. At 60 ps optical pulse duration, photon-number discrimination is significantly reduced. Furthermore, we highlight the importance of using the correct arrival-time histogram model when analyzing photon-number assignment. Using exponentially modified Gaussian distributions, instead of the commonly used Gaussian distributions, we can more accurately determine photon-number misidentification probabilities. Finally, we reconstruct the positive operator-valued measures of the detector, revealing sharp features that indicate the intrinsic PNR capabilities.}},
author = {{Schapeler, Timon and Mischke, Isabell and Schlue, Fabian and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine and Bartley, Tim}},
issn = {{2835-0103}},
journal = {{APL Quantum}},
number = {{1}},
publisher = {{AIP Publishing}},
title = {{{Practical considerations for assignment of photon numbers with SNSPDs}}},
doi = {{10.1063/5.0304127}},
volume = {{3}},
year = {{2026}},
}
@inproceedings{60587,
author = {{Schapeler, Timon and Schlue, Fabian and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine and Bartley, Tim}},
booktitle = {{Advanced Photon Counting Techniques XIX}},
editor = {{Itzler, Mark A. and McIntosh, K. Alex and Bienfang, Joshua C.}},
publisher = {{SPIE}},
title = {{{Optimizing photon-number resolution with superconducting nanowire multi-photon detectors}}},
doi = {{10.1117/12.3054905}},
year = {{2025}},
}
@article{61110,
abstract = {{By analyzing the physics of multi-photon absorption in superconducting nanowire single-photon detectors (SNSPDs), we identify physical components of jitter. From this, we formulate a quantitative physical model of the multi-photon detector response that combines the local detection mechanism and local fluctuations (hotspot formation and intrinsic jitter) with the thermoelectric dynamics of resistive domains. Our model provides an excellent description of the arrival-time histogram of a commercial SNSPD across several orders of magnitude, both in arrival-time probability and across mean photon number. This is achieved with just three fitting parameters: the scaling of the mean arrival time of voltage response pulses, as well as the Gaussian and exponential jitter components. Our findings have important implications for photon-number-resolving detector design, as well as applications requiring low jitter, such as light detection and ranging (LIDAR).}},
author = {{Sidorova, Mariia and Schapeler, Timon and Semenov, Alexej D. and Schlue, Fabian and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine and Bartley, Tim}},
issn = {{2378-0967}},
journal = {{APL Photonics}},
keywords = {{Jitter, PNR, SNSPD}},
number = {{8}},
publisher = {{AIP Publishing}},
title = {{{Jitter in photon-number-resolved detection by superconducting nanowires}}},
doi = {{10.1063/5.0273752}},
volume = {{10}},
year = {{2025}},
}
@article{62911,
abstract = {{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.}},
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{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{54544,
abstract = {{The biphoton correlation time, a measure for the conditional uncertainty in the temporal arrival of two photons from a photon pair source, is a key performance identifier for many quantum spectroscopy applications, with shorter correlation times typically yielding better performance. Furthermore, it provides fundamental insight into the effects of dispersion on the biphoton state. Here, we show that a characteristic dependence of the width of the temporal interferogram can be exploited to obtain insights into the amount of second-order dispersion inside the interferometer and to retrieve actual and Fourier-limited ultrashort biphoton correlation times of around 100 fs. In the presented scheme, we simultaneously measure spectral and temporal interferograms at the output of an SU(1,1) interferometer based on an integrated broadband parametric down conversion source in a Ti:LiNbO3 waveguide.}},
author = {{Roeder, Franz and Pollmann, René and Stefszky, Michael and Santandrea, Matteo and Luo, Kai Hong and Quiring, V. and Ricken, Raimund and Eigner, Christof and Brecht, Benjamin and Silberhorn, Christine}},
issn = {{2691-3399}},
journal = {{PRX Quantum}},
number = {{2}},
publisher = {{American Physical Society (APS)}},
title = {{{Measurement of Ultrashort Biphoton Correlation Times with an Integrated Two-Color Broadband SU(1,1)-Interferometer}}},
doi = {{10.1103/prxquantum.5.020350}},
volume = {{5}},
year = {{2024}},
}
@article{55174,
abstract = {{We apply principal component analysis (PCA) to a set of electrical output signals from a commercially available superconducting nanowire single-photon detector (SNSPD) to investigate their photon-number-resolving capability. We find that the rising edge as well as the amplitude of the electrical signal have the most dependence on photon number. Accurately measuring the rising edge while simultaneously measuring the voltage of the pulse amplitude maximizes the photon-number resolution of SNSPDs. Using an optimal basis of principal components, we show unambiguous discrimination between one- and two-photon events, as well as partial resolution up to five photons. This expands the use case of SNSPDs to photon-counting experiments, without the need of detector multiplexing architectures.
Published by the American Physical Society
2024
}},
author = {{Schapeler, Timon and Lamberty, Niklas and Hummel, Thomas and Schlue, Fabian and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine and Bartley, Tim}},
issn = {{2331-7019}},
journal = {{Physical Review Applied}},
number = {{1}},
publisher = {{American Physical Society (APS)}},
title = {{{Electrical trace analysis of superconducting nanowire photon-number-resolving detectors}}},
doi = {{10.1103/physrevapplied.22.014024}},
volume = {{22}},
year = {{2024}},
}
@article{57743,
author = {{Krishnaswamy, Suchitra and Schlue, Fabian and Ares, L. and Dyachuk, V. and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine and Sperling, Jan}},
issn = {{2469-9926}},
journal = {{Physical Review A}},
number = {{2}},
publisher = {{American Physical Society (APS)}},
title = {{{Experimental retrieval of photon statistics from click detection}}},
doi = {{10.1103/physreva.110.023717}},
volume = {{110}},
year = {{2024}},
}
@article{63218,
abstract = {{Linear optical quantum networks, consisting of a quantum input state and a multiport interferometer, are an important building block for many quantum technological concepts, e.g., Gaussian boson sampling. Here, we propose the implementation of such networks based on frequency conversion by utilizing a so-called multioutput quantum pulse gate (MQPG). This approach allows the resource-efficient and therefore scalable implementation of frequency-bin-based, fully programmable interferometers in a single spatial and polarization mode. Quantum input states for this network can be provided by utilizing the strong frequency entanglement of a type-0 parametric down-conversion (PDC) source. Here, we develop a theoretical framework to describe linear networks based on an MQPG and PDC and utilize it to investigate the limits and scalabilty of our approach.
Published by the American Physical Society
2024
}},
author = {{Folge, Patrick Fabian and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine}},
issn = {{2691-3399}},
journal = {{PRX Quantum}},
number = {{4}},
publisher = {{American Physical Society (APS)}},
title = {{{A Framework for Fully Programmable Frequency-Encoded Quantum Networks Harnessing Multioutput Quantum Pulse Gates}}},
doi = {{10.1103/prxquantum.5.040329}},
volume = {{5}},
year = {{2024}},
}
@article{57862,
abstract = {{The latest applications in ultrafast quantum metrology require bright, broadband bi-photon sources with one of the photons in the mid-infrared and the other in the visible to near infrared. However, existing sources based on bulk crystals are limited in brightness due to the short interaction length and only allow for limited dispersion engineering. Here, we present an integrated PDC source based on a Ti:LiNbO3 waveguide that generates broadband bi-photons with central wavelengths at 860 nm and 2800 nm. Their spectral bandwidth exceeds 25 THz and is achieved by simultaneous matching of the group velocities (GVs) and cancellation of GV dispersion for the signal and idler field. We provide an intuitive understanding of the process by studying our source’s behavior at different temperatures and pump wavelengths, which agrees well with simulations.}},
author = {{Roeder, Franz and Gnanavel, Abira and Pollmann, René and Brecht, Olga and Stefszky, Michael and Padberg, Laura and Eigner, Christof and Silberhorn, Christine and Brecht, Benjamin}},
issn = {{1367-2630}},
journal = {{New Journal of Physics}},
number = {{12}},
publisher = {{IOP Publishing}},
title = {{{Ultra-broadband non-degenerate guided-wave bi-photon source in the near and mid-infrared}}},
doi = {{10.1088/1367-2630/ad9f98}},
volume = {{26}},
year = {{2024}},
}
@article{45485,
author = {{Kruse, Stephan and Serino, Laura and Folge, Patrick Fabian and Echeverria Oviedo, Dana and Bhattacharjee, Abhinandan and Stefszky, Michael and Scheytt, J. Christoph and Brecht, Benjamin and Silberhorn, Christine}},
issn = {{1041-1135}},
journal = {{IEEE Photonics Technology Letters}},
keywords = {{Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}},
number = {{14}},
pages = {{769--772}},
publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}},
title = {{{A Pulsed Lidar System With Ultimate Quantum Range Accuracy}}},
doi = {{10.1109/lpt.2023.3277515}},
volume = {{35}},
year = {{2023}},
}
@article{45850,
abstract = {{Interference between single photons is key for many quantum optics experiments and applications in quantum technologies, such as quantum communication or computation. It is advantageous to operate the systems at telecommunication wavelengths and to integrate the setups for these applications in order to improve stability, compactness and scalability. A new promising material platform for integrated quantum optics is lithium niobate on insulator (LNOI). Here, we realise Hong-Ou-Mandel (HOM) interference between telecom photons from an engineered parametric down-conversion source in an LNOI directional coupler. The coupler has been designed and fabricated in house and provides close to perfect balanced beam splitting. We obtain a raw HOM visibility of (93.5 ± 0.7) %, limited mainly by the source performance and in good agreement with off-chip measurements. This lays the foundation for more sophisticated quantum experiments in LNOI.}},
author = {{Babel, Silia and Bollmers, Laura and Massaro, Marcello and Luo, Kai Hong and Stefszky, Michael and Pegoraro, Federico and Held, Philip and Herrmann, Harald and Eigner, Christof and Brecht, Benjamin and Padberg, Laura and Silberhorn, Christine}},
issn = {{1094-4087}},
journal = {{Optics Express}},
keywords = {{Atomic and Molecular Physics, and Optics}},
number = {{14}},
publisher = {{Optica Publishing Group}},
title = {{{Demonstration of Hong-Ou-Mandel interference in an LNOI directional coupler}}},
doi = {{10.1364/oe.484126}},
volume = {{31}},
year = {{2023}},
}
@article{46138,
abstract = {{This work reports a fully guided setup for single-mode squeezing on integrated titanium-indiffused periodically poled nonlinear resonators. A continuous-wave laser beam is delivered and the squeezed field is collected by single-mode fibers; up to −3.17(9) dB of useful squeezing is available in fibers. To showcase the usefulness of such a fiber-coupled device, we applied the generated squeezed light in a fiber-based phase sensing experiment, showing a quantum enhancement in the signal-to-noise ratio of 0.35 dB. Moreover, our investigation of the effect of photorefraction on the cavity resonance condition suggests that it causes system instabilities at high powers.}},
author = {{Domeneguetti, Renato and Stefszky, Michael and Herrmann, Harald and Silberhorn, Christine and Andersen, Ulrik L. and Neergaard-Nielsen, Jonas S. and Gehring, Tobias}},
issn = {{0146-9592}},
journal = {{Optics Letters}},
keywords = {{Atomic and Molecular Physics, and Optics}},
number = {{11}},
publisher = {{Optica Publishing Group}},
title = {{{Fully guided and phase locked Ti:PPLN waveguide squeezing for applications in quantum sensing}}},
doi = {{10.1364/ol.486654}},
volume = {{48}},
year = {{2023}},
}
@article{44081,
author = {{Serino, Laura and Gil López, Jano and Stefszky, Michael and Ricken, Raimund and Eigner, Christof and Brecht, Benjamin and Silberhorn, Christine}},
issn = {{2691-3399}},
journal = {{PRX Quantum}},
keywords = {{General Physics and Astronomy, Mathematical Physics, Applied Mathematics, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, General Computer Science}},
number = {{2}},
publisher = {{American Physical Society (APS)}},
title = {{{Realization of a Multi-Output Quantum Pulse Gate for Decoding High-Dimensional Temporal Modes of Single-Photon States}}},
doi = {{10.1103/prxquantum.4.020306}},
volume = {{4}},
year = {{2023}},
}
@article{26889,
author = {{Luo, Kai Hong and Santandrea, Matteo and Stefszky, Michael and Sperling, Jan and Massaro, Marcello and Ferreri, Alessandro and Sharapova, Polina and Herrmann, Harald and Silberhorn, Christine}},
issn = {{2469-9926}},
journal = {{Physical Review A}},
title = {{{Quantum optical coherence: From linear to nonlinear interferometers}}},
doi = {{10.1103/physreva.104.043707}},
year = {{2021}},
}
@article{26077,
abstract = {{Nonlinear SU(1,1) interferometers are fruitful and promising tools for spectral engineering and precise measurements with phase sensitivity below the classical bound. Such interferometers have been successfully realized in bulk and fiber-based configurations. However, rapidly developing integrated technologies provide higher efficiencies, smaller footprints, and pave the way to quantum-enhanced on-chip interferometry. In this work, we theoretically realised an integrated architecture of the multimode SU(1,1) interferometer which can be applied to various integrated platforms. The presented interferometer includes a polarization converter between two photon sources and utilizes a continuous-wave (CW) pump. Based on the potassium titanyl phosphate (KTP) platform, we show that this configuration results in almost perfect destructive interference at the output and supersensitivity regions below the classical limit. In addition, we discuss the fundamental difference between single-mode and highly multimode SU(1,1) interferometers in the properties of phase sensitivity and its limits. Finally, we explore how to improve the phase sensitivity by filtering the output radiation and using different seeding states in different modes with various detection strategies.}},
author = {{Ferreri, Alessandro and Santandrea, Matteo and Stefszky, Michael and Luo, Kai Hong and Herrmann, Harald and Silberhorn, Christine and Sharapova, Polina R.}},
issn = {{2521-327X}},
journal = {{Quantum}},
title = {{{Spectrally multimode integrated SU(1,1) interferometer}}},
doi = {{10.22331/q-2021-05-27-461}},
year = {{2021}},
}
@inproceedings{39027,
abstract = {{We experimentally investigate the generation of continuous-wave optical squeezing from a titanium-indiffused lithium niobate waveguide resonator at low and high frequencies. The device promises integration with different platform chips for more complex optical systems.}},
author = {{Domeneguetti, Renato R. and Conradi, Hauke and Kleinert, Moritz and Kießler, Christian and Stefszky, Michael and Herrmann, Harald and Silberhorn, Christine and Andersen, Ulrik L. and Neergaard-Nielsen, Jonas Schou and Gehring, Tobias}},
booktitle = {{2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference}},
keywords = {{Optical systems, Polymer waveguides, Quantum key distribution, Quantum light sources, Squeezed states, Waveguides}},
pages = {{eb_4_1}},
publisher = {{Optica Publishing Group}},
title = {{{Nonlinear waveguides for integrated quantum light source}}},
year = {{2021}},
}
@article{26218,
author = {{Santandrea, Matteo and Stefszky, Michael and Silberhorn, Christine}},
issn = {{2040-8978}},
journal = {{Journal of Optics}},
title = {{{General analytic theory of classical collinear three-wave mixing in a monolithic cavity}}},
doi = {{10.1088/2040-8986/ac0b90}},
year = {{2021}},
}
@inproceedings{40374,
abstract = {{We present a frequency multimode integrated SU (1,1) interferometer with a polarization converter and strong signal-idler photon correlations. Phase sensitivity below the shot noise limit is demonstrated, various filtering and seeding strategies are discussed.}},
author = {{Ferreri, A. and Santandrea, Matteo and Stefszky, Michael and Luo, Kai Hong and Herrmann, Harald and Silberhorn, Christine and Sharapova, Polina}},
booktitle = {{Conference on Lasers and Electro-Optics}},
publisher = {{Optica Publishing Group}},
title = {{{Multimode integrated SU(1,1) interferometer}}},
doi = {{10.1364/cleo_qels.2021.ftu1n.6}},
year = {{2021}},
}
@article{22771,
author = {{Stefszky, Michael and Santandrea, Matteo and vom Bruch, Felix and Krapick, S. and Eigner, Christof and Ricken, R. and Quiring, V. and Herrmann, Harald and Silberhorn, Christine}},
issn = {{1094-4087}},
journal = {{Optics Express}},
title = {{{Waveguide resonator with an integrated phase modulator for second harmonic generation}}},
doi = {{10.1364/oe.412824}},
year = {{2020}},
}