@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}}, } @article{60136, abstract = {{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 in situ 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.}}, 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}}, } @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{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{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{55553, abstract = {{Cryogenic opto-electronic interconnects are gaining increasing interest as a means to control and readout cryogenic electronic components. The challenge is to achieve sufficient signal integrity with low heat load processing. In this context, we demonstrate the opto-electronic bias and readout of a commercial four-pixel superconducting nanowire single-photon detector array using a cryogenic photodiode and laser. We show that this approach has a similar system detection efficiency to a conventional bias. Furthermore, multi-pixel detection events are faithfully converted between the optical and electrical domains, which allows reliable extraction of amplitude multiplexed photon statistics. Our device has a latent heat load of 2.6 mW, maintains a signal rise time of 3 ns, and operates in free-running (self-resetting) mode at a repetition rate of 600 kHz. This demonstrates the potential of high-bandwidth, low noise, and low heat load opto-electronic interconnects for scalable cryogenic signal processing and transmission.}}, author = {{Thiele, Frederik and Lamberty, Niklas and Hummel, Thomas and Bartley, Tim}}, issn = {{2378-0967}}, journal = {{APL Photonics}}, number = {{7}}, publisher = {{AIP Publishing}}, title = {{{Optical bias and cryogenic laser readout of a multipixel superconducting nanowire single photon detector}}}, doi = {{10.1063/5.0209458}}, volume = {{9}}, year = {{2024}}, } @article{52876, author = {{Arends, Christian and Wolf, Lasse Lennart and Meinecke, Jasmin and Barkhofen, Sonja and Weich, Tobias and Bartley, Tim}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, keywords = {{General Physics and Astronomy}}, number = {{1}}, publisher = {{American Physical Society (APS)}}, title = {{{Decomposing large unitaries into multimode devices of arbitrary size}}}, doi = {{10.1103/physrevresearch.6.l012043}}, volume = {{6}}, year = {{2024}}, } @article{51356, abstract = {{Abstract 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 LiNbO3 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.}}, 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{53202, abstract = {{At large scales, quantum systems may become advantageous over their classical counterparts at performing certain tasks. Developing tools to analyze these systems at the relevant scales, in a manner consistent with quantum mechanics, is therefore critical to benchmarking performance and characterizing their operation. While classical computational approaches cannot perform like-for-like computations of quantum systems beyond a certain scale, classical high-performance computing (HPC) may nevertheless be useful for precisely these characterization and certification tasks. By developing open-source customized algorithms using high-performance computing, we perform quantum tomography on a megascale quantum photonic detector covering a Hilbert space of 106. This requires finding 108 elements of the matrix corresponding to the positive operator valued measure (POVM), the quantum description of the detector, and is achieved in minutes of computation time. Moreover, by exploiting the structure of the problem, we achieve highly efficient parallel scaling, paving the way for quantum objects up to a system size of 1012 elements to be reconstructed using this method. In general, this shows that a consistent quantum mechanical description of quantum phenomena is applicable at everyday scales. More concretely, this enables the reconstruction of large-scale quantum sources, processes and detectors used in computation and sampling tasks, which may be necessary to prove their nonclassical character or quantum computational advantage.}}, author = {{Schapeler, Timon and Schade, Robert and Lass, Michael and Plessl, Christian and Bartley, Tim}}, journal = {{Quantum Science and Technology}}, number = {{1}}, publisher = {{IOP Publishing}}, title = {{{Scalable quantum detector tomography by high-performance computing}}}, doi = {{10.1088/2058-9565/ad8511}}, volume = {{10}}, year = {{2024}}, } @article{50840, abstract = {{Superconducting nanowire single-photon detectors (SNSPDs) have been widely used to study the discrete nature of quantum states of light in the form of photon-counting experiments. We show that SNSPDs can also be used to study continuous variables of optical quantum states by performing homodyne detection at a bandwidth of 400 kHz. By measuring the interference of a continuous-wave field of a local oscillator with the field of the vacuum state using two SNSPDs, we show that the variance of the difference in count rates is linearly proportional to the photon flux of the local oscillator over almost five orders of magnitude. The resulting shot-noise clearance of (46.0 ± 1.1) dB is the highest reported clearance for a balanced optical homodyne detector, demonstrating their potential for measuring highly squeezed states in the continuous-wave regime. In addition, we measured a CMRR = 22.4 dB. From the joint click counting statistics, we also measure the phase-dependent quadrature of a weak coherent state to demonstrate our device’s functionality as a homodyne detector.}}, author = {{Protte, Maximilian and Schapeler, Timon and Sperling, Jan and Bartley, Tim}}, issn = {{2837-6714}}, journal = {{Optica Quantum}}, number = {{1}}, publisher = {{Optica Publishing Group}}, title = {{{Low-noise balanced homodyne detection with superconducting nanowire single-photon detectors}}}, doi = {{10.1364/opticaq.502201}}, volume = {{2}}, year = {{2024}}, } @article{48399, abstract = {{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.}}, 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{44044, abstract = {{Dispersion is present in every optical setup and is often an undesired effect, especially in nonlinear-optical experiments where ultrashort laser pulses are needed. Typically, bulky pulse compressors consisting of gratings or prisms are used to address this issue by precompensating the dispersion of the optical components. However, these devices are only able to compensate for a part of the dispersion (second-order dispersion). Here, we present a compact pulse-shaping device that uses plasmonic metasurfaces to apply an arbitrarily designed spectral phase delay allowing for a full dispersion control. Furthermore, with specific phase encodings, this device can be used to temporally reshape the incident laser pulses into more complex pulse forms such as a double pulse. We verify the performance of our device by using an SHG-FROG measurement setup together with a retrieval algorithm to extract the dispersion that our device applies to an incident laser pulse.}}, author = {{Geromel, René and Georgi, Philip and Protte, Maximilian and Lei, Shiwei and Bartley, Tim and Huang, Lingling and Zentgraf, Thomas}}, issn = {{1530-6984}}, journal = {{Nano Letters}}, keywords = {{Mechanical Engineering, Condensed Matter Physics, General Materials Science, General Chemistry, Bioengineering}}, number = {{8}}, pages = {{3196 -- 3201}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Compact Metasurface-Based Optical Pulse-Shaping Device}}}, doi = {{10.1021/acs.nanolett.2c04980}}, volume = {{23}}, year = {{2023}}, } @inproceedings{46485, abstract = {{We present a miniaturized pulse shaping device that creates an arbitrary dispersion through the interaction of multiple metasurfaces on less than 2 mm3 volume. For this, a metalens and a grating-metasurface between two silver mirrors are fabricated. The grating contains further phase information to achieve the device's pulse shaping functionality.}}, author = {{Geromel, René and Georgi, Philip and Protte, Maximilian and Bartley, Tim and Huang, Lingling and Zentgraf, Thomas}}, booktitle = {{CLEO: Fundamental Science 2023}}, location = {{San Jose, USA}}, publisher = {{Optica Publishing Group}}, title = {{{Dispersion control with integrated plasmonic metasurfaces}}}, doi = {{10.1364/cleo_fs.2023.fth4d.3}}, year = {{2023}}, } @article{36471, abstract = {{Superconducting nanowire single-photon detectors (SNSPDs) show near unity efficiency, low dark count rate, and short recovery time. Combining these characteristics with temporal control of SNSPDs broadens their applications as in active de-latching for higher dynamic range counting or temporal filtering for pump-probe spectroscopy or LiDAR. To that end, we demonstrate active gating of an SNSPD with a minimum off-to-on rise time of 2.4 ns and a total gate length of 5.0 ns. We show how the rise time depends on the inductance of the detector in combination with the control electronics. The gate window is demonstrated to be fully and freely, electrically tunable up to 500 ns at a repetition rate of 1.0 MHz, as well as ungated, free-running operation. Control electronics to generate the gating are mounted on the 2.3 K stage of a closed-cycle sorption cryostat, while the detector is operated on the cold stage at 0.8 K. We show that the efficiency and timing jitter of the detector is not altered during the on-time of the gating window. We exploit gated operation to demonstrate a method to increase in the photon counting dynamic range by a factor 11.2, as well as temporal filtering of a strong pump in an emulated pump-probe experiment.}}, author = {{Hummel, Thomas and Widhalm, Alex and Höpker, Jan Philipp and Jöns, Klaus and Chang, Jin and Fognini, Andreas and Steinhauer, Stephan and Zwiller, Val and Zrenner, Artur and Bartley, Tim}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{Atomic and Molecular Physics, and Optics}}, number = {{1}}, publisher = {{Optica Publishing Group}}, title = {{{Nanosecond gating of superconducting nanowire single-photon detectors using cryogenic bias circuitry}}}, doi = {{10.1364/oe.472058}}, volume = {{31}}, year = {{2023}}, } @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{26747, abstract = {{Metasurfaces provide applications for a variety of flat elements and devices due to the ability to modulate light with subwavelength structures. The working principle meanwhile gives rise to the crucial problem and challenge to protect the metasurface from dust or clean the unavoidable contaminants during daily usage. Here, taking advantage of the intelligent bioinspired surfaces which exhibit self-cleaning properties, a versatile dielectric metasurface benefiting from the obtained superhydrophilic or quasi-superhydrophobic states is shown. The design is realized by embedding the metasurface inside a large area of wettability supporting structures, which is highly efficient in fabrication, and achieves both optical and wettability functionality at the same time. The superhydrophilic state enables an enhanced optical response with water, while the quasi-superhydrophobic state imparts the fragile antennas an ability to self-clean dust contamination. Furthermore, the metasurface can be easily switched and repeated between these two wettability or functional states by appropriate treatments in a repeatable way, without degrading the optical performance. The proposed design strategy will bring new opportunities to smart metasurfaces with improved optical performance, versatility, and physical stability.}}, author = {{Lu, Jinlong and Sain, Basudeb and Georgi, Philip and Protte, Maximilian and Bartley, Tim and Zentgraf, Thomas}}, issn = {{2195-1071}}, journal = {{Advanced Optical Materials}}, number = {{1}}, publisher = {{Wiley}}, title = {{{A Versatile Metasurface Enabling Superwettability for Self‐Cleaning and Dynamic Color Response}}}, doi = {{10.1002/adom.202101781}}, volume = {{10}}, year = {{2022}}, } @article{33671, abstract = {{Abstract We demonstrate the fabrication of micron-wide tungsten silicide superconducting nanowire single-photon detectors on a silicon substrate using laser lithography. We show saturated internal detection efficiencies with wire widths ranging from 0.59 µm to 1.43 µm under illumination at 1550 nm. We demonstrate both straight wires, as well as meandered structures. Single-photon sensitivity is shown in devices up to 4 mm in length. Laser-lithographically written devices allow for fast and easy structuring of large areas while maintaining a saturated internal efficiency for wire widths around 1 µm.}}, author = {{Protte, Maximilian and Verma, Varun B and Höpker, Jan Philipp and Mirin, Richard P and Woo Nam, Sae and Bartley, Tim}}, issn = {{0953-2048}}, journal = {{Superconductor Science and Technology}}, keywords = {{Materials Chemistry, Electrical and Electronic Engineering, Metals and Alloys, Condensed Matter Physics, Ceramics and Composites}}, number = {{5}}, publisher = {{IOP Publishing}}, title = {{{Laser-lithographically written micron-wide superconducting nanowire single-photon detectors}}}, doi = {{10.1088/1361-6668/ac5338}}, volume = {{35}}, year = {{2022}}, } @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}}, }