@article{63451,
  abstract     = {{<jats:p>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.</jats:p>}},
  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     = {{<jats:p>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).</jats:p>}},
  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{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     = {{<jats:p>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.</jats:p>
          <jats:sec>
            <jats:title/>
            <jats:supplementary-material>
              <jats:permissions>
                <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement>
                <jats:copyright-year>2024</jats:copyright-year>
              </jats:permissions>
            </jats:supplementary-material>
          </jats:sec>}},
  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{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     = {{<jats:p>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.</jats:p>}},
  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{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{33670,
  author       = {{Schapeler, Timon and Bartley, Tim}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  number       = {{1}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Information extraction in photon-counting experiments}}},
  doi          = {{10.1103/physreva.106.013701}},
  volume       = {{106}},
  year         = {{2022}},
}

@article{23727,
  author       = {{Schapeler, Timon and Höpker, Jan Philipp and Bartley, Tim}},
  issn         = {{0953-2048}},
  journal      = {{Superconductor Science and Technology}},
  title        = {{{Quantum detector tomography of a high dynamic-range superconducting nanowire single-photon detector}}},
  doi          = {{10.1088/1361-6668/abee9a}},
  year         = {{2021}},
}

@article{37933,
  abstract     = {{<jats:p>We present a time-over-threshold readout technique to count the number of activated pixels from an array of superconducting nanowire single photon detectors (SNSPDs). This technique places no additional heatload on the cryostat, and retains the intrinsic count rate of the time-tagger. We demonstrate proof-of-principle operation with respect to a four-pixel device. Furthermore, we show that, given some permissible error threshold, the number of pixels that can be reliably read out scales linearly with the intrinsic signal-to-noise ratio of the individual pixel response.</jats:p>}},
  author       = {{Tiedau, Johannes and Schapeler, Timon and Anant, Vikas and Fedder, Helmut and Silberhorn, Christine and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{Atomic and Molecular Physics, and Optics}},
  number       = {{4}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Single-channel electronic readout of a multipixel superconducting nanowire single photon detector}}},
  doi          = {{10.1364/oe.383111}},
  volume       = {{28}},
  year         = {{2020}},
}

@article{20156,
  author       = {{Schapeler, Timon and Höpker, Jan Philipp and Bartley, Tim}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  title        = {{{Quantum detector tomography of a 2×2 multi-pixel array of superconducting nanowire single photon detectors}}},
  doi          = {{10.1364/oe.404285}},
  year         = {{2020}},
}