Superconducting nanowire single-photon detectors (SNSPDs) are becoming increasingly popular for applications in quantum information and long-distance communication. While the detection efficiency of SNSPDs has significantly improved over time, their timing performance has largely remained unchanged. Furthermore, the photodetection process in superconducting nanowires is still not fully understood and subject to ongoing research. In this thesis, I will present a systematic study of the timing performance of different types of nanowire single-photon detectors. I will analyze the photodetection delay histogram (also called instrument response function IRF) of these detectors as a function of bias current, nanowire width and wavelength. The study of the IRF yielded several unexpected results, among them a wavelength-dependent exponential tail of the IRF and a discrepancy between experimental photodetection delay results and the predicted value based on the electrothermal model. These results reveal some shortcomings of the basic models used for SNSPDs, and may include a signature of the initial process by which photons are detected in superconducting nanowires. I will conclude this thesis by presenting a brief introduction into vortices, which have recently become a popular starting point for photodetection models for SNSPDs. Building on prior work, I will show that a simple image method can be used to calculate the current flow in presence of a vortex, and discuss possible implications of recent vortex-based models for timing jitter.
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Timing performance of superconducting nanowire single-photon detectors
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