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Conclusion

Conclusion & outlook

The original research paper on time walk analysis 1 included comments on the potential for time walk correction in situations where the reset reset time of the nanowire is considerably shorter than the reset dynamics of the amplifier chain:

To optimally correct for this, higher-order correction techniques are needed based on higher-dimensional lookup tables. There is an avenue for exploring such methods for unique use-cases. 1

This potential for higher order correction methods turned out to be fruitful, which is why the prior section about higher corder correction adapted from the PEACOQ paper 2 is included. The original paper went on to claim that there are avenues for exploring time walk correction for pulses measured at multiple voltage levels, or even fully digitized pulses captured with high speed ADCs and FPGAs. These more rigorous readout techniques may be needed to deconvolve photon timing and Photon Number Resolution (PNR) effects from the same nanowire at high count rates 3. While drafting this thesis, methods for simultaneous time walk correction and PNR correction have not been demonstrated in the literature. However, I believe there is imminent potential to extend the Gaussian mixture model methods introduced in the next section for these purposes.

There are other types of extensions and modifications to the presented time walk correction method that may prove to be useful. However, the single-\(\Delta t\) measurement approach primarily detailed in this chapter is broadly applicable and straightforward to implement. For insight into developing a streamlined calibration process and in-situ time walk correction as part of larger quantum communication experiments, see the time walk correction section in the chapter 4 .

As applications like LIDAR and quantum communication demand ever higher data rates, multiple techniques for increasing photon and data throughput of SNSPD systems are being explored. Arrays or multi-channel SNSPD systems will play a role in satisfying that demand. However, compared to multiple lower count rate SNSPDs operating in parallel, a single detector operating at high rate has certain advantages. First, it makes more efficient use of the extensive bandwidth of the RF readout channel. Second, the single detector with single readout line puts less thermal load on the cooling system than multiple detectors with multiple readout lines. Therefore, paths toward operating individual SNSPDs at the limits of their count rate performance should be explored before extending to multi-pixel systems. This work is a step towards unlocking all available performance and timing precision of SNSPDs operated at high count rates.

  1. Mueller, A., Wollman, E. E., Korzh, B., Beyer, A. D., Narvaez, L., Rogalin, R., Spiropulu, M., et al. (2023). <b>Time-walk and jitter correction in SNSPDs at high count rates</b>. <i>Applied Physics Letters</i>, <i>122</i>(4). doi:10.1063/5.0129147 ↩↩

  2. Craiciu, I., Korzh, B., Beyer, A. D., Mueller, A., Allmaras, J. P., Narváez, L., Spiropulu, M., et al. (2023). <b>High-speed detection of 1550 & #x2009; & #x2009;nm single photons with superconducting nanowire detectors</b>. <i>Optica</i>, <i>10</i>(2), 183–190. doi:10.1364/OPTICA.478960 ↩

  3. Hao, H., Zhao, Q.-Y., Kong, L.-D., Chen, S., Wang, H., Huang, Y.-H., Guo, J.-W., et al. (2021). <b>Improved pulse discrimination for a superconducting series nanowire detector by applying a digital matched filter</b>. <i>Applied Physics Letters</i>, <i>119</i>(23), 232601. doi:10.1063/5.0068449 ↩