Daniele Vogrig

For quantum communication applications, time-to-digital converters (TDCs) are a crucial tool whose performance can severely affect the quality of the entire application. Nowadays, FPGA-based TDCs present a viable alternative to ASIC ones, once the nonlinear behaviour due to the intrinsic nature of the device is properly mitigated. To compensate said nonlinearities, a calibration procedure is required. Maintaining this calibration consistent during long measurements requires either interpolation methods or stopping data acquisition for a fixed time to perform the calibration process. Here we present a design and demonstration of an FPGA-based TDC showing a residual jitter of 27 ps, that is scalable for multichannel operation. We present a unique calibration method that exploits single-photon detection, which does not require stopping the data acquisition or using any interpolation methods, while keeping the device calibrated to the best of its ability. This allows Bob to receive time-tags with the best possible accuracy while also removing data-loss phases. This calibration method was tested in a relevant environment, investigating the device behaviour between 5 °C and 80 °C, where the residual jitter of the TDC was shown to be kept under control.