A Precise High Count-Rate Multi-Channel Coincidence Counting Instrument for Quantum Photonics Applications

Abstract

Coincidence counters play the role of gating the correlated events from the background noise in almost every quantum photonics setup. To provide flexibility and precision in experiments, commonly Time-to-Digital Converters (TDCs) are utilised for implementing coincidence counters. TDCs are instruments used for converting time events into digital numbers, and typically in quantum photonics experiments, they are used for the time-stamping of photons’ arrival times. With recent developments in quantum photonics, precise multi-channel and high count-rate coincidence counting tools have become desirable due to the increase in the complexity of quantum photonics experiments. However, timing analyser instruments are struggling to meet with the performance requirements of these experiments and becoming limiting factors. In this research, Field Programming Gate Array (FPGA) based methods have been researched to integrate a precise multi-channel TDC with a coincidence counting instrument into the same FPGA fabric. To achieve this, a 512-bin carry chain based tapped delay line TDC has been developed in a Spartan6 LX150 FPGA. The developed TDC scheme (Dual Data-Rate Registration TDC) was unique in a way that it uses both clock edges to register the trigger and applying an averaging technique in combination with the code density calibration to improve the linearity. The advantages of this method were without changing the number of delay lines used or introducing an additionaldead-time,betterlinearitywasachieved.Byusingthismethod8.9psSingle Shot Precision (SSP) (with a bin width of 7.7 ps), 12.6 ps standard deviation, FullWidth-Half-Maximum (FWHM) of 29.6 ps, the max DNL error of 2.9 LSB and max INL of 8.8 LSB were achieved. This TDC scheme was used to implement a multi-channel labelling coincidence counting method. This method integrates the TDC and coincidence counter implementations into the same chip while using a multi-stop LiDAR approach to achieve optimum real-time operation. This system provided 8-channels with adjustable digital delaysandwindowsizesforeachchannel.Thecoincidencecountingoperationachieved 40 million counts per second (MCPS), and for 8 operational channel, the total of 320 MCPS was achieved. This result was the best-achieved count-rate for an 8 or more channel coincidence counting system with a sub-10 ps precision. Also, the smallest window size which could precisely capture all coincidences were observed as 107 ps, whilethesettablesmallestwindowwas7.7ps.Also,thesystemwassuccessfullytested in quantum photonics applications such as the rev-HOM dip measurement and the pseudo-photon-number resolving detection of a coherent state of light. The future work for this research involves improving the precision by adding multiple phases to the TDC registration scheme, improving the coincidence counting implementation for an additional number of channels and improving the count-rate of the system by developing a dual data-rate TDC.

Date of Award	29 Sept 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Naim Dahnoun (Supervisor) & John G Rarity (Supervisor)