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IEEE photonics journal

A Precise High Count-Rate FPGA Based Multi-Channel Coincidence Counting System for Quantum Photonics Applications

E. Arabul, Stefano Paesani, Scott Tancock, John Rarity, Naim Dahnoun

Published Jan 22, 2020• 17 citations

Abstract

Coincidence counters play the role of gating events from the background noise in almost every quantum photonics setup. Precise multi-channel and high count-rate coincidence counting tools have become desirable due to an increase in the complexity of quantum photonics experiments. However, timing analyzers are struggling to meet these needs. We are proposing a Field Programmable Gate Array (FPGA) based coincidence counting system which provides 8 operational channels with 8.9 ps root mean square (RMS) resolution (with a bin width of 7.7 ps) and a count-rate of 320 million counts per second (MCPS) (with 40 MCPS per channel). We have successfully tested our design in different quantum photonics scenarios such as the detection of two-photon interference and pseudo-photon-number resolving detection of a coherent state of light where it has shown its capability of working beyond the saturation of detectors. Also, we have introduced a Dual Data Rate Registration TDC, which improved the linearity of the time tagging operation by using both clock edges without increasing the dead-time or using the space excessively. 1.2 LSB in max DNL error, 1.8 LSB in max INL error, 10 ps in FWHM and 3.2 ps in RMS resolution improvements were achieved.

DOI: 10.1109/jphot.2020.2968724

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Real-time analysis of single-photon coincidence is critical in photonic quantum computing. The large channel number and high counting rate foreseen in such experiments pose a big challenge for the conventional time tagged method and coincidence instruments. Here we propose a real-time time-tagged coincidence method and a data filtering solution, demonstrated by a 32-channel coincidence counting unit that has been implemented successfully on a field-programmable gate array system. The unit provides high counting rates, a tunable coincidence window, and a timing resolution of 390 ps. Beyond that, it is feasible to be scaled up to 104 channels and is thus ideally suited for channel consuming applications such as boson sampling. Based on the versatility and scalability the unit has shown, we believe that it is the turn-key solution for many single-photon coincidence counting applications in photonic quantum computing.

Coincidence counting is widely used in quantum optics.It could be used in measuring the pairs of polarization entangled photons and single photon interference.In quantum experiments,coincidence counting often needs more than 3 channels.In this case,it is necessary to use FPGA(Field-Programmable Gate Array) instead of discrete logic chips.FPGA also has the advantage of low cost and small size.Coincidence counter based on FPGA could support coincidence time window from 1 ns to several hundred ns.This helps to avoid noised caused by background light.This paper introduces the principle of multi-channel coincidence counter based on FPGA and gives its performance experimentally with two single photon counting modules.

The increasing complexity of recent photonic experiments challenges the development of efficient multichannel coincidence counting systems with high-level functionality. Here, we report a coincidence unit able to count detection events ranging from single to 16-fold coincidences with full channel-number resolution. The device operates within sub-100-ps coincidence time windows, with a maximum input frequency of 1.5 GHz and an overall jitter of less than 10 ps. The unit high-level timing performance renders it suitable for quantum photonic experiments employing low-timing-jitter single-photon detectors. Additionally, the unit can be used in complex photonic systems to drive feed-forward loops. We demonstrate the developed coincidence counting unit in photon-number-resolving detection to directly quantify the statistical properties of light, specifically coherent and thermal states, with a fidelity exceeding 0.999 up to 60 photons.

The high-rate detection of entangled photons is essential for advancing photonic quantum information processing. Although several experimental demonstrations have been reported, the achievable coincidence rates have so far remained limited. One of the main bottlenecks arises from the dead time of single-photon detectors, which constrains coincidence detection at high photon-pair generation rates. In this work, we employ 16-pixel superconducting nanowire single-photon detectors (SNSPDs) to mitigate the impact of detector dead time. Consequently, we achieve coincidence rates exceeding 3 million counts per second (Mcps) in two-photon interference and CHSH inequality experiments using a 5-GHz clocked sequential time-bin entangled photon pair source. To the best of our knowledge, this is the first demonstration of multi-Mcps coincidence detection of entangled photons, paving the way for high-speed entangled-photon-based quantum information processing.

In the field of quantum optics, especially in various experiments involving characterizing entangled photon pairs or quantum correlation effects, coincidence systems are primarily employed to detect and record temporal correlations between multiple photon events. Certain experiments propose higher requirements for the time precision of coincidence electronics, aiming to achieve high-precision time measurements with single-channel time resolution of ~10 ps RMS. To support diverse quantum optics experiments, a 32-channel high-precision coincidence module has been designed and fabricated. A series of tests have been conducted, and the results show that the time precision of each channel of the electronics is better than 10 ps RMS. Furthermore, preliminary experimental applications in quantum optics experiments have been successfully conducted.

We present results characterizing multichannel InGaAs single photon detectors utilizing gated passive quenching circuits (GPQC), self-differencing techniques, and field programmable gate array (FPGA)-based logic for both diode gating and coincidence counting. Utilizing FPGAs for the diode gating frontend and the logic counting backend has the advantage of low cost compared to custom built logic circuits and current off-the-shelf detector technology. Further, FPGA logic counters have been shown to work well in quantum key distribution (QKD) test beds. Our setup combines multiple independent detector channels in a reconfigurable manner via an FPGA backend and post processing in order to perform coincidence measurements between any two or more detector channels simultaneously. Using this method, states from a multi-photon polarization entangled source are detected and characterized via coincidence counting on the FPGA. Photons detection events are also processed by the quantum information toolkit for application testing (QITKAT).