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International Conference on Electronics, Integrated Circuits and Communication Technology (EICCT)

Design and Testing of Coincidence Module for Quantum Optical Research

Haoqian Xu, D. J. Li, Yuxuan Chen, Haoshu Tian, Jiajun Qin, Hao Han, Zhe Cao, Jiaming Li, Kairen Chen, Lei Zhao

Published Jul 11, 2025• 0 citations
Publisher

Abstract

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.

DOI
10.1109/eicct65471.2025.11100074

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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.
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.
Precise time measurement and event correlation have gained a prominent role in a large variety of quantum photonics applications, including quantum communication, quantum simulation, and quantum computing. The increasing complexity and scale of quantum photonic systems, particularly those capable of generating, manipulating, and detecting single photons, necessitate advanced electronic timing systems that can accurately capture coincidence events across multiple channels. A highly effective approach for measuring the time of arrival of a photon, detected by single-photon detectors such as single-photon avalanche diodes (SPADs) or superconducting nanowires, is the cascading of a time-to-amplitude converter (TAC) with an analog-to-digital converter (ADC), a configuration distinguished by its high precision and linearity [1].
Precisely timed detection of single photons plays an important role in the field of quantum information processing and fluorescence sensing. The method of time-correlated single photon counting is therefore constantly evolving and the associated instrumentation is being improved with new ideas and technologies. Simultaneous, time tagged readout of multiple detector channels is invaluable in many applications, spanning from fluorescence lifetime imaging in biology to the measurement of quantum optical correlations in basic research. Here we present a new integrated design, providing up to three independent input channels, a very short dead time, very high throughput, and a timing resolution of 25 ps at reasonable cost and small size. Apart from design features and test results of the instrument, we show an application in quantum optics, namely, the measurement of the photon statistics of a heralded single photon source based on cavity-enhanced spontaneous parametric down-conversion.
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.
High-precision nonlocal temporal correlation identification in entangled photon pairs is critical to measure the time offset between remote independent time scales for many quantum information applications. The first nonlocal correlation identification was reported in 2009, which extracts the time offset via the algorithm of iterative fast Fourier transformations and their inverse. The best identification resolution is restricted by the peak identification threshold of the algorithm, and thus the time offset calculation precision is limited. In this paper, an improvement for the identification is presented both in resolution and precision via a modified algorithm of direct cross correlation extraction. A flexible resolution down to 1 ps is realized, which is only dependent on the least significant bit resolution of the time-tagging device. The attainable precision is shown to be mainly determined by the inherent timing jitter of single photon detectors, the acquired pair rate, and acquisition time, and a sub-picosecond precision (0.72 ps) has been achieved at an acquisition time of 4.5 s. This high-precision nonlocal measurement realization provides a solid foundation for the field applications of entanglement-based quantum clock synchronization, ranging, and communications.
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.