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arXiv:2407.10231

Coincidence detection for photon triplet sources

Zijun Chen, Yeshaiahu Fainman

Published Jul 14, 2024• 0 citations
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Abstract

Photon triplet generation based on third-order spontaneous parametric down-conversion remains as an experimental challenge. The challenge stems from the trade-offs between source brightness and instrument noise. This work presents a probability theory of coincidence detection to address the detection limit in source characterization. We use Bayes' theorem to model instruments as a noisy communication channel and apply statistical inference to identify the minimum detectable coincidence rate. A triplet generation rate of 1-100 Hz is required for source characterization performed over 1-72 hours using superconducting nanowire single-photon detectors.

DOI
10.48550/arxiv.2407.10231

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Photon triplet generation based on third-order spontaneous parametric down-conversion remains as an experimental challenge. The challenge stems from the trade-offs between source brightness and instrument noise. This work presents a probability theory of coincidence detection to address the detection limit in source characterization. We use Bayes' theorem to model instruments as a noisy communication channel and apply statistical inference to identify the minimum detectable coincidence rate. A triplet generation rate of 1-100 Hz is required for source characterization performed over 1-72 hours using superconducting nanowire single-photon detectors.
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We analyze the generation rates and preparation fidelities of photon triplet states in pulsed cascaded parametric down-conversion (PDC) under realistic experimental circumstances. As a model system, we assume a monolithically integrated device with negligible interface loss between the two consecutive PDC stages. We model the secondary down-conversion process in terms of a lossy channel and provide a detailed analysis of noise contributions. Taking variable pump powers into account, we estimate the impact of higher-order photon contributions and conversion processes on the achievable coincidence probabilities. At mean photon numbers of ⟨m⟩∼0.25\langle m\rangle\sim0.25⟨m⟩∼0.25 photons per pulse behind the first PDC stage, we expect around 4.04.04.0 genuine photon triplets per hour. Additionally, we discuss fundamental limitations of our model system as well as feasible improvements to the detectable photon triplet rate.
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.
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