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arXiv:2404.03236 · Laser & Photonics Review

Bright Heralded Single‐Photon Source Saturating Theoretical Single‐photon Purity

Haoyang Wang, Huihong Yuan, Qiang Zeng, Lai Zhou, Haiqiang Ma, Zhiliang L. Yuan

Published Feb 6, 2025• 12 citations
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Abstract

Abstract Single‐photon source is the cornerstone for modern quantum information processing. The present work derives the theoretical limit of single‐photon purity for general parametric heralded single‐photon sources , and subsequently demonstrates a bright, gigahertz‐pulsed heralded source with the purity saturating the limit. By stimulating spontaneous four‐wave mixing effect in the silicon spiral waveguide, this on‐chip source is measured to have a coincidence rate exceeding 1.5 MHz at a coincidence‐to‐accidental ratio (CAR) of 16.77 in the photon pair correlation experiment. The single‐photon purity of this source, quantified by the heralded auto‐correlation function , is measured by a heralded Hanbury Brown–Twiss setup to reach the theoretical limit with the lowest value of obtained at a coincidence rate of 0.8 kHz and a CAR of 2220. The performance improvements are attributed to effective spectral filtering suppressing the noise as well as the coherent pump condition helped by optical injection locking. The reported results provide a reliable standard for benchmarking heralded single‐photon sources and present a state‐of‐the‐art heralded source for quantum information processing.

DOI
10.1002/lpor.202401420

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Abstract Single‐photon source is the cornerstone for modern quantum information processing. The present work derives the theoretical limit of single‐photon purity for general parametric heralded single‐photon sources , and subsequently demonstrates a bright, gigahertz‐pulsed heralded source with the purity saturating the limit. By stimulating spontaneous four‐wave mixing effect in the silicon spiral waveguide, this on‐chip source is measured to have a coincidence rate exceeding 1.5 MHz at a coincidence‐to‐accidental ratio (CAR) of 16.77 in the photon pair correlation experiment. The single‐photon purity of this source, quantified by the heralded auto‐correlation function , is measured by a heralded Hanbury Brown–Twiss setup to reach the theoretical limit with the lowest value of obtained at a coincidence rate of 0.8 kHz and a CAR of 2220. The performance improvements are attributed to effective spectral filtering suppressing the noise as well as the coherent pump condition helped by optical injection locking. The reported results provide a reliable standard for benchmarking heralded single‐photon sources and present a state‐of‐the‐art heralded source for quantum information processing.
We derive the theoretical limit of single-photon purity of heralded single-photon sources and accordingly demonstrate a bright, gigahertz-pulsed heralded source with the purity saturating the limit. Based on spontaneous four-wave mixing in a silicon spiral waveguide, this on-chip source is measured to have a coincidence rate exceeding 1.5MHz at a coincidence to accidental (CAR) ratio of 16.77. The single-photon purity, quantified by the auto-correlation function gh(2)(0), reaches the theoretical limit with the lowest value of 0.00094 ± 0.00002 obtained at a coincidence rate of 0.8kHz. We attribute our results to effective spectral filtering as well as the coherent pump condition helped by optical injection locking.
On-chip heralded single photon sources are of key importance in the development of chip-scale devices exploiting the quantum properties of light. Single photon states can be produced as single photons heralded from correlated photon pairs generated through spontaneous four wave mixing. On-chip heralded single photon sources based on spontaneous four wave mixing have been already demonstrated. However, the heralded and herald photons are usually generated with wavelengths very close to the pump one, limiting the pump rejection efficiency and the application to the mid infrared. Moreover, the common sources of heralded photons based on spontaneous four wave mixing require spectral post filtering to achieve high purity, limiting the brightness and the integration of these sources. A solution to these problems can be provided by intermodal four wave mixing. In this work, we demonstrate the generation of photon pairs through intermodal four wave mixing in silicon waveguides, measuring the coincidences between the idler at 1.281 μm and the signal at 1.952 μm. We then discuss the application of intermodal four wave mixing to on-chip heralded single photon sources.
We investigate theoretically the spontaneous four-wave mixing (FWM) process that occurs in optical waveguides, as a source of quantum correlated photon-pairs. We consider that the waveguide used to implement the spontaneous FWM process presents a high value of nonlinear parameter, γ = 93.4 W-1m-1, and a non-negligible value of loss coefficient, α = 133.3 dB/m. Moreover, the theoretical model also consider the Raman scattering that inevitably accompanies the FWM process, and generates time-uncorrelated (noise) photon pairs. We use the coincident-to-accidental ratio (CAR) as a figure of merit of the photon pair source, and we were able to observe a CAR of the order of 65 in a high loss regime. After, we use the time-correlated photon pairs generated by the spontaneous FWM process to implement a heralded single photon source at waveguide output. In this scenario, the detection of one photon of the pair heralds the presence of the other photon. The quality of the source was studied by the evaluation of the second order coherence function for one photon of the pair conditioned by the detection of its twin photon. We observe that the presence of a high loss coefficient tends to improve the quality of the photon source, when compared with the lossless regime, even considering the Raman noise photons. We obtain a value for the conditional second order coherence function of the order of 0.11 in absence of loss, and a value of 0.03 for a loss coefficient of 133.3 dB/m.
We demonstrate a miniaturized, scalable high rate, pulsed single-photon source in the telecom band obtained by heralding a spontaneous parametric downconversion source pumped with a highly tunable GHz repetition rate pulsed laser in an all-guided wave scheme. For developing this source, we first perform second harmonic generation of ultrashort pump pulses varying with GHz rate at the telecom wavelength. Our investigation demonstrates a trade-off between the spectral brightness and the single-photon purity of the heralded single-photon source by controlling the repetition rate of pump pulses. For a 5 GHz repetition rate, a periodically poled lithium niobate waveguide in type-0 configuration produces the highest spectral brightness ∼8.5×106pairs/s/mW/GHz. We quantify the single-photon purity using the second-order autocorrelation function g(2), which reaches the lowest value of ∼(3.4 ± 0.038) × 10−4 for 20 GHz repetition rate pulses, generating heralded single photons at 45 kHz rate. Our all-guided wave configuration offers easy integration and alignment, paving the way for developing scalable, integrable, tunable purity single-photon sources for quantum technology applications, such as quantum communication and quantum networks.