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Quantum Nanophotonic Materials, Devices, and Systems

Bright heralded source based on SWFM reaching theoretical single-photon purity

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

Published Aug 16, 2024• 0 citations
Publisher

Abstract

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.

DOI
10.1117/12.3023057

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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.
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.
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.
Single photon sources by heralding time correlated photons are described. By intermodal four wave mixing (FWM) in a silicon photon circuit, we generate a herald photon at 1260 nm and the heralded one beyond 2 um, with a coincidence to accidental ratio larger than 50 and a single photon purity of 0.75. The discrete band intermodal phase matching does not require further filtering to improve the purity of the single photon. Moreover, the intermodal FWM exhibits high controllability of the signal/idler wavelengths, that can be generated far from the Raman and pump noise, with improved noise filtering.
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.