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Chinese Physics B

Improving the spectral purity of single photons by a single-interferometer-coupled microring

Yang Wang, Pingyu Zhu, Shichuan Xue, Yingwen Liu, Junjie Wu, Xuejun Yang, Ping Xu

Published Nov 4, 2021• 0 citations
Publisher

Abstract

We experimentally engineer a high-spectral-purity single-photon source using a single-interferometer-coupled silicon microring. By the reconfiguration of the interferometer, different coupling conditions can be obtained, corresponding to different quality factors for the pump and signal/idler. The ratio between the quality factor of the pump and signal/idler ranges from 0.29 to 2.57. By constructing the signal–idler joint spectral intensity, we intuitively demonstrate the spectral correlation of the signal and idler. As the ratio between the quality factor of the pump and signal/idler increases, the spectral correlation of the signal and idler decreases, i.e., the spectral purity of the signal/idler photons increases. Furthermore, time-integrated second-order correlation of the signal photons is measured, giving a value up to 94.95 ± 3.46%. Such high-spectral-purity photons will improve the visibility of quantum interference and facilitate the development of on-chip quantum information processing.

DOI
10.1088/1674-1056/ac3652

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We experimentally engineer a high-spectral-purity single-photon source using a single-interferometer-coupled silicon microring. By the reconfiguration of the interferometer, different coupling conditions can be obtained, corresponding to different quality factors for the pump and signal/idler. The ratio between the quality factor of the pump and signal/idler ranges from 0.29 to 2.57. By constructing the signal–idler joint spectral intensity, we intuitively demonstrate the spectral correlation of the signal and idler. As the ratio between the quality factor of the pump and signal/idler increases, the spectral correlation of the signal and idler decreases, i.e., the spectral purity of the signal/idler photons increases. Furthermore, time-integrated second-order correlation of the signal photons is measured, giving a value up to 94.95 ± 3.46%. Such high-spectral-purity photons will improve the visibility of quantum interference and facilitate the development of on-chip quantum information processing.
We experimentally demonstrate a high-spectral-purity photon source by designing a dual-Mach–Zehnder-interferometer-coupled silicon ring resonator, wherein the linewidths of pump and signal (idler) resonances can be engineered independently. A high spectral purity of 95 % ± 1.5 % is obtained via a time-integrated g ( 2 ) correlation measurement, which exceeds the theoretical 93% bound of a traditional ring’s spontaneous four-wave-mixing photon source. This source also possesses high performance in other metrics including a measured coincidence of 9599 pairs/s and a preparation heralding efficiency of 52.4% at a relatively low pump power of 61 µW as well as high drop-to-through suppression of 20.2 dB. By overcoming the trade-off between spectral purity and brightness in the post-filtering way, such a method guarantees bright pure photons and will pave the way for development of on-chip quantum information processing with improved operation fidelity and efficiency.
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We demonstrate that an integrated silicon microring resonator is capable of efficiently producing photon pairs that are completely unentangled; such pairs are a key component of heralded single-photon sources. A dual-channel interferometric coupling scheme can be used to independently tune the quality factors associated with the pump and signal and idler modes, yielding a biphoton wavefunction with a Schmidt number arbitrarily close to unity. This will permit the generation of heralded single-photon states with unit purity.
Recently, many researchers focus on the integration of single photon sources on an optical chip toward the realization of large-scale quantum information processing.Identical single photons are required to obtain good interference between photons for quantum information processing, for which high "spectral purity" of single photons is required.An appealing scheme is employing the spontaneous four-wave mixing (SFWM) in a silicon micro-ring resonator (MRR) because it allows us to generate high-purity photons without external spectral filters.However, the purity value is limited to 0.92 due to the dispersion property of an MRR We have developed a new scheme to further increase the spectral purity from an MRR by manipulating the spectral phase distribution of the pump pulse.Via exploring several strategies on the spectral phase modulation, we found that the purity of single photon can be increased up to approximately 0.96 breaking the conventional limitation of 0.92 in a standard MRR.We further explore the experimental feasibility of the scheme toward future implementation.
High-visibility quantum interference between independent photons is essential for demonstrating multi-photon quantum information processing, and it is closely linked to the spectral purity of correlated photon pairs. In this study, we investigate two approaches to enhance the purity of photon pairs generated from a type-0 PPLN waveguide by systematically varying both the pump bandwidth and the interference-filter bandwidth, and we directly compare their performance under identical experimental conditions. The spectral purity is evaluated from measured joint spectral intensities using Schmidt decomposition. Both methods significantly improve the Hong-Ou-Mandel interference visibility to approximately 80%. However, the former approach also yields a higher three-fold coincidence rate, which is advantageous for our ongoing efforts to increase the state fidelity and generation rate of multi-photon time-bin Greenberger-Horne-Zeilinger (GHZ) states.