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arXiv · 2205.13778

Temporally-ultralong biphotons with a linewidth of 50 kHz

Yu-Sheng Wang·Kai-Bo Li·Chao-Feng Chang·Tan-Wen Lin·Jian-Qing Li·Shih-Si Hsiao·Jia-Mou Chen·Yi-Hua Lai·Ying-Cheng Chen·Yong-Fan Chen·Chih-Sung Chuu·Ite A. Yu
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Abstract

We report the generation of biphotons, with a temporal full width at the half maximum (FWHM) of 13.4$\pm$0.3 $\mu$s and a spectral FWHM of 50$\pm$1 kHz, via the process of spontaneous four-wave mixing. The temporal width is the longest, and the spectral linewidth is the narrowest up to date. This is also the first biphoton result that obtains a linewidth below 100 kHz, reaching a new milestone. The very long biphoton wave packet has a signal-to-background ratio of 3.4, which violates the Cauchy-Schwarz inequality for classical light by 4.8 folds. Furthermore, we demonstrated a highly-tunable-linewidth biphoton source and showed that while the biphoton source's temporal and spectral width were controllably varied by about 24 folds, its generation rate only changed by less than 15\%. A spectral brightness or generation rate per pump power per linewidth of 1.2$\times$10$^6$ pairs/(s$\cdot$mW$\cdot$MHz) was achieved at the temporal width of 13.4 $\mu$s. The above results were made possible by the low decoherence rate and high optical depth of the experimental system, as well as the nearly phase-mismatch-free scheme employed in the experiment. This work has demonstrated a high-efficiency ultranarrow-linewidth biphoton source, and has made a substantial advancement in the quantum technology utilizing heralded single photons.

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Yu-Sheng Wang, Kai-Bo Li, Chao-Feng Chang, Tan-Wen Lin, Jian-Qing Li, Shih-Si Hsiao, Jia-Mou Chen, Yi-Hua Lai, Ying-Cheng Chen, Yong-Fan Chen, Chih-Sung Chuu, Ite A. Yu. 2022-05-27. Temporally-ultralong biphotons with a linewidth of 50 kHz. https://doi.org/10.1063/5.0102393

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