Low-noise quantum frequency conversion with cavity enhancement of the converted mode

Shoichi Murakami, Toshiki Kobayashi, Shigehito Miki, Hirotaka Terai, Tsuyoshi Kodama, Tsuneaki Sawaya, Akihiko Ohtomo, Hideki Shimoi, Takashi Yamamoto, and Rikizo Ikuta

Abstract

Quantum frequency conversion (QFC), which converts the frequencies of photons while preserving the quantum state, is an essential technology for realizing the quantum internet and quantum interconnect. In the QFC from the visible to the telecom wavelengths around 1.5 µm, it is widely known that noise photons produced by the strong pump light used for the process contaminate the frequency-converted photon. It degrades the quality of the quantum property of the output photon. Conventional experiments have employed external narrowband frequency filters to eliminate the noise photons. In this study, we present a compact QFC device integrating the cavity structure only for the converted mode. While the cavity structure enhances both the desired efficiency and the noise photon generation, we show that the cavity-enhanced QFC followed by a relatively wide bandpass filter achieves a signal-to-noise ratio (SNR) comparable to conventional systems using external narrowband filters. We experimentally demonstrate the cavity-enhanced QFC for a single photon, converting it from 780 nm to 1540 nm, and successfully observe the non-classical photon statistics after conversion.