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

TL;DR

This paper demonstrates a cavity-enhanced quantum frequency converter that improves signal-to-noise ratio for converting single photons from visible to telecom wavelengths, maintaining quantum properties without external narrowband filters.

Contribution

The study introduces a compact cavity-enhanced QFC device that boosts conversion efficiency and noise suppression, enabling high-quality quantum frequency conversion with simplified filtering.

Findings

Achieved efficient frequency conversion from 780 nm to 1540 nm.

Maintained non-classical photon statistics after conversion.

Demonstrated comparable signal-to-noise ratio with cavity and external filtering.

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. For the QFC based on the frequency downconversion from visible to the telecom wavelengths around 1500 nm, it is widely known that noise photons produced by the strong pump light used for QFC contaminate the frequency-converted photon, which degrades the quality of the quantum property of the photon after QFC. In conventional QFC experiments, noise photons are removed using external narrowband frequency filter systems. In contrast, in this study, we implement a compact QFC device integrating the cavity structure only for the converted mode. While the cavity structure can enhance not only the desired QFC efficiency but also the noise photon generation rate, we show that the cavity-enhanced QFC followed by a relatively wide bandpass filter achieves the signal-to-noise ratio comparable to the QFCs with external narrowband filters. We experimentally demonstrate the cavity-enhanced QFC using a single photon at 780 nm to 1540 nm, in which the non-classical photon statistics is clearly observed after QFC.