Two-step frequency conversion for connecting distant quantum memories by transmission through an optical fiber

TL;DR

This paper introduces a novel two-step frequency conversion process enabling the connection of distant quantum memories via optical fibers, crucial for long-distance quantum communication.

Contribution

It demonstrates the first experimental implementation of a two-step frequency conversion system for nitrogen-vacancy centers, achieving about 7% efficiency and analyzing noise characteristics.

Findings

Achieved approximately 7% total conversion efficiency.

Measured and characterized noise and signal-to-noise ratio.

Showcased potential for quantum repeater networks using optical fibers.

Abstract

Long-distance quantum communication requires entanglement between distant quantum memories. For this purpose, photon transmission is necessary to connect the distant memories. Here, for the first time, we develop a two-step frequency conversion process (from a visible wavelength to a telecommunication wavelength and back) involving the use of independent two-frequency conversion media where the target quantum memories are nitrogen-vacancy centers in diamonds (with an emission/absorption wavelength of 637.2 nm), and experimentally characterize the performance of this process acting on light from an attenuated CW laser. A total conversion efficiency of approximately 7% is achieved. The noise generated in the frequency conversion processes is measured, and the signal-to-noise ratio is estimated for a single photon signal emitted by a nitrogen-vacancy (NV) center. The developed frequency conversion system has future applications via transmission through a long optical fiber channel at a telecommunication wavelength for a quantum repeater network.