Single-photon-level optical storage in a solid-state spin-wave memory

TL;DR

This paper demonstrates a complete atomic frequency comb quantum memory with spin-wave storage at the single-photon level in a solid-state system, achieving low noise and coherence suitable for quantum repeater applications.

Contribution

First demonstration of spin-wave optical storage at the single-photon level in a solid-state rare-earth-ion-doped system, including detailed experimental procedures.

Findings

Achieved storage of weak coherent pulses with an average photon number of 2.5.

Demonstrated coherence of stored time-bin pulses.

Measured low noise level of 7.1e-3 photons per mode during storage.

Abstract

A long-lived quantum memory is a firm requirement for implementing a quantum repeater scheme. Recent progress in solid-state rare-earth-ion-doped systems justifies their status as very strong candidates for such systems. Nonetheless an optical memory based on spin-wave storage at the single-photon-level has not been shown in such a system to date, which is crucial for achieving the long storage times required for quantum repeaters. In this letter we show that it is possible to execute a complete atomic frequency comb (AFC) scheme, including spin-wave storage, with weak coherent pulses of $\bar{n} = 2.5 \pm 0.6$ photons per pulse. We discuss in detail the experimental steps required to obtain this result and demonstrate the coherence of a stored time-bin pulse. We show a noise level of $(7.1 \pm 2.3)10^{-3}$ photons per mode during storage, this relatively low-noise level paves the way for future quantum optics experiments using spin-waves in rare-earth-doped crystals.