Optimising the Efficiency of a Quantum Memory based on Rephased Amplified Spontaneous Emission

TL;DR

This paper investigates the efficiency of a quantum memory protocol based on rephased amplified spontaneous emission in a rare-earth doped crystal, achieving improved rephasing efficiency and analyzing limiting factors.

Contribution

The study demonstrates enhanced rephasing efficiency in a quantum memory protocol using RASE in Pr$^{3+}$:Y$_{2}$SiO$_{5}$ and discusses mechanisms limiting performance.

Findings

Maximum rephasing efficiency of 14% observed with spin storage.

Rephased emission observed at optical depths 0.8 to 2.0.

Efficiency surpasses previous non-classical results but remains below theoretical predictions.

Abstract

We studied the recall efficiency as a function of optical depth of rephased amplified spontaneous emission (RASE), a protocol for generating entangled light. The experiments were performed on the $^{3}\! H_{4}$ $\rightarrow$ $^{1}\! D_{2}$ transition in the rare-earth doped crystal Pr$^{3+}$:Y$_{2}$SiO$_{5}$, using a four-level echo sequence between four hyperfine levels to rephase the emission. Rephased emission was observed for optical depths in the range of $\alpha L$ = 0.8 to 2.0 with a maximum rephasing efficiency of 14 % observed while incorporating spin storage. This efficiency is a significant improvement over the previously reported non-classical result but is well short of the predicted efficiency. We discuss the possible mechanisms limiting the protocol's performance, and suggest ways to overcome these limits.