Rephasing processes and quantum memory for light: reversibility issues and how to fix them

TL;DR

This paper investigates the reversibility issues in AFC quantum memory protocols, identifies spectral dispersion as a cause for efficiency loss, and proposes a modified scheme to restore reversibility and improve performance.

Contribution

It introduces a modified AFC scheme that restores reversibility, enabling high-efficiency quantum memory retrieval across the entire bandwidth.

Findings

Reversibility issues cause efficiency loss in AFC memory.

Spectral dispersion leads to phase mismatching.

Modified AFC scheme restores reversibility and efficiency.

Abstract

Time reversibility is absent from some recently proposed quantum memory protocols such as Absorption Frequency Comb (AFC). Focusing on AFC memory, we show that quantum efficiency and fidelity are reduced dramatically, as a consequence of non-reversibility, when the spectral width of the incoming signal approaches the memory bandwidth. Non-reversibility is revealed through spectral dispersion, giving rise to phase mismatching. We propose a modified AFC scheme that restores reversibility. This way, signals can be retrieved with excellent efficiency over the entire memory bandwidth. This study could be extended to other quantum memory rephasing schemes in inhomogeneously broadened absorbing media.