Fast storage of photons in cavity-assisted quantum memories

TL;DR

This paper presents a theoretical analysis and optimization strategy for cavity-assisted quantum memories that improves storage efficiency for short, non-adiabatic photon pulses, enhancing quantum information storage capabilities.

Contribution

It introduces an analytical protocol for optimizing quantum memory efficiency across various pulse durations, surpassing previous numerical methods.

Findings

Efficiency depends on pulse shape and duration.

Optimal strategies improve storage performance in non-adiabatic regimes.

Efficiency is limited by pulse width or shape at storage/retrieval boundaries.

Abstract

Ideal photonic quantum memories can store arbitrary pulses of light with unit efficiency. This requires operating in the adiabatic regime, where pulses have a duration much longer than the bandwidth of the memory. In the non-adiabatic regime of short pulses, memories are therefore imperfect, and information is always lost. We theoretically investigate the bandwidth limitations for setups based on individual atoms, or ensembles thereof, confined inside optical cavities. We identify an effective strategy for optimizing the efficiencies of the storage and retrieval process regardless of the duration of the pulses. Our protocol is derived almost completely analytically and attains efficiencies better than or comparable to those obtained by numerical optimization. Furthermore, our results provide an improved understanding of the performance of quantum memories in several regimes. When considering pulses defined on an infinite time interval, the shapes can be divided into two categories, depending on their asymptotic behaviours. If the intensity of the pulse increases with time slower than or as an exponential function, then the storage efficiency is only limited by the pulse width. For pulses defined on a finite interval, on the other hand, the efficiency is determined by the shape at the beginning of the storage or, correspondingly, at the end of the retrieval process.