Prospective applications of optical quantum memories

Abstract

An optical quantum memory can be broadly defined as a system capable of storing a useful quantum state through interaction with light at optical frequencies. During the last decade, intense research was devoted to their development, mostly with the aim of fulfilling the requirements of their first two applications, namely quantum repeaters and linear-optical quantum computation. A better understanding of those requirements then motivated several different experimental approaches. Along the way, other exciting applications emerged, such as as quantum metrology, single-photon detection, tests of the foundations of quantum physics, deviceindependent quantum information processing and nonlinear processing of quantum information. Here we review several prospective applications of optical quantum memories with a focus on recent experimental achievements pertaining to these applications. This review highlights that optical quantum memories have become essential for the development of optical quantum information processing.

An artificial Rb atom in a semiconductor with lifetime-limited linewidth

“…Independently, atomic ensembles have developed into one of the best platforms for optical quantum memories [10,11]. The combination of strong absorption and long ground state hyperfine coherence has allowed storage times of miliseconds and efficiencies higher than 75% to be achieved in these systems [12][13][14][15].…”

Solid-state Raman quantum memory in whispering gallery mode resonators: signal-to-noise ratio

“…(see [1,2] for a recent review). One of the most commonly discussed materials are rare-earth-ion-doped solids [3], in which the phase relaxation time at cryogenic temperatures may be as long as several hours [4].…”

Preparation of single-photon states via cavity-assisted spontaneous parametric down-conversion for quantum memory based on Y7LiF4:Nd3+ crystal

“…For getting through the fibre losses and implementing long-distance quantum communication protocols, one can take advantage of quantum repeaters [1,2], which in turn requires storage of nonclassical light states in a quantum memory device. Among different schemes of quantum memory (see, e.g., recent reviews [3,4]), off-resonant solid-state Raman schemes might be useful. In this respect, isotopically pure crystal Y 7 LiF4:Nd 3+ seems to be one of the promising materials [5,6].…”