Focus on Quantum Memory

Abstract

Quantum memories are essential for quantum information processing and long-distance quantum communication. The field has recently seen a lot of progress, and the present focus issue offers a glimpse of these developments, showing both experimental and theoretical results from many of the leading groups around the world. On the experimental side, it shows work on cold gases, warm vapors, rare-earth ion doped crystals and single atoms. On the theoretical side there are in-depth studies of existing memory protocols, proposals for new protocols including approaches based on quantum error correction, and proposals for new applications of quantum storage. Looking forward, we anticipate many more exciting results in this area.

Experimental investigation of practical unforgeable quantum money

“…Our construction allows us to formulate conditions for correctness and security that can be experimentally tested. In particular, we derive conditions in scenarios of practical interest, corresponding to quantum memories based on single emitters or on atomic ensembles, [20][21][22] and to implementations with weak coherent states. In all cases, we demonstrate that these conditions are rigorously satisfied experimentally using a practical photonic setup based on polarization encoding of weak coherent states of light, and we analyze operational regimes where unforgeability is guaranteed.…”

Zero-dynamics principle for perfect quantum memory in linear networks

“…Because of this scientific/technological importance, the field of quantum memory has experienced significant progress in both theory and experiment. We refer to for instance [9][10][11] for reviewing the current situation of this very active research area. Now let us see a basic and general schematic of an ideal quantum memory in an abstract way.…”

Spin frequency comb echo memory controlled by a pulsed-gradient of magnetic field

“…There are a number of echo-based QM protocols intensively elaborated during last decade [7][8][9], such as originally proposed controlled reversible inhomogeneous broadening (CRIB) [10] and its successful particular realizationgradient echo memory (GEM) [11], atomic frequency comb (AFC) [12,13]-provided broadened quantum storage and novel protocols [14,15], using even natural inhomogeneous broadening (silent echo). Thus, the photon (spin) echo approach provides wide experimental opportunities for elaboration of new QM technique that gives a hope for further progress in realization of more efficient QMs.…”

“…Recently, a series of impressive experiments on broadband optical storage has been performed with the help of the AFC protocol [25][26][27][28] on the inorganic crystals doped with rare-earth ions while the largest experimentally realized finesse of AFC structure is still remaining about f ∼ 8 [29]. A lot of experimental results on AFC protocol have been obtained on the optical resonant transitions (see for example [9]). At the same time, this QM technique can also be realized on off-resonant optical Raman transitions [30] and on the microwave resonant transitions between electron-spin states.…”