Coherent-state information concentration and purification in atomic memory

Abstract

We propose a feasible method of coherent-state information concentration and purification utilizing quantum memory. The method allows us to optimally concentrate and purify information carried by many noisy copies of an unknown coherent state (randomly distributed in time) to a single copy. Thus nonclassical resources and operations can be saved, if we compare information processing with many noisy copies and a single copy with concentrated and purified information

Gaussification of quantum states of traveling light beams in atomic memory

“…If we just reduce the coupling strength while keeping it fixed, κ = 1/ √ M , then with appropriate gains we obtain [19],…”

“…Although the present scheme involves quantum memories, it is not a quantum repeater because the memories do not improve the scaling of the success probability of the protocol. However, the quantum memories do enable purification and Gaussification of many copies of entangled states of light emitted at different times [19].…”

“…In this paper we propose and investigate a scheme for Gaussfication of states of traveling light beams mediated by their interaction with atomic quantum memory. The procedure is inspired by protocol for storage of states of light in atomic quantum memory [6] and by scheme for coherent-state information concentration in atomic memory [19]. The scheme involves repeated switching between two different types of QND coupling which ensures that the total QND coupling strength between light and atoms grows only logarithmically with the number of Gaussified light modes M .…”

“…The scheme involves repeated switching between two different types of QND coupling which ensures that the total QND coupling strength between light and atoms grows only logarithmically with the number of Gaussified light modes M . Another appealing feature of the suggested scheme is that the light beams need not be perfectly synchronized and can arrive at different times [19] and the resulting Gaussified state is stored in a memory. This protocol can be used to prepare an atomic memory in an arbitrary Gaussian quantum state.…”