Optical quantum memory with generalized time-reversible atom–light interaction

Abstract

We examine a quantum memory scheme based on controllable dephasing of atomic coherence of a non-resonant, inhomogeneously broadened Raman transition. We show that it generalizes the physical conditions for time-reversible interaction between light and atomic ensembles from weak to strong fields and from linear to non-linear interactions. We also develop a unified framework for different realizations exploiting either controlled reversible inhomogeneous broadening or atomic frequency combs, and discuss new aspects related to storage and manipulation of quantum states.PACS numbers: 03.67. 42.50.Ct, 42.50.Md The study of time-reversible evolution of physical systems was central in the development of thermodynamics and statistical mechanics [1], and CPT symmetry [2]. Furthermore, reversible interaction underpins reversible transfer of quantum states between light and atoms, i.e. quantum memory (QM), which is key for quantum repeaters [3] and all-optical quantum computing [4].Approaches to QM exploit atoms in cavities [6], nonresonant Raman transitions [7,8], electromagnetically induced transparency [9,10,11,12,13,14,15], or photonecho techniques [16,17,18,19,20,21,22,23]. The latter is of particular interest in the present context, as the equations of motion include a hidden time-reversal symmetry [18]. It has, however, so far only been discussed for weak light fields. Here we generalize the physical conditions allowing for time-reversal symmetry in the mapping of quantum states between light and atomic ensembles to fields of arbitrary strength and non-linear interactions. The scheme exploits reversible dephasing of atomic coherence of a non-resonant, inhomogeneously broadened Raman transition (Raman Echo Quantum Memory or REQM). It has been proposed in [24], further developed in [25,27], and first demonstrated in [28]. We also compare the conditions for time-reversibility for storage of strong fields with those for weak fields, which naturally leads to a unified framework for realizations of REQM based on controlled reversible inhomogeneous broadening (CRIB) [18] or atomic frequency combs (AFC) [22]. Our findings shed new light on time-reversibility in the interaction between light and inhomogeneously broadened atomic ensembles, and also pave the road to storage of macroscopic light fields in nano-sized atomic media. Furthermore, we discuss with the example of frequency conversion how REQM enables controlled manipulation of quantum light fields.The scheme: Energy and temporal diagrams of the interaction scheme are depicted in Fig.1. At time t=0 the probe light fieldÊ 1 (t, z) with duration δt 1 , carrier frequency ω 1 and spectral width δω 1 = δt −1

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“…The cancellation of the dispersion by using oppositely detuned transitions produces a time-reversal symmetry in the equations of motion. This is detailed by Moiseev and Tittel [54], and was useful in interpreting the dynamics of our system. We use a large (3") aperture lens to image the MOT onto a CCD camera.…”

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