Why the two-pulse photon echo is not a good quantum memory protocol

Abstract

We consider in this paper a two-pulse photon echo sequence as a potential quantum light storage protocol. It is widely believed that a two-pulse scheme should lead to very low efficiency and is then not relevant for this specific application. We show experimentally by using a Tm${}^{3+}$:YAG crystal that such a protocol is on contrary very efficient and even too efficient to be considered as a good quantum storage protocol. Our experimental work allows us to point out on one side the real limitations of this scheme and on the other side its benefits which can be a source of inspiration to conceive more promising procedures with rare-earth ion doped crystals

Towards an efficient atomic frequency comb quantum memory

“…REICs are characterized by large optical inhomogeneous broadening which enables storage and recall of coherent information by manipulating and controlling the inhomogeneous dephas-ing using echo techniques. Although traditional photon echoes cannot readily be used in the single-photon regime due to spontaneous-emission noise induced by the π-pulse [12], photon echo techniques avoiding this noise have been proposed; controlled reversible inhomogeneous broadening (CRIB) [13,14,15,16,17] and more recently atomic frequency combs (AFC) [18]. The AFC protocol may offer a breakthrough for the practical construction of quantum repeaters capable of achieving sufficient entanglement distribution rate, since the number of modes that can be stored in an AFC QM is independent of the memory material absorption depth.…”

Impossibility of faithfully storing single photons with the three-pulse photon echo

“…This is a major difference compared to genuine quantum memory protocols such as stopped light based on electromagnetically induced transparency (EIT) [13], controlled reversible inhomogeneous broadening (CRIB) [14][15][16][17], or atomic frequency combs (AFC) [18], where the control pulses transfer a negligible number of atoms to excited states. Note finally that additional detrimental effects due to propagation [5] could further limit the fidelity and the efficiency of quantum storage based on three-pulse photon echo.…”

“…Note that other detrimental effects due to the propagation within the atomic ensemble (free-induction decay resulting in the propagation of intense light pulses in the atomic medium or the finite value of the optical depth) further limit the efficiency [5]. Let us now compare I echo with the incoherent emission from the same sample.…”

“…It has been shown already that the simplest form of the photon echo, namely the two-pulse photon echo, is not suited for quantum storage [5]. However, a recent paper [6] might let us believe, at first sight, that the photon echo in its three-pulse version could be used for the storage of light at the single-photon level.…”

Temporal compression of quantum-information-carrying photons using a photon-echo quantum memory approach

“…We point out that optical pulse compression has previously been considered using traditional photon echos and chirped excitation pulses [11][12][13]. However, similar to data storage [14,15], this approach is not suitable for temporal compression of quantum data. Quantum compression using CRIB has first been discussed in [16], and first observations as well as numerical studies for the case of longitudinal broadening have recently been reported [17,18].…”