A continuous-variable quantum memory for light

We study here a different scheme involving a large ensemble of Lambda-type atoms, a control field, and the field to be stored and show how to transfer with a nearly 100% efficiency a quantum state of light (squeezed vacuum) into the ground state coherence of a spin-polarized atomic cloud. We find the best transfer conditions between the two oscillators. The quantum states are well conserved in two seemingly different situations: in the so-called electromagnetically-induced-transparency (EIT) situation (on one-and two-photon resonance) and in a Raman configuration (on two-photon resonance, but for large one-photon detunings). If both situations share interesting similarities in terms of transfer efficiency, and noise spectra, the physical effects responsible for the ideal mapping are quite different, and make the use of both room-temperature and cold atoms possible.