Quantum state transfer between field and atoms in Electromagnetically Induced Transparency

We show that a quasi-perfect quantum state transfer between an atomic ensemble and fields in an optical cavity can be achieved in Electromagnetically Induced Transparency (EIT). A squeezed vacuum field state can be mapped onto the long-lived atomic spin associated to the ground state sublevels of the Lambda-type atoms considered. The EIT on-resonance situation show interesting similarities with the Raman off-resonant configuration. We then show how to transfer the atomic squeezing back to the field exiting the cavity, thus realizing a quantum memory-type operation.Comment: 8 pages, 4 figure

Squeezing and entangling nuclear spins in helium 3

We present a realistic model for transferring the squeezing or the entanglement of optical field modes to the collective ground state nuclear spin of $^3$He using metastability exchange collisions. We discuss in detail the requirements for obtaining good quantum state transfer efficiency and study the possibility to readout the nuclear spin state optically

Atomic quantum memory: cavity vs single pass schemes

This paper presents a quantum mechanical treatment for both atomic and field fluctuations of an atomic ensemble interacting with propagating fields, either in Electromagnetically Induced Transparency or in a Raman situation. The atomic spin noise spectra and the outgoing field spectra are calculated in both situations. For suitable parameters both EIT and Raman schemes efficiently preserve the quantum state of the incident probe field in the transfer process with the atoms, although a single pass scheme is shown to be intrinsically less efficient than a cavity scheme

Teleportation of an atomic ensemble quantum state

We propose a protocol to achieve high fidelity quantum state teleportation of a macroscopic atomic ensemble using a pair of quantum-correlated atomic ensembles. We show how to prepare this pair of ensembles using quasiperfect quantum state transfer processes between light and atoms. Our protocol relies on optical joint measurements of the atomic ensemble states and magnetic feedback reconstruction

Dynamics of a pulsed continuous variable quantum memory

We study the transfer dynamics of non-classical fluctuations of light to the ground-state collective spin components of an atomic ensemble during a pulsed quantum memory sequence, and evaluate the relevant physical quantities to be measured in order to characterize such a quantum memory. We show in particular that the fluctuations stored into the atoms are emitted in temporal modes which are always different than those of the readout pulse, but which can nevertheless be retrieved efficiently using a suitable temporal mode-matching technique. We give a simple toy model - a cavity with variable transmission - which accounts for the behavior of the atomic quantum memory.Comment: 6 pages, 5 figure

Non-invasive vibrational mode spectroscopy of ion Coulomb crystals through resonant collective coupling to an optical cavity field

We report on a novel non-invasive method to determine the normal mode frequencies of ion Coulomb crystals in traps based on the resonance enhanced collective coupling between the electronic states of the ions and an optical cavity field at the single photon level. Excitations of the normal modes are observed through a Doppler broadening of the resonance. An excellent agreement with the predictions of a zero-temperature uniformly charged liquid plasma model is found. The technique opens up for investigations of the heating and damping of cold plasma modes, as well as the coupling between them.Comment: 4 pages, 4 figure

Entanglement storage in atomic ensembles

We propose to entangle macroscopic atomic ensembles in cavity using EPR-correlated beams. We show how the field entanglement can be almost perfectly mapped onto the long-lived atomic spins associated with the ground states of the ensembles, and how it can be retrieved in the fields exiting the cavities after a variable storage time. Such a continuous variable quantum memory is of interest for manipulating entanglement in quantum networks

Continuous variable entanglement using cold atoms

We present experimental demonstration of quadrature and polarization entanglement generated via the interaction between a coherent linearly polarized field and cold atoms in a high finesse optical cavity. The non linear atom-field interaction produces two squeezed modes with orthogonal polarizations which are used to generate a pair of non separable beams, the entanglement of which is demonstrated by checking the inseparability criterion for continuous variables recently derived by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)] and calculating the entanglement of formation [Giedke et al., Phys. Rev. Lett. 91, 107901 (2003)]