Samuel Guibal

Double-lambda microscopic model for entangled light generation by four-wave-mixing

Motivated by recent experiments, we study four-wave-mixing in an atomic double-{Lambda} system driven by a far-detuned pump. Using the Heisenberg-Langevin formalism, and based on the microscopic properties of the medium, we calculate the classical and quantum properties of seed and conjugate beams beyond the linear amplifier approximation. A continuous-variable approach gives us access to relative-intensity noise spectra that can be directly compared with experiments. Restricting ourselves to the cold-atom regime, we predict the generation of quantum-correlated beams with a relative-intensity noise spectrum well below the standard quantum limit (down to -6 dB). Moreover, entanglement between seed and conjugate beams measured by an inseparability down to 0.25 is expected. This work opens the way to the generation of entangled beams by four-wave mixing in a cold-atom sample.

Experimental versus theoretical rates for photoassociation and for formation of ultracold molecules

We report on the spectra of the long-range attractive molecular states of the Cs/sub 2/ dimer below the dissociation limits 6s+6p/sub 1/2/ and 6s+6p/sub 3/2/ which are accessible by molecular photoassociation of cold Cs atoms. For the states O/sub u//sup +/ and O/sub g//sup -/(6s+6p/sub 3/2/), we have performed trap-loss measurements, which are in good agreement with the theoretical calculations, performed in a perturbative approach. For the O/sub g//sup -/ and 1/sub u/(6s+6p/sub 3/2/) states, we observe, after spontaneous decay of the electronically excited molecules, the formation of translationally cold molecules. A rate of formation of cold molecules of the order of /spl sim/10/sup 6/ molecules per second is obtained in the case of the state O/sub g//sup

Topologically decoherence-protected qubits with trapped ions

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Trapping and cooling of Sr+ ions: strings and large clouds

The authors introduced a new kind of Hamiltonian describing an infinite range coupling between particles placed on a square array with a large number of symmetries and describe its spectral properties. The authors also shows in particular that this Hamiltonian can be naturally realized using ions confined in a surface trap and that the induced protection is more effective than the one predicted for a short range Hamiltonian.

Feasibility of a quantum memory for continuous variables based on trapped ions: from generic criteria to practical implementation

This paper reports on trapping and laser cooling of singly ionized strontium ions in a linear Paul trap. We describe the loading technique based on two-photon absorption of femtosecond pulses at a wavelength of 431 nm and we compare this technique to electron-bombardment ionization. We perform Doppler cooling of the ions in the few-ions regime as well as in the case of large clouds. The analysis of the fluorescence spectra and direct imaging of the cloud allows us to identify the Coulomb-crystal regime. These experiments open the way to the use of a large cold trapped-ion cloud as a medium for quantum optics and quantum information experiments.

Isotope shifts of natural Sr+ measured by laser fluorescence in a sympathetically cooled Coulomb crystal

We propose to use a large cloud of cold trapped ions as a medium for quantum optics and quantum information experiments. Contrary to most recent realizations of qubit manipulation based on a small number of trapped and cooled ions, we study the case of traps containing a macroscopic number of ions. We consider in particular the implementation of a quantum memory for quantum information stored in continuous variables and study the impact of the relevant physical parameters on the expected performances of the system.

Ion microtrap technology for quantum information and precision spectroscopy

We measured by laser spectroscopy the isotope shifts between naturally occurring even isotopes of strontium ions for both the

Precision measurement of the branching fractions of the5pP1/22state inSr+88with a single ion in a microfabricated surface trap

5s\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{S}_{1/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{1/2}

Quantum correlations between intense beams using four-wave mixing in atomic vapours: Theory and experiments

(violet) and the

Quantum correlations by four-wave mixing in an atomic vapor in a nonamplifying regime: Quantum beam splitter for photons

4d\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{3/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{1/2}