Long-lived quantum memory with nuclear atomic spins

We propose to store non-classical states of light into the macroscopic collective nuclear spin ($10^{18}$ atoms) of a $^3$He vapor, using metastability exchange collisions. These collisions, commonly used to transfer orientation from the metastable state $2^{3}S\_1$ to the ground state state of $^3$He, can also transfer quantum correlations. This gives a possible experimental scheme to map a squeezed vacuum field state onto a nuclear spin state with very long storage times (hours).Comment: 4 page

Observation of metastable hcp solid helium

We have produced and observed metastable solid helium-4 below its melting pressure between 1.1 K and 1.4 K. This is achieved by an intense pressure wave carefully focused inside a crystal of known orientation. An accurate density map of the focal zone is provided by an optical interferometric technique. Depending on the sample, minimum density achieved at focus corresponds to pressures between 2 and 4 bar below the static melting pressure. Beyond, the crystal undergoes an unexpected instability much earlier than the predicted spinodal limit. This opens a novel opportunity to study this quantum crystal in an expanded metastable state and its stability limits.Comment: deuxi\`eme versio

Discovery of dumbbell-shaped Cs*He_n exciplexes in solid He 4

We have observed several new spectral features in the fluorescence of cesium atoms implanted in the hcp phase of solid helium following laser excitation to the 6$^{2}$P states. Based on calculations of the emission spectra using semiempirical Cs-He pair potentials the newly discovered lines can be assigned to the decay of specific Cs*He$_{n}$ exciplexes: an apple-shaped Cs$(A\Pi _{3/2})$He$_{2}$ and a dumbbell-shaped Cs$(A\Pi_{1/2})$He$_{n}$ exciplex with a well defined number $n$ of bound helium atoms. While the former has been observed in other enviroments, it was commonly believed that exciplexes with $n>2$ might not exist. The calculations suggest Cs$(A\Pi_{1/2})$He$_{6}$ to be the most probable candidate for that exciplex, in which the helium atoms are arranged on a ring around the waist of the dumbbell shaped electronic density distribution of the cesium atom.Comment: 4 pages, 4 figure

Search for anisotropic effects of hcp solid helium on optical lines of cesium impurities

The anisotropic effect of a hcp 4He solid matrix on cesium atoms has been proposed as a tool to reveal the parity violating anapole moment of its nucleus. It should also result in splitting the D2 optical excitation line in a way depending on the light polarization. An experimental investigation has been set up using oriented hcp helium crystals in which cesium metal grains are embedded. Atoms are created by laser sputtering from this grains. Optical absorption spectra of the D2 line have been recorded in the temperature range of 1.0 to 1.4 K at liquid/solid coexistence pressure by monitoring the fluorescence on the D2 line at 950 nm. No significant effect of the light polarization has been found, suggesting a statistically isotropic disordered solid environment for the cesium atoms.Comment: The original publication will be available at http://www.springerlink.co

Prewetting transition on a weakly disordered substrate : evidence for a creeping film dynamics

We present the first microscopic images of the prewetting transition of a liquid film on a solid surface. Pictures of the local coverage map of a helium film on a cesium metal surface are taken while the temperature is raised through the transition. The film edge is found to advance at constant temperature by successive avalanches in a creep motion with a macroscopic correlation length. The creep velocity varies strongly in a narrow temperature range. The retreat motion is obtained only at much lower temperature, conforming to the strong hysteresis observed for prewetting transition on a disordered surface. Prewetting transition on such disordered surfaces appears to give rise to dynamical phenomena similar to what is observed for domain wall motions in 2D magnets.Comment: 7 pages, 3 figures, to be published in Euro.Phys.Let

Probing vortices in 4He nanodroplets

We present static and dynamical properties of linear vortices in 4He droplets obtained from Density Functional calculations. By comparing the adsorption properties of different atomic impurities embedded in pure droplets and in droplets where a quantized vortex has been created, we suggest that Ca atoms should be the dopant of choice to detect vortices by means of spectroscopic experiments.Comment: Typeset using Revtex4, 4 pages and 2 Postscript file

Static Response Function for Longitudinal and Transverse Excitations in Superfluid Helium

The sum rule formalism is used to evaluate rigorous bounds for the density and current static response functions in superfluid helium at zero temperature. Both lower and upper bounds are considered. The bounds are expressed in terms of ground state properties (density and current correlation funtions) and of the interatomic potential. The results for the density static response significantly improve the Feynman approximation and turn out to be close to the experimental (neutron scattering) data. A quantitative prediction for the transverse current response is given. The role of one-phonon and multi-particle excitations in the longitudinal and transverse channels is discussed. (Phys.Rev.B, in press)Comment: 19 pages (plain TeX) and 3 Figures (postscript), UTF-26

Collective Modes in a Slab of Interacting Nuclear Matter: The effects of finite range interactions

We consider a slab of nuclear matter and investigate the collective excitations, which develop in the response function of the system. We introduce a finite-range realistic interaction among the nucleons, which reproduces the full G-matrix by a linear combination of gaussian potentials in the various spin-isospin channels. We then analyze the collective modes of the slab in the S=T=1 channel: for moderate momenta hard and soft zero-sound modes are found, which exhaust most of the excitation strength. At variance with the results obtained with a zero range force, new "massive" excitations are found for the vector-isovector channel .Comment: 14 pages, TeX, 5 figures (separate uuencoded and tar-compressed postscript files), Torino preprint DFTT 6/9

Dual channel self-oscillating optical magnetometer

We report on a two-channel magnetometer based on nonlinear magneto-optical rotation in a Cs glass cell with buffer gas. The Cs atoms are optically pumped and probed by free running diode lasers tuned to the D$_2$ line. A wide frequency modulation of the pump laser is used to produce both synchronous Zeeman optical pumping and hyperfine repumping. The magnetometer works in an unshielded environment and spurious signal from distant magnetic sources is rejected by means of differential measurement. In this regime the magnetometer simultaneously gives the magnetic field modulus and the field difference. Rejection of the common-mode noise allows for high-resolution magnetometry with a sensitivity of \pthz{2}. This sensitivity, in conjunction with long-term stability and a large bandwidth, makes possible to detect water proton magnetization and its free induction decay in a measurement volume of 5 cm$^3$Comment: 13 pages, 9 figures. Improved version (v2). Accepted for publicatio

A Single Charged Quantum Dot in a Strong Optical Field: Absorption, Gain, and the AC Stark Effect

We investigate a singly-charged quantum dot under a strong optical driving field by probing the system with a weak optical field. When the driving field is detuned from the trion transition, the probe absorption spectrum is shifted from the trion resonance as a consequence of the dynamic Stark effect. Simultaneously, a gain sideband is created, resulting from the coherent energy transfer between the optical fields through the quantum dot nonlinearity. As the pump detuning is moved from red to blue, we map out the anticrossing of these two spectral lines. The optical Bloch equations for a stationary two-level atom can be used to describe the numerous spectral features seen in this nano solid state system