Revival of Silenced Echo and Quantum Memory for Light

We propose an original quantum memory protocol. It belongs to the class of rephasing processes and is closely related to two-pulse photon echo. It is known that the strong population inversion produced by the rephasing pulse prevents the plain two-pulse photon echo from serving as a quantum memory scheme. Indeed gain and spontaneous emission generate prohibitive noise. A second $\pi$-pulse can be used to simultaneously reverse the atomic phase and bring the atoms back into the ground state. Then a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise. However, one must kill the primary echo, in order to preserve all the information for the secondary signal. In the present work, spatial phase mismatching is used to silence the standard two-pulse echo. An experimental demonstration is presented.Comment: 13 pages, 6 figure

Optical measurement of heteronuclear cross-relaxation interactions in Tm:YAG

We investigate cross-relaxation interactions between Tm and Al in Tm:YAG using two optical methods: spectral holeburning and stimulated echoes. These interactions lead to a reduction in the hyperfine lifetime at magnetic fields that bring the Tm hyperfine transition into resonance with an Al transition. We develop models for measured echo decay curves and holeburning spectra near a resonance, which are used to show that the Tm-Al interaction has a resonance width of 10~kHz and reduces the hyperfine lifetime to 0.5 ms. The antihole structure is consistent with an interaction dominated by the Al nearest neighbors at 3.0 Angstroms, with some contribution from the next nearest neighbors at 3.6 Angstroms.Comment: 13 pages, 9 figure

Numerical and experimental investigations of vector soliton bound-states in a Kerr planar waveguide

We investigate both numerically and experimentally the stability of a vector three-soliton bound state in a Kerr CS2 planar waveguide using the circular polarizations as the two-component of the multimode vector soliton (MVS). The molecular-reorientation-induced Kerr nonlinearity of CS2 leads in this case to a strength of cross-phase modulation that is 7 times larger than that of self-phase modulation. We demonstrate that, under these conditions, the MVS exhibits symmetry-breaking instability leading to different output intensity patterns ranging from three to one-hump vector solitons

Isotropization of Bianchi-Type Cosmological Solutions in Brans-Dicke Theory

The cosmic, general analitic solutions of the Brans--Dicke Theory for the flat space of homogeneous and isotropic models containing perfect, barotropic, fluids are seen to belong to a wider class of solutions --which includes cosmological models with the open and the closed spaces of the Friedmann--Robertson--Walker metric, as well as solutions for models with homogeneous but anisotropic spaces corresponding to the Bianchi--Type metric clasification-- when all these solutions are expressed in terms of reduced variables. The existence of such a class lies in the fact that the scalar field, $\phi$, times a function of the mean scale factor or ``volume element'', $a^3 = a_1 a_2 a_3$, which depends on time and on the barotropic index of the equation of state used, can be written as a function of a ``cosmic time'' reduced in terms of another function of the mean scale factor depending itself again on the barotropic index but independent of the metrics here employed. This reduction procedure permites one to analyze if explicitly given anisotropic cosmological solutions ``isotropize'' in the course of their time evolution. For if so can happen, it could be claimed that there exists a subclass of solutions that is stable under anisotropic perturbations.Comment: 15 pages, Late

Superconductivity in a spin liquid - a one dimensional example

We study a one-dimensional model of interacting conduction electrons with a two-fold degenerate band away from half filling. The interaction includes an on-site Coulomb repulsion and Hund's rule coupling. We show that such one-dimensional system has a divergent Cooper pair susceptibility at T = 0, provided the Coulomb interaction $U$ between electrons on the same orbital and the modulus of the Hund's exchange integral $|J|$ are larger than the interorbital Coulomb interaction. It is remarkable that the superconductivity can be achieved for {\it any} sign of $J$. The opening of spectral gaps makes this state stable with respect to direct electron hopping between the orbitals. The scaling dimension of the superconducting order parameter is found to be between 1/4 (small $U$) and 1/2 (large $U$).Comment: 11 pages, Latex, no figure

Perturbations of the local gravity field due to mass distribution on precise measuring instruments: a numerical method applied to a cold atom gravimeter

We present a numerical method, based on a FEM simulation, for the determination of the gravitational field generated by massive objects, whatever geometry and space mass density they have. The method was applied for the determination of the self gravity effect of an absolute cold atom gravimeter which aims at a relative uncertainty of 10-9. The deduced bias, calculated with a perturbative treatment, is finally presented. The perturbation reaches (1.3 \pm 0.1) \times 10-9 of the Earth's gravitational field.Comment: 12 pages, 7 figure

Far-infrared vibrational properties of linear C60 polymers: A comparison between neutral and charged materials

We report the far-infrared transmittance spectrum of a pure phase of the orthorhombic high-temperature and high-pressure C-60 polymer and compare the results with a previously published spectrum of the charged RbC60 orthorhombic polymer. Assignments for both spectra are made with the aid of first-principles quantum molecular dynamics simulations of the two materials. We find that the striking spectral differences between the neutral and charged linear fullerene polymers can be fully accounted for by charge effects on the C-60 ball

Precision atomic gravimeter based on Bragg diffraction

We present a precision gravimeter based on coherent Bragg diffraction of freely falling cold atoms. Traditionally, atomic gravimeters have used stimulated Raman transitions to separate clouds in momentum space by driving transitions between two internal atomic states. Bragg interferometers utilize only a single internal state, and can therefore be less susceptible to environmental perturbations. Here we show that atoms extracted from a magneto-optical trap using an accelerating optical lattice are a suitable source for a Bragg atom interferometer, allowing efficient beamsplitting and subsequent separation of momentum states for detection. Despite the inherently multi-state nature of atom diffraction, we are able to build a Mach-Zehnder interferometer using Bragg scattering which achieves a sensitivity to the gravitational acceleration of $\Delta g/g = 2.7\times10^{-9}$ with an integration time of 1000s. The device can also be converted to a gravity gradiometer by a simple modification of the light pulse sequence.Comment: 13 pages, 11 figure