Phase diagram of the three-dimensional Hubbard model at half filling

We investigate the phase diagram of the three-dimensional Hubbard model at half filling using quantum Monte Carlo (QMC) simulations. The antiferromagnetic Neel temperature T_N is determined from the specific heat maximum in combination with finite-size scaling of the magnetic structure factor. Our results interpolate smoothly between the asymptotic solutions for weak and strong coupling, respectively, in contrast to previous QMC simulations. The location of the metal-insulator transition in the paramagnetic phase above T_N is determined using the electronic compressibility as criterion.Comment: 6 pages, 6 figures, to be published in Eur. Phys. J. B (2000

Saturation of Cs2 Photoassociation in an Optical Dipole Trap

We present studies of strong coupling in single-photon photoassociation of cesium dimers using an optical dipole trap. A thermodynamic model of the trap depletion dynamics is employed to extract absolute rate coefficents. From the dependence of the rate coefficient on the photoassociation laser intensity, we observe saturation of the photoassociation scattering probability at the unitarity limit in quantitative agreement with the theoretical model by Bohn and Julienne [Phys. Rev. A, 60, 414 (1999)]. Also the corresponding power broadening of the resonance width is measured. We could not observe an intensity dependent light shift in contrast to findings for lithium and rubidium, which is attributed to the absence of a p or d-wave shape resonance in cesium

Interference of multi-mode photon echoes generated in spatially separated solid-state atomic ensembles

High-visibility interference of photon echoes generated in spatially separated solid-state atomic ensembles is demonstrated. The solid state ensembles were LiNbO$_3$ waveguides doped with Erbium ions absorbing at 1.53 $\mu$m. Bright coherent states of light in several temporal modes (up to 3) are stored and retrieved from the optical memories using two-pulse photon echoes. The stored and retrieved optical pulses, when combined at a beam splitter, show almost perfect interference, which demonstrates both phase preserving storage and indistinguishability of photon echoes from separate optical memories. By measuring interference fringes for different storage times, we also show explicitly that the visibility is not limited by atomic decoherence. These results are relevant for novel quantum repeaters architectures with photon echo based multimode quantum memories

Interference of Spontaneous Emission of Light from two Solid-State Atomic Ensembles

We report an interference experiment of spontaneous emission of light from two distant solid-state ensembles of atoms that are coherently excited by a short laser pulse. The ensembles are Erbium ions doped into two LiNbO3 crystals with channel waveguides, which are placed in the two arms of a Mach-Zehnder interferometer. The light that is spontaneously emitted after the excitation pulse shows first-order interference. By a strong collective enhancement of the emission, the atoms behave as ideal two-level quantum systems and no which-path information is left in the atomic ensembles after emission of a photon. This results in a high fringe visibility of 95%, which implies that the observed spontaneous emission is highly coherent

Results of a search for 2β\beta-decay of 136^{136}Xe with high-pressure copper proportional counters in Baksan Neutrino Observatory

The experiment for the 2$\beta$-decay of $^{136}$Xe search with two high-pressure copper proportional counters has been held in Baksan neutrino observatory. The search for the process is based on comparison of spectra measured with natural and enriched xenon. No evidence has been found for 2$\beta$(2$\nu$)- and 2$\beta$(0$\nu$)-decay. The decay half lifetime limit based on data measured during 8000 h is T$_{1/2}$$\geq8.5\cdot10^{21}$yr for 2$\nu$-mode and T$_{1/2}$$\geq3.1\cdot10^{23}$yr for 0$\nu$-mode (90%C.L.).Comment: 9 pages, 8 figures; talk at the NANP'05 Conference; submitted to Phys. At. Nuc

The Hilbert basis method for D-flat directions and the superpotential

We discuss, using the Hilbert basis method, how to efficiently construct a complete basis for D-flat directions in supersymmetric Abelian and non-Abelian gauge theories. We extend the method to discrete (R and non-R) symmetries. This facilitates the construction of a basis of all superpotential terms in a theory with given symmetries.Comment: 11 pages; a related mathematica code can be found at http://einrichtungen.ph.tum.de/T30e/codes/NonAbelianHilbert

Origin of atomic clusters during ion sputtering

Previous studies have shown that the size distributions of small clusters ( n<=40 n = number of atoms/cluster) generated by sputtering obey an inverse power law with an exponent between -8 and -4. Here we report electron microscopy studies of the size distributions of larger clusters ( n>=500) sputtered by high-energy ion impacts. These new measurements also yield an inverse power law, but one with an exponent of -2 and one independent of sputtering yield, indicating that the large clusters are produced when shock waves, generated by subsurface displacement cascades, ablate the surface