Superfluid-Mott Insulator Transition of Spin-1 Bosons in an Optical Lattice

We have studied superfluid-Mott insulating transition of spin-1 bosons interacting antiferromagnetically in an optical lattice. We have obtained the zero-temperature phase diagram by a mean-field approximation and have found that the superfluid phase is to be a polar state as a usual trapped spin-1 Bose gas. More interestingly, we have found that the Mott-insulating phase is strongly stabilized only when the number of atoms per site is even.Comment: 9 pages, 1 figur

Bose-Einstein condensation at constant temperature

We present a novel experimental approach to Bose-Einstein condensation by increasing the particle number of the system at almost constant temperature. In particular the emergence of a new condensate is observed in multi-component F=1 spinor condensates of 87-Rb. Furthermore we develop a simple rate-equation model for multi-component BEC thermodynamics at finite temperature which well reproduces the measured effects.Comment: 4 pages, 3 figures, RevTe

Ultra-precise measurement of optical frequency ratios

We developed a novel technique for frequency measurement and synthesis, based on the operation of a femtosecond comb generator as transfer oscillator. The technique can be used to measure frequency ratios of any optical signals throughout the visible and near-infrared part of the spectrum. Relative uncertainties of $10^{-18}$ for averaging times of 100 s are possible. Using a Nd:YAG laser in combination with a nonlinear crystal we measured the frequency ratio of the second harmonic $\nu_{SH}$ at 532 nm to the fundamental $\nu_0$ at 1064 nm, $\nu_{SH}/\nu_0 = 2.000 000 000 000 000 001 \times (1 \pm 7 \times 10^{-19})$.Comment: 4 pages, 4 figure

Static properties and spin dynamics of the ferromagnetic spin-1 Bose gas in magnetic field

Properties of spin-1 Bose gases with ferromagnetic interaction in the presence of a nonzero magnetic field are studied. The equation of state and thermodynamic quantities are worked out with the help of a mean-field approximation. The phase diagram besides Bose-Einstein condensation contains a first order transition where two values of the magnetization coexist. The dynamics is investigated with the help of the Random Phase Approximation. The soft mode corresponding to the critical point of the magnetic phase transition is found to behave like in conventional theory.Comment: 8 pages and 3 figures included in text, submitted to Physical Review

Vortex structure in spinor F=2 Bose-Einstein condensates

Extended Gross-Pitaevskii equations for the rotating F=2 condensate in a harmonic trap are solved both numerically and variationally using trial functions for each component of the wave function. Axially-symmetric vortex solutions are analyzed and energies of polar and cyclic states are calculated. The equilibrium transitions between different phases with changing of the magnetization are studied. We show that at high magnetization the ground state of the system is determined by interaction in "density" channel, and at low magnetization spin interactions play a dominant role. Although there are five hyperfine states, all the particles are always condensed in one, two or three states. Two novel types of vortex structures are also discussed.Comment: 6 pages, 3 figure

A laser-driven target of high-density nuclear polarized hydrogen gas

We report the best figure-of-merit achieved for an internal nuclear polarized hydrogen gas target and a Monte Carlo simulation of spin-exchange optical pumping. The dimensions of the apparatus were optimized using the simulation and the experimental results were in good agreement with the simulation. The best result achieved for this target was 50.5% polarization with 58.2% degree of dissociation of the sample beam exiting the storage cell at a hydrogen flow rate of $1.1\times 10^{18}$ atoms/s.Comment: Accepted as a Rapid Communication article in Phys. Rev.

Momentum interferences of a freely expanding Bose-Einstein condensate in 1D due to interatomic interaction change

A Bose-Einstein condensate may be prepared in a highly elongated harmonic trap with negligible interatomic interactions using a Feshbach resonance. If a strong repulsive interatomic interaction is switched on and the axial trap is removed to let the condensate evolve freely in the axial direction, a time dependent quantum interference pattern takes place in the short time (Thomas-Fermi) regime, in which the number of peaks of the momentum distribution increases one by one, whereas the spatial density barely changes.Comment: 4 pages, 5 figure