Quantum Phase Transition from a Superfluid to a Mott Insulator in an Ultracold Gas of Atoms
M. Greiner
Max-Planck-Institut fur Quantenoptik Hans-Kopfermann-Str. 1 D-85748 Garching Germany
A quantum phase transition occurs when atoms from a Bose-Einstein condensate are loaded into a three dimensional optical lattice potential. For low potential depths the atoms are superfluid and delocalized over the entire lattice. For high potential depths the repulsive interactions between the atoms cause a transition to a Mott insulator phase. In this phase the atoms are localized to lattice sites with an exactly defined atom number per site. In recent experiments we have also been able to observe that ultracold collisions between atoms lead to a collapse, but then to a revival of the macroscopic wave function. The experiments directly demonstrate the quantisation of the matter wave field of a Bose-Einstein condensate. A new field of physics with ultracold atoms is entered.
A Bose-Einstein Condensate immersed in a Fermi Sea: observation of the simultaneous degeneracy in dilute atomic gases of 6Li/7Li
Lev Khaykovich
Laboratoire Kastler Brossel, Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris CEDEX 5, France
We report the formation of a mixture of bosonic and fermionic quantum systems in a dilute atomic gas. Two isotopes of lithium atoms are pre-cooled by the standard laser cooling technique and transferred into a magnetic trap. Then the evaporation cooling is performed selectively on the bosonic isotope (7Li), while its fermionic contrepart (6Li) is cooled sympathetically until the simultaneous quantum degeneracy is reached. 7Li Bose-Einstein condensate contains very small fraction of thermal atoms and is in thermal equillibrium with 6Li Fermi sea at the temperature of 1/5 of the Fermi temperature.
Continuous Vortices and Collective Excitations in Ferromagnetic Spinor Bose-Einstein Condenstates
Takeshi Mizushimaa, Kazushige Machidaa, Takafumi Kitab
aDepartment of Physics, Okayama University, Okayama 700-8530, Japan
bDivision of Physics, Hokkaido University, Sapporo 060-0810, Japan
Bose-Einstein condensates (BEC) realized in alkali atomic gases with the hyperfine state F=1 keep ßpin" states degenerate and active under an optical trap. These systems, so-called spinor BEC are analogous to the A-phase of the superfluid 3He. Among various topological structures, the Mermin-Ho and Anderson-Toulouse vortices are proposed in superfluid 3He-A phase. These are continuous defects and non-singular l-vector texture. We demonstrate by solving the extended Gross-Pitaevskii equation that these topological structures are thermodynamically stable in ferromagnetic spinor BEC under rotation. Furthermore, we show the collective modes for the various kinds of the vortices within Bogoliubov theory.
Electron-spin resonance in quantum degenerate 2D atomic hydrogen gas
Sergey Vasilyeva, Jarno Järvinena, Alexandr Safonovb, Simo Jaakkolaa
aDepartment of Physics, University of Turku, FIN-20014 Turku, Finland
bISSSP, RRC Kurchatov Institute, 123182 Moscow, Russia
We report on experiments where two-dimensional Bose gas of atomic hydrogen has been compressed thermally on the surface of a miniature cold spot covered with superfluid helium 4He at temperatures below 100 mK. The maximum achieved surface densities, up to s » 5×1012 cm2, are well inside the quantum degeneracy regime with sL2 » 2. Detection of the adsorbed H¯ atoms in situ by ESR yields direct information on the surface density and temperature profiles over the cold spot and on the mean dipolar field and interatomic interactions in the 2D gas. The latter are influenced by the onset of local coherence and 2D superfluidity.