431 research outputs found
Magnetic Trapping of Metastable Calcium Atoms
Metastable calcium atoms, produced in a magneto-optic trap (MOT) operating
within the singlet system, are continuously loaded into a magnetic trap formed
by the magnetic quadrupole field of the MOT. At MOT temperatures of 3 mK and
240 ms loading time we observe 1.1 x 10^8 magnetically trapped 3P2 atoms at
densities of 2.4 x 10^8 cm^-3 and temperatures of 0.61 mK. In a modified scheme
we first load a MOT for metastable atoms at a temperature of 0.18 mK and
subsequently release these atoms into the magnetic trap. In this case 240 ms of
loading yields 2.4 x 10^8 trapped 3P2 atoms at a peak density of 8.7 x 10^10
cm^-3 and a temperature of 0.13 mK. The temperature decrease observed in the
magnetic trap for both loading schemes can be explained only in part by trap
size effects.Comment: 4 figure
Unconventional superfluid order in the -band of a bipartite optical square lattice
We report on the first observation of bosons condensed into the energy minima
of an -band of a bipartite square optical lattice. Momentum spectra indicate
that a truly complex-valued staggered angular momentum superfluid order is
established. The corresponding wave function is composed of alternating local
-orbits and local -orbits residing in the deep
and shallow wells of the lattice, which are arranged as the black and white
areas of a checkerboard. A pattern of staggered vortical currents arises, which
breaks time reversal symmetry and the translational symmetry of the lattice
potential. We have measured the populations of higher order Bragg peaks in the
momentum spectra for varying relative depths of the shallow and deep lattice
wells and find remarkable agreement with band calculations.Comment: 4 pages, 3 figure
Continuous loading of S calcium atoms into an optical dipole trap
We demonstrate an efficient scheme for continuous trap loading based upon
spatially selective optical pumping. We discuss the case of S
calcium atoms in an optical dipole trap (ODT), however, similar strategies
should be applicable to a wide range of atomic species. Our starting point is a
reservoir of moderately cold (K) metastable
P-atoms prepared by means of a magneto-optic trap (triplet-MOT). A
focused 532 nm laser beam produces a strongly elongated optical potential for
S-atoms with up to 350 K well depth. A weak focused laser beam
at 430 nm, carefully superimposed upon the ODT beam, selectively pumps the
P-atoms inside the capture volume to the singlet state, where they
are confined by the ODT. The triplet-MOT perpetually refills the capture volume
with P-atoms thus providing a continuous stream of cold atoms into
the ODT at a rate of s. Limited by evaporation loss, in 200 ms we
typically load atoms with an initial radial temperature of 85
K. After terminating the loading we observe evaporation during 50 ms
leaving us with atoms at radial temperatures close to 40 K and a
peak phase space density of . We point out that a
comparable scheme could be employed to load a dipole trap with
P-atoms.Comment: 4 pages, 4 figure
Normal mode splitting and mechanical effects of an optical lattice in a ring cavity
A novel regime of atom-cavity physics is explored, arising when large atom
samples dispersively interact with high-finesse optical cavities. A stable far
detuned optical lattice of several million rubidium atoms is formed inside an
optical ring resonator by coupling equal amounts of laser light to each
propagation direction of a longitudinal cavity mode. An adjacent longitudinal
mode, detunedby about 3 GHz, is used to perform probe transmission spectroscopy
of the system. The atom-cavity coupling for the lattice beams and the probe is
dispersive and dissipation results only from the finite photon-storage time.
The observation of two well-resolved normal modes demonstrates the regime of
strong cooperative coupling. The details of the normal mode spectrum reveal
mechanical effects associated with the retroaction of the probe upon the
optical lattice.Comment: 4 pages, 3 figure
Collective Sideband Cooling in an Optical Ring Cavity
We propose a cavity based laser cooling and trapping scheme, providing tight
confinement and cooling to very low temperatures, without degradation at high
particle densities. A bidirectionally pumped ring cavity builds up a resonantly
enhanced optical standing wave which acts to confine polarizable particles in
deep potential wells. The particle localization yields a coupling of the
degenerate travelling wave modes via coherent photon redistribution. This
induces a splitting of the cavity resonances with a high frequency component,
that is tuned to the anti-Stokes Raman sideband of the particles oscillating in
the potential wells, yielding cooling due to excess anti-Stokes scattering.
Tight confinement in the optical lattice together with the prediction, that
more than 50% of the trapped particles can be cooled into the motional ground
state, promise high phase space densities.Comment: 4 pages, 1 figur
Echo in Optical Lattices: Stimulated Revival of Breathing Oscillations
We analyze a stimulated revival (echo) effect for the breathing modes of the
atomic oscillations in optical lattices. The effect arises from the dephasing
due to the weak anharmonicity being partly reversed in time by means of
additional parametric excitation of the optical lattice. The shape of the echo
response is obtained by numerically simulating the equation of motion for the
atoms with subsequent averaging over the thermal initial conditions. A
qualitative analysis of the phenomenon shows that the suggested echo mechanism
combines the features of both spin and phonon echoes.Comment: 13 pages, 3 figure
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