We prepare mixtures of ultracold CaF molecules and Rb atoms in a magnetic trap and study their inelastic collisions. When the atoms are prepared in the spin-stretched state and the molecules in the spinstretched component of the first rotationally excited state, they collide inelastically with a rate coefficient k 2 ¼ ð6.6 AE 1.5Þ × 10 −11 cm 3 =s at temperatures near 100 μK. We attribute this to rotation-changing collisions. When the molecules are in the ground rotational state we see no inelastic loss and set an upper bound on the spin-relaxation rate coefficient of k 2 < 5.8 × 10 −12 cm 3 =s with 95% confidence. We compare these measurements to the results of a single-channel loss model based on quantum defect theory. The comparison suggests a short-range loss parameter close to unity for rotationally excited molecules, but below 0.04 for molecules in the rotational ground state.
We demonstrate the trapping of cold 87 Rb atoms in a toroidal geometry using a rf-dressed quadrupole magnetic trap formed by superposing a strong radio frequency (rf) field on a quadrupole trap. This rf-dressed quadrupole trap has minimum of the potential away from the quadrupole trap centre on a circular path which facilitates the trapping in the toroidal geometry. In the experiments, the laser cooled atoms were first trapped in the quadrupole trap, then cooled evaporatively using a weak rf-field, and finally trapped in the rf-dressed quadrupole trap. The radius of the toroid could be varied by varying the frequency of the dressing rf-field. It has also been demonstrated that a single rf source and an antenna can be used for the rf-evaporative cooling as well as for rf-dressing of atoms. The atoms trapped in the toroidal trap may have applications in realization of an atom gyroscope as well as in studying the quantum gases in low dimensions.
In this work, the RF-dressed potentials generated using a static magnetic
field of a quadrupole trap and various radio frequency (RF) fields, have been
theoretically investigated for trapping and manipulations of cold atoms in a
two-dimensional (2D) geometry. It is shown that, in this scheme, the RF fields
of some particular polarizations and phases can give rise to some novel static
and time-dependent anisotropic two-dimensional potentials which are useful to
trap and manipulate the cold atoms in the 2D geometry. The generated
time-dependent 2D potentials, rotating on the circular ring, can be used for
the controlled rotation and oscillation of the cold atom cloud on the circular
ring path. The ultracold atoms trapped in these potentials may be used to
investigate the interesting physics phenomena such as tunnelling and
super-fluidity.Comment: 21 Pages and 9 figure
The electromagnetically induced transparency (EIT) observations in two Λ-systems of 87 Rb atom, |5 2 S 1/2 F = 1 → |5 2 P 3/2 F = 1 ← |5 2 S 1/2 F = 2 and |5 2 S 1/2 F = 1 → |5 2 P 3/2 F = 2 ← |5 2 S 1/2 F = 2 , have been investigated in detail and the results are found consistent with our proposed theoretical models. The second Λ-system provides EIT signal with higher magnitude than the first system, both in absence and in presence of an applied magnetic field. The observed steeper slope of the EIT signal in presence of the magnetic field can enable one to achieve tight frequency locking of lasers using these EIT signals.
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