A. Mosk

Sympathetic cooling with two atomic species in an optical trap

We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a CO2 laser and study the exchange of thermal energy between the gases. The optically cooled cesium gas efficiently decreases the temperature of the lithium gas through sympathetic cooling. Equilibrium temperatures down to 25 microK have been reached. The measured cross section for thermalizing 133Cs-7Li collisions is 8 x 10(-12) cm(2), for both species unpolarized in their lowest hyperfine ground state. Besides thermalization, we observe evaporation of lithium purely through elastic cesium-lithium collisions (sympathetic evaporation).

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

Abstract.We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO2 laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross-section for cold elastic Li-Cs collisions.

Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms

We study elastic collisions in an optically trapped spin mixture of fermionic lithium atoms in the presence of magnetic fields up to 1.5 kG by measuring evaporative loss. Our experiments confirm the expected magnetic tunability of the scattering length by showing the main features of elastic scattering according to recent calculations. We measure the zero crossing of the scattering length at 530(3) G which is associated with a predicted Feshbach resonance at approximately 850 G. Beyond the resonance we observe the expected large cross section in the triplet scattering regime.

Resonator-enhanced optical dipole trap for fermionic lithium atoms.

We demonstrate a novel optical dipole trap that is based on enhancement of the optical power density of a Nd:YAG laser beam in a resonator. The trap is particularly suited for experiments with ultracold gases, as it combines a potential depth of the order of 1 mK with storage times of several tens of seconds. We study the interactions in a gas of fermionic lithium atoms in our trap and observe the influence of spin-changing collisions and off-resonant photon scattering. A key element in reaching long storage times is the use of an ultralow-noise laser. The dependence of storage time on laser noise is investigated.

Trapping of Rb atoms by ac electric fields.

We demonstrate trapping of an ultracold gas of neutral atoms in a macroscopic ac electric trap. Three-dimensional confinement is obtained by switching between two saddle-point configurations of the electric field. Stable trapping is observed in a narrow range of switching frequencies around 60 Hz. The dynamic confinement of the atoms is directly visualized at different phases of the ac switching cycle. We observe about 10(5) Rb atoms in the 1 mm3 large and several microkelvins deep trap with a lifetime of approximately 5 s.

Low-cost mechanical shutter for light beams

We present a simple design of a fast mechanical shutter for light beams using a low-cost personal computer loudspeaker. The shutter is capable of closing an aperture of 5 mm at a maximum speed of 1.7 mm/ms with a timing jitter of less than 10 μs. When combined with polarization optics, our device can also be used as an alterable switch and adjustable attenuator.

Atomic deuterium adsorbed on the surface of liquid helium

We investigate deuterium atoms adsorbed on the surface of liquid helium in equilibrium with a vapor of atoms of the same species. These atoms are studied by a sensitive optical method based on spectroscopy at a wavelength of 122 nm, exciting the 1S-2P transition. We present a direct measurement of the adsorption energy of deuterium atoms on helium and show evidence for the existence of resonantly enhanced recombination of atoms residing on the surface to molecules.

Fermionic lithium atoms in a resonator dipole trap

Summary form only given. In a neutral Fermi gas the interplay between interatomic interactions and quantum statistics is fascinating. Interactions between particles in identical internal states become forbidden at low temperatures, while interactions between particles in non-identical spin states may be the driving mechanism for an expected phase transition to superfluidity. It is therefore interesting to study the interactions between fermionic atoms in different spin states.

Interactions of lithium and cesium in an optical dipole trap

The thermodynamics in a mixture of two different atomic gases at ultralow temperatures are explored. An intrinsically loss-free approach is presented which can be generalized to a vast range of atomic species and even molecules. The model system is a mixture of cesium and lithium in an extremely far-detuned optical dipole trap. Cesium is an excellent cooling agent, since it can be optically cooled to very low temperatures, mainly due to its high mass. Lithium, on the other side, is difficult to cool optically. In addition, it is nearly an ideal gas due the very small cross-section for elastic Li-Li collisions. Thermalization of Li thus occurs purely through collisions with the Cs atoms. From the time scale of thermalization one can deduce the a priori unknown interspecies scattering cross-section. Currently, the formation of ultracold Cs/sub 2/ molecules through photoassociation in the dipole trap is being investigated. The production of molecules in the lowest vibrational states of the outer well of the O/sub g//sup -/ potential is possible to observe by investigating the trap loss signals. Phenomena like saturation effects can be studied.

Feshbach-tuned Fermionic lithium gas

The effect of the magnetic field on the elastic scattering properties is studied by looking at thermalization of an initially non-thermal distribution in an optical dipole trap. While thermalizing, a significant number of atoms evaporates from the trap at a time scale determined by the scattering cross section. The remaining fraction of atoms is observed after 1 s and 3 s. The obtained result confirms the expectations with the most pronounced feature being a peak in the remaining fraction where the scattering length crosses zero.