arXiv subjects

S. T. Thompson

Publications and source records attributed to S. T. Thompson.

5 recordsLinked to original sources

arXiv2005

Ultracold Molecule Production Via a Resonant Oscillating Magnetic Field

A novel atom-molecule conversion technique has been investigated. Ultracold 85Rb atoms sitting in a DC magnetic field near the 155G Feshbach resonance are associated by applying a small sinusoidal oscillation to the magnetic field. There is resonant atom to molecule conversion when the modulation frequency closely matches the molecular binding energy. We observe that the atom to molecule conversion efficiency depends strongly on the frequency, amplitude, and duration of the applied modulation and on the initial phase space density of the sample. This technique offers high conversion efficiencies without the necessity of crossing or closely approaching the Feshbach resonance and allows precise spectroscopic measurements.

cond-mat.other↗

arXiv2004

Production Efficiency of Ultracold Feshbach Molecules in Bosonic and Fermionic Systems

We investigate the production efficiency of ultracold molecules in bosonic $^{85}$Rb and fermionic $^{40}$K when the magnetic field is swept across a Feshbach resonance. For adiabatic sweeps of the magnetic field, the conversion efficiency of each species is solely determined by the phase space density of the atomic cloud, in contrast to a number of theoretical predictions. Our novel model for the adiabatic pairing process, developed from general physical principles, accurately predicts the conversion efficiency for {\it both} ultracold gases of bosons and of fermions. In the non-adiabatic regime our measurements of the $^{85}$Rb molecule conversion efficiency follow a Landau Zener model, with a conversion efficiency that is characterized by the density divided by the time derivative of the magnetic field.

cond-mat.stat-mech↗

arXiv2004

Spontaneous Dissociation of 85Rb Feshbach Molecules

The spontaneous dissociation of 85Rb dimers in the highest lying vibrational level has been observed in the vicinity of the Feshbach resonance which was used to produce them. The molecular lifetime shows a strong dependence on magnetic field, varying by three orders of magnitude between 155.5 G and 162.2 G. Our measurements are in good agreement with theoretical predictions in which molecular dissociation is driven by inelastic spin relaxation. Molecule lifetimes of tens of milliseconds can be achieved close to resonance.

cond-mat.other↗

arXiv2003

Very high precision bound state spectroscopy near a $^{85}$Rb Feshbach resonance

We precisely measured the binding energy of a molecular state near the Feshbach resonance in a $^{85}$Rb Bose-Einstein condensate (BEC). Rapid magnetic field pulses induced coherent atom-molecule oscillations in the BEC. We measured the oscillation frequency as a function of B-field and fit the data to a coupled-channels model. Our analysis constrained the Feshbach resonance position [155.041(18) G], width [10.71(2) G], and background scattering length [-443(3) a$_0$] and yielded new values for $v_{DS}$, $v_{DT}$, and $C_6$. These results improved our estimate for the stability condition of an attractive BEC. We also found evidence for a mean-field shift to the binding energy.

cond-mat.stat-mech↗

arXiv2002

Microscopic Dynamics in a Strongly Interacting Bose-Einstein Condensate

An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a carefully controlled magnetic field pulse in the vicinity of a Feshbach resonance. This pulse probed the strongly interacting regime for the condensate, with calculated values for the diluteness parameter (na^3) ranging from 0.01 to 0.5. The field pulse was observed to cause loss of atoms from the condensate on remarkably short time scales (>=10 microsec). The dependence of this loss on magnetic field pulse shape and amplitude was measured. For triangular pulses shorter than 1 ms, decreasing the pulse length actually increased the loss, until extremely short time scales (a few tens of microseconds) were reached. Such time scales and dependencies are very different from those expected in traditional condensate inelastic loss processes, suggesting the presence of new microscopic BEC physics.

cond-mat.stat-mech↗