11 research outputs found
Observing the Onset of Effective Mass
The response of a particle in a periodic potential to an applied force is
commonly described by an effective mass which accounts for the detailed
interaction between the particle and the surrounding potential. Using a
Bose-Einstein condensate of 87-Rb atoms initially in the ground band of an
optical lattice, we experimentally show that the initial response of a particle
to an applied force is in fact characterized by the bare mass. Subsequently,
the particle response undergoes rapid oscillations and only over timescales
long compared to that of the interband dynamics is the effective mass observed
to be an appropriate description
Tunneling Dynamics of a Bose-Einstein Condensate
The simplicity and versatility of ultra-cold atoms make it an ideal system
for studying Quantum Mechanical phenomenon like tunneling.
This thesis describes progress towards experimentally
measuring the time spent by a tunneling particle in the classically forbidden region.
A detailed analysis of the experimental requirements to measure the tunneling
time is presented along with the experimental tools developed to meet
these requirements. These include a thin \SI{1.3}{\micro m}
optical tunnel barrier, a smooth atomic waveguide, and a Larmor clock
to measure the tunneling time. Delta-kick cooling is used to achieve the
extremely low temperatures required for the tunneling time experiments.
A 2.4x reduction in the atomic velocity spread is
demonstrated, reducing the rms velocity spread
to \SI{0.46(5)}{mm/s}. This corresponds to cooling to an effective
temperature of \SI{2.0(4)}{nK}.
The thin optical barrier opens up the possibility to study the decay of
quasi-bound condensates via tunneling. We develop a novel trapping
configuration for this purpose, in which the barrier acts as one of the
walls of the trap. Inter-atomic interactions strongly dictate
the escape dynamics of the condensate out of this trap, giving rise
to three distinct regimes--- classical over the barrier spilling, quantum
tunneling driven by interactions, and decay dominated by background losses.
We show that in the tunneling regime, the decay rate depends exponentially
with the chemical potential of the condensate. Experimental results show good
agreement with numerical solutions of the 3D Gross-Pitaevskii equation.Ph.D