14 research outputs found
Collective enhancement and suppression in Bose-Einstein condensates
The coherent and collective nature of Bose-Einstein condensate can enhance or
suppress physical processes. Bosonic stimulation enhances scattering in already
occupied states which leads to atom amplification, and the suppression of
dissipation leads to superfluidity. In this paper, we review several
experiments where suppression and enhancement have been observed and discuss
the common roots of and differences between these phenomena.Comment: ICAP proceedings; 12 figure
Basic Atomic Physics
Contains reports on five research projects.National Science Foundation Grant PHY 96-024740National Science Foundation Grant PHY 92-21489U.S. Navy - Office of Naval Research Contract N00014-96-1-0484Joint Services Electronics Program Grant DAAHO4-95-1-0038National Science Foundation Grant PHY95-14795U.S. Army Research Office Contract DAAHO4-94-G-0170U.S. Army Research Office Contract DAAG55-97-1-0236U.S. Army Research Office Contract DAAH04-95-1-0533U.S. Navy - Office of Naval Research Contract N00014-96-1-0432National Science Foundation Contract PHY92-22768David and Lucile Packard Foundation Grant 96-5158National Science Foundation Grant PHY 95-01984U.S. Army Research OfficeU.S. Navy - Office of Naval Research Contract N00014-96-1-0485AASERT N00014-94-1-080
The Formation of Preferences in Two‐Level Games: An Analysis of India’s Domestic and Foreign Energy Policy
Colliding and Moving Bose-Einstein Condensates: Studies of superfluidity and optical tweezers for condensate transport
Thesis Supervisor: Wolfgang Ketterle
Title: John D. MacArthur Professor of PhysicsIn this thesis, two different sets of experiments are described. The first is an exploration of the microscopic superfluidity of dilute gaseous Bose- Einstein condensates. The second set
of experiments were performed using transported condensates in a new BEC apparatus.
Superfluidity was probed by moving impurities through a trapped condensate. The
impurities were created using an optical Raman transition, which transferred a small fraction of the atoms into an untrapped hyperfine state. A dramatic reduction in the collisions between the moving impurities and the condensate was observed when the velocity of the impurities was close to the speed of sound of the condensate. This reduction was attributed
to the superfluid properties of a BEC.
In addition, we observed an increase in the collisional density as the number of impurity atoms increased. This enhancement is an indication of bosonic stimulation by the occupied final states. This stimulation was observed both at small and large velocities relative to the speed of sound. A theoretical calculation of the effect of finite temperature indicated that collision rate should be enhanced at small velocities due to thermal excitations. However, in
the current experiments we were insensitive to this effect. Finally, the factor of two between the collisional rate between indistinguishable and distinguishable atoms was confirmed.
A new BEC apparatus that can transport condensates using optical tweezers was constructed.
Condensates containing 10-15 million sodium atoms were produced in 20 s using
conventional BEC production techniques. These condensates were then transferred into
an optical trap that was translated from the âproduction chamber’ into a separate vacuum chamber: the âscience chamber’. Typically, we transferred 2-3 million condensed atoms in less than 2 s. This transport technique avoids optical and mechanical constrainsts of conventional condensate experiments and allows for the possibility of novel experiments.
In the first experiments using transported BEC, we loaded condensed atoms from the
optical tweezers into both macroscopic and miniaturized magnetic traps. Using microfabricated wires on a silicon chip, we observed excitation-less propagation of a BEC in a magnetic waveguide. The condensates fragmented when brought very close to the wire surface indicating that imperfections in the fabrication process might limit future experiments.
Finally, we generated a continuous BEC source by periodically replenishing a condensate held in an optical reservoir trap using fresh condensates delivered using optical tweezers.
More than a million condensed atoms were always present in the continuous source, raising the possibility of realizing a truly continuous atom lase.National Science Foundation (NSF), the Office of Naval Research (ONR), the Army Research Office and the Joint Services Electronics Program (JSEP) of the Army Research Office (ARO), the National Aeronautics and Space Administration (NASA), the Packard Foudation, NSF Graduate Fellowship and a JSEP Graduate Fellowship
Colliding and Moving Bose-Einstein Condensates: Studies of superfluidity and optical tweezers for condensate transport
Thesis Supervisor: Wolfgang Ketterle
Title: John D. MacArthur Professor of PhysicsIn this thesis, two different sets of experiments are described. The first is an exploration of
the microscopic superfluidity of dilute gaseous Bose-Einstein condensates. The second set
of experiments were performed using transported condensates in a new BEC apparatus.
Superfluidity was probed by moving impurities through a trapped condensate. The
impurities were created using an optical Raman transition, which transferred a small fraction
of the atoms into an untrapped hyperfine state. A dramatic reduction in the collisions
between the moving impurities and the condensate was observed when the velocity of the
impurities was close to the speed of sound of the condensate. This reduction was attributed
to the superfluid properties of a BEC.
In addition, we observed an increase in the collisional density as the number of impurity
atoms increased. This enhancement is an indication of bosonic stimulation by the occupied
final states. This stimulation was observed both at small and large velocities relative to the
speed of sound. A theoretical calculation of the effect of finite temperature indicated that
collision rate should be enhanced at small velocities due to thermal excitations. However, in
the current experiments we were insensitive to this effect. Finally, the factor of two between
the collisional rate between indistinguishable and distinguishable atoms was confirmed.
A new BEC apparatus that can transport condensates using optical tweezers was constructed.
Condensates containing 10-15 million sodium atoms were produced in 20 s using
conventional BEC production techniques. These condensates were then transferred into
an optical trap that was translated from the âproduction chamber’ into a separate vacuum
chamber: the âscience chamber’. Typically, we transferred 2-3 million condensed atoms
in less than 2 s. This transport technique avoids optical and mechanical constrainsts of
conventional condensate experiments and allows for the possibility of novel experiments.
In the first experiments using transported BEC, we loaded condensed atoms from the
optical tweezers into both macroscopic and miniaturized magnetic traps. Using microfabricated
wires on a silicon chip, we observed excitation-less propagation of a BEC in a
magnetic waveguide. The condensates fragmented when brought very close to the wire surface
indicating that imperfections in the fabrication process might limit future experiments.
Finally, we generated a continuous BEC source by periodically replenishing a condensate
held in an optical reservoir trap using fresh condensates delivered using optical tweezers.
More than a million condensed atoms were always present in the continuous source, raising
the possibility of realizing a truly continuous atom laserNational Science Foundation (NSF), the Office of
Naval Research (ONR), the Army Research Office and the Joint Services Electronics Program
(JSEP) of the Army Research Office (ARO), the National Aeronautics and Space Administration (NASA), and the Packard Foudation.
The NSF Graduate Fellowship and a JSEP Graduate Fellowship
Construction and characterization of a Magneto-Optical Trap (MOT)
Thesis (B.S.)--University of Rochester. Dept. of Physics and Astronomy, 1997.A vapor-loaded cesium Magneto-Optical Trap was constructed with diode-lasers. The MOT was observed in a vacuum chamber fitted with magnetic coils in antiHelmholtz configuration. The diode laser was line-narrowed using a grating and was tuned with help of a saturation cell spectroscopy. The cesium MOT worked quite well, but it was not possible to obtain characterization data with it. A sodium MOT was characterized by studying the dependence of the trap loading parameters on the intensity of the trapping beams. The maximum number of atoms in a trap (Nmax) and the trap lifetime (tMOT) were determined for various intensities. The behavior of Nmax and tMOT followed the theoretical predictions, however, tMOT did not contain ultra-cold collision signature but only the collision signature between trapped atoms and the background vapor atoms. The cross-section for collisions between the trapped atoms and the background vapor was calculated to be 1.4xlO-13 cm2• This value is comparable to currently measured values