Synopsis: Boosting interactions in BECs

Tuning the interactions between ultracold atoms leads to a strongly interacting superfluid with properties more akin to liquid helium than a dilute Bose-Einstein condensate.
Synopsis figure

In the mid-1990s, researchers cooled atomic vapors to temperatures low enough to form a dilute Bose-Einstein condensate (BEC) where the atoms would all lock together in a single ground state. Another famous superfluid discovered earlier—low-temperature liquid helium—is a Bose condensate with much stronger interactions. Now researchers at JILA and the University of British Columbia have been able to tune the atom-atom scattering length in a rubidium BEC to a strongly interacting regime reminiscent of liquid helium.

To adjust the interactions between rubidium-85 atoms, the team used a mechanism called a Feshbach resonance in which colliding atoms strongly interact if their kinetic energy is equal to the energy of a bound state involving both atoms. This resonance can be tuned with an applied magnetic field, resulting in an adjustable scattering length. To measure the spectrum of excitations in the BEC, the researchers use Bragg spectroscopy: two counter-propagating lasers form an interference pattern that acts essentially as a moving diffraction grating. Rubidium atoms are scattered off the grating with momentum transfer determined by the period of the grating. Images of the BEC yield the momentum transfer as a function of excitation energy and the results showed substantial deviations from the case of a dilute weakly interacting BEC.

The strongly interacting BEC is interesting from a theoretical standpoint, and the Bragg interference technique provides a useful means of monitoring how transferring energy and momentum into such a system determines its excitations. – David Voss


Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Next Synopsis

Related Articles

Synopsis: Losing Light in a BEC
Atomic and Molecular Physics

Synopsis: Losing Light in a BEC

The index of refraction in a gas of bosons is enhanced relative to its value in a classical gas, a predicted quantum effect that has now been observed in ultracold sodium atoms. Read More »

Focus: Atoms As Thermometers
Atomic and Molecular Physics

Focus: Atoms As Thermometers

A small number of atoms in repeated trials can accurately measure the temperature of an ultracold gas cloud—a step toward measuring temperature on the micrometer scale. Read More »

Synopsis: Bad Cavities for Precise Lasers
Optics

Synopsis: Bad Cavities for Precise Lasers

The frequency of a laser based on trapped ultracold atoms can be made insensitive to fluctuations in the laser cavity’s length. Read More »

More Articles