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


Features

More Features »

Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Next Synopsis

Related Articles

Focus: Atomic Impersonator
Optics

Focus: Atomic Impersonator

Calculations show that a carefully engineered laser pulse can induce an atom to emit light as if it were a different atom. Read More »

Viewpoint: Transportable Clocks Move with the Times
Optics

Viewpoint: Transportable Clocks Move with the Times

Transportable atomic clocks are now operating with fractional-frequency uncertainties below one part in 1016, opening up new applications. Read More »

Viewpoint: Trapped Ions Stopped Cold
Optics

Viewpoint: Trapped Ions Stopped Cold

A novel method for cooling trapped ions could boost the accuracy of atomic clocks. Read More »

More Articles