Synopsis: Shaking atoms to make them stop

Ultracold atoms in an optical lattice share a lot of physics with electrons in a crystalline solid and it is a system that is often much easier to control. By forcing an optical lattice to vary with time, it is possible to engineer the energy of cold atoms and essentially bring them to a halt.
Synopsis figure
Illustration: Courtesy of Martin Holthaus

The spreading of a wave packet of cold atoms in an optical lattice is described by Bloch waves, similar to electrons in a crystalline lattice. Cold atoms in optical lattices can therefore mimic the physics of solids and they are often more manageable: the lattice is clean, tunable, and can be manipulated almost at will. For instance, one can apply a driving force that shifts the optical lattice periodically in time. Similar to a lattice that is periodic in space giving rise to a quasimomentum, a lattice that is periodic in time also introduces a quasienergy.

Writing in Physical Review A, a team of experimentalists and theoreticians from the ICFO in Barcelona, Spain, the Carl von Ossietzky Universität in Oldenburg, Germany, and the Università di Pisa in Italy show that a Bose-Einstein condensate of 87Rb atoms in a shaken optical lattice gives access to a new form of quantum state engineering. The group shows they can modify the Bloch bands of the atoms in a controllable way. For a particular choice of frequency and strength of the driving force, they can make the Bloch bands completely flat, which is equivalent to making the effective mass of the atoms infinite. In this way, they can suppress the tunneling of atoms in the lattice. This represents a nice realization of “dynamical localization,” which can be viewed as the quantum analog of the classical inverted pendulum stabilized by a force that is periodic in time.

Based on the good agreement between theory and experiment and in view of the large tunability of the key parameters, the idea of quasienergy band engineering appears to be a promising tool to realize band structures that might not have an analog in traditional solid-state physics. – Franco Dalfovo


Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Particles and Fields

String theory on the brane

Read More »

Next Synopsis

Particles and Fields

The narrowing search for the Higgs boson

Read More »

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