Ultracold Bosons in Optical Superlattices
Experiments with ultracold bosons in optical superlattices
In our experiments with ultracold bosonic rubidium atoms in optical superlattices, we are studying quantum phases and phase transitions in specific condensed matter models as well as questions of quantum many-body dynamics (more). Every experimental run starts out with the creation of a Bose-Einstein condensate of Rb-78 using a magneto-optical trap (MOT) and forced evaporation in a magnetic trap and, later, in an optical dipole trap.
Beyond this initial step, our main tool is an optical superlattice formed by overlapping two standing-wave laser fields with a commensurate wavelength ratio of 2 (more). Two perpendicular optical lattices complete the setup of a regular three-dimensional lattice with a unit cell of two sites. Full dynamical control over the individual laser-beam intensities as well as over the relative phase between the two standing waves forming the superlattice allows us to set all relevant parameters of the atomic many-body system. We are currently extending this system by replacing one of the transverse lattice by another superlattice, thus obtaining a unit cell of four sites – a plaquette.
The future ...
With the extension to the two-axes superlattice, we aim at, for example, realizing minimal versions of topologically ordered quantum phases of bosons. Such phases with topological order cannot be classified by an order parameter and represent a new class of many-body systems without any local order. Only by carrying globals measurements on the system, one can reveal the hidden order in the system.
Furthermore, we will be able to create, control and detect spin-correlated states in two dimensions in analogy to 2D valence bond solid states, and to follow their dynamics. Such states are of general interest in the context of quantum magnetism and high-temperature superconductivity.
... the past
Some examples of experiments performed with the single superlattice potential – still in Mainz – include the direct observation of atom co-tunneling of repulsively interacting atoms, the observation and control of superexchange interactions between neighboring atoms and the controlled creation and detection of spin-correlations in the optical lattice. In terms of dynamics, we have investigated the relaxation of strongly correlated bosons in one-dimensional chains following a quantum quench. Another experiment dealt with many-body Landau-Zener sweeps with one-dimensional quantum gases and a drastic breakdown of adiabaticity far from equilibrium.
Even before the implementation of our first superlattice, the machine went through a long history of experiments with single-wavelength optical lattices. Prominent examples from the list of results are the observation of the quantum phase transition from a superfluid to a bosonic Mott insulator, the measurement of the collapse-and-revival dynamics of a matter-wave field and the realization of a Tonks-Girardeau gas. More recently, we could also demonstrate the storage of light in a Mott insulator by means of electrically induced transparency and determine a quantitative phase diagram of the Bose-Hubbard model at finite temperatures.