Institute of Laser Physics
Institute
of Laserphysics
of Laserphysics
This page:UHH > MIN > Department of Physics > Research > Institutes > Institute of Laser Physics > Research > Theory Group Ultra-cold atoms
Theory Group Ultra-cold atoms and solid state systems
Prof. Dr. Ludwig Mathey
We investigate the theory of ultracold atom and solid state systems, with particular emphasis on many-body effects. One of our primary research interest is many-body dynamics, such as dynamic phase transitions and dynamic control of many-body systems, as well as properties of superfluidity and superconductivity. Furthermore, we study the equilibrium phase diagrams of ultra-cold atoms, at both finite and zero temperature. Another objective is the advancement of the technology of ultra-cold atom systems, for example by investigating new cooling and detection methods.
Recent activities:
Time crystals in a shaken atom-cavity system
Jayson G. Cosme, Jim Skulte, Ludwig Mathey
We demonstrate the emergence of a time crystal of atoms in a high-finesse optical cavity driven by a phase-modulated transverse pump field, resulting in a shaken lattice. This shaken system exhibits macroscopic oscillations in the number of cavity photons and order parameters at noninteger multiples of the driving period, which signals the appearance of an incommensurate time crystal. The subharmonic oscillatory motion corresponds to dynamical switching between symmetry-broken states, which are nonequilibrium bond ordered density wave states. Employing a semiclassical phase-space representation for the driven-dissipative quantum dynamics, we confirm the rigidity and persistence of the time crystalline phase. We identify experimentally relevant parameter regimes for which the time crystal phase is long-lived, and map out the dynamical phase diagram. We compare and contrast the incommensurate time crystal with the commensurate Dicke time crystal in the amplitude-modulated case.
An ideal Josephson junction in an ultracold two-dimensional Fermi gas
Niclas Luick, Lennart Sobirey, Markus Bohlen, Vijay Pal Singh, Ludwig Mathey, Thomas Lompe, Henning Moritz
Two-dimensional structures are present in almost all known superconductors with high critical temperatures, but the role of the reduced dimensionality is still under debate. Recently, ultracold atoms have emerged as an ideal model system to study such strongly correlated 2D systems. Here, we report on the realisation of a Josephson junction in an ultracold 2D Fermi gas. We measure the frequency of Josephson oscillations as a function of the phase difference across the junction and find excellent agreement with the sinusoidal current phase relation of an ideal Josephson junction. Furthermore, we determine the critical current of our junction in the crossover from tightly bound molecules to weakly bound Cooper pairs. Our measurements clearly demonstrate phase coherence and provide strong evidence for superfluidity in a strongly interacting 2D Fermi gas.
