Rubidium Experiment: Quantum Simulation

Ultracold atoms can be trapped in periodic optical potentials. The achieved systems, so called optical lattices, much resemble an artificial solid. In earlier work, we have investigated the band structure of optical lattices of variable inversion symmetry, as a step towards simulating the diversity of potentials that nature provides us in the system of electrons in natural crystals. In our setup, optical potentials for atoms can be generated by means of Fourier-synthesis. For a nearly sawtooth-like potential, we use the superposition of a usual standing wave lattice of spatial periodicity λ/2 with a novel multiphoton lattice of periodicity λ/4. In this way, a dissipationless quantum ratchet could be realised, where the rectification of quantum fluctuations leads to a directed atomic motion. Effectively, this demonstrates the operational principle of microscopic quantum motors, as a prototype of microscopic machinery in the quantum world.

In other work, collaborating with the theory group of A. Rosch, we have used an optical lattice with a spatially chirped amplitude to realize an edge state between two spatial regions of different topological order. Atoms confined in the topological edge state were directly observed in real-space with an optical microscope More recently, collaborating with the theory group of E. Solano and E. Rico, we have studied ultra-strong coupling of two mechanical modes in the quantum Rabi regime und the combined action of atoms being confined by a lattice and an optical dipole trapping potential. With this novel experimental scheme, a record high coupling of 6.5 times the field mode frequency was obtained, so that the coupling term dominates over all other energy scales.