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We analyze the atomic dynamics in an ac driven periodic optical potential which is symmetric in both time and space. We experimentally demonstrate that in the presence of dissipation the symmetry is broken, and a current of atoms through the optical lattice is generated as a result.
We investigate experimentally the route to quasiperiodicity in a driven ratchet for cold atoms and examine the relationship between symmetries and transport while approaching the quasiperiodic limit. Depending on the specific form of driving, quasiperiodicity results in the complete suppression of transport, or in the restoration of the symmetries which… (More)
We demonstrate experimentally a gating ratchet with cold rubidium atoms in a driven near-resonant optical lattice. A single-harmonic periodic modulation of the optical potential depth is applied, together with a single-harmonic rocking force. Directed motion is observed as a result of the breaking of the symmetries of the system.
We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this… (More)
We demonstrate the phenomenon of resonant activation in a nonadiabatically driven dissipative optical lattice with broken time symmetry. The resonant activation results in a resonance as a function of the driving frequency in the current of atoms through the periodic potential. We demonstrate that the resonance is produced by the interplay between… (More)
Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves… (More)
Overview Most of our results in the past year reflect our focus on strongly interacting quantum gases. The highlight has been the study of fermionic superfluidity with variable interactions and population imbalance. A non-interacting zero-temperature Bose-Einstein condensate is the matter-wave analogue to the optical laser, and therefore the ideal atom… (More)
Ultracold neutral Fermi gases provide a novel platform for the experimental quantum simulation of correlated many-body systems. The study of fluctuations and correlations in Fermi gases and the development of appropriate measurement methods are the subject of this thesis. Spatial atom noise analysis performed for expanded clouds of an ideal Fermi gas… (More)
Overview All our results in the past year reflect our focus on strongly interacting quantum gases. Although we published only two papers, both were major accomplishments. The superfluid gap is the most important parameter characterizing the superfluid state, and we were able to observe it for the first time. Our experiment on ferromagnetism is the first… (More)
Sometimes experimental noise is actually signal. Two groups have shown how density fluctuations in a gas of identical fermions can be used as a nanokelvin thermometer. Suppose you have a large volume of an ordinary gas and you examined a small subvolume within it that contains a mean number of particles N. You would expect that the variance of that number,… (More)