We study the full counting statistics (FCS) of quantum gases in samples of thousands of interacting bosons, detected atom by atom after a long free-fall expansion.In this far-field configuration, the FCS reveals the many-body coherence from which we characterize iconic states of interacting lattice bosons by deducing their normalized correlations g (n) (0) up to the order n = 6.In Mott insulators, we find a thermal FCS characterized by perfectly contrasted correlations g (n) (0) = n!.In interacting Bose superfluids, we observe small deviations to the Poisson FCS and to the ideal values g (n) (0) = 1 expected for a pure condensate.These deviations become larger as we increase the interaction strength and reveal the role of the quantum depletion of the condensate on many-body coherence.The approach to many-body correlations demonstrated here is readily extendable to characterize a large variety of interacting quantum states and phase transitions.
We study the full counting statistics (FCS) of quantum gases in samples of thousands of interacting bosons, detected atom-by-atom after a long free-fall expansion. In this far-field configuration, the FCS reveals the many-body coherence from which we characterize iconic states of interacting lattice bosons, by deducing the normalized correlations
g(n)(0) up to the order
n=6. In Mott insulators, we find a thermal FCS characterized by perfectly-contrasted correlations
g(n)(0)=n!. In interacting Bose superfluids, we observe small deviations to the Poisson FCS and to the ideal values
g(n)(0)=1 expected for a pure condensate. To describe these deviations, we introduce a heuristic model that includes an incoherent contribution attributed to the depletion of the condensate. The predictions of the model agree quantitatively with our measurements over a large range of interaction strengths, that includes the regime where the condensate is strongly depleted by interactions. These results suggest that the condensate component exhibits a full coherence
g(n)(0)=1 at any order
n up to
n=6 and at arbitrary interaction strengths. The approach demonstrated here is readily extendable to characterize a large variety of interacting quantum states and phase transitions.
We investigate density fluctuations in a coherent ensemble of interacting fermionic atoms around the BEC‐BCS crossover. Adapting the concept of full counting statistics, well‐known from quantum optics and mesoscopic electron transport, we study second‐order as well as higher‐order correlators of density fluctuations. This method is applied to the crossover from a molecular BEC state to a fermionic BCS state and yields a transition from Poissonian statistics to binomial statistics. The statistics can thus be used as an experimental tool to gain information on the many‐body ground state in the crossover regime.