Free fermion antibunching in a degenerate atomic Fermi gas released from an optical lattice

Noise in a quantum system is fundamentally governed by the statistics and the many-body state of the underlying particles1,2,3,4. The correlated noise5,6,7 observed for bosonic particles (for example, photons8 or bosonic neutral atoms9,10,11,12,13,14) can be explained within a classical field description with fluctuating phases; however, the anticorrelations (‘antibunching’) observed in the detection of fermionic particles have no classical analogue. Observations of such fermionic antibunching are scarce and have been confined to electrons15,16,17 and neutrons18. Here we report the direct observation of antibunching of neutral fermionic atoms. By analysing the atomic shot noise3,10,19 in a set of standard absorption images of a gas of fermionic 40K atoms released from an optical lattice, we find reduced correlations for distances related to the original spacing of the trapped atoms. The detection of such quantum statistical correlations has allowed us to characterize the ordering and temperature of the Fermi gas in the lattice. Moreover, our findings are an important step towards revealing fundamental fermionic many-body quantum phases in periodic potentials, which are at the focus of current research.