Observation of the Hanbury Brown–Twiss effect with ultracold molecules

Measuring the statistical correlations of individual quantum objects provides an excellent way to study complex quantum systems. Ultracold molecules represent a powerful platform for quantum simulation 1 and quantum computation 2 due to their rich and controllable internal degrees of freedom. However, the detection of correlations between single molecules in an ultracold gas has yet to be demonstrated. Here we observe the Hanbury Brown–Twiss effect—the emergence of bunching correlations of indistinguishable particles collected by separate detectors—in a gas of bosonic 23 Na 87 Rb Feshbach molecules, enabled by the realization of a molecular quantum gas microscope. We detect the characteristic bunching correlations in the density fluctuations of a two-dimensional molecular gas released from and subsequently recaptured in an optical lattice. The quantum gas microscope allows us to extract the positions of individual molecules with single-site resolution. As a result, we obtain a two-molecule interference pattern with high visibility. Although these measured correlations purely arise from the quantum statistics of the molecules, the demonstrated imaging capabilities open the way for site-resolved studies of interacting molecular gases in optical lattices. The study of statistical correlations is central to the description of complex quantum objects. Measurements of density correlation functions of ultracold molecules are now possible through the realization of a molecular quantum gas microscope.