Atomic physics: Quantum theory verified by experiment.

Abstract

Systems of quantum objects can be characterized by the correlations between the objects. A technique that precisely measures even the most delicate of these correlations allows models of quantum systems to be tested. See Letter p.323 Ultracold gases of rubidium atoms on a quantum chip are well established analogue quantum simulators of quantum many-body physics. The system has been proposed to be described by a field theory called the sine-Gordon model, but verifying this requires direct measurement of higher-order correlation functions. Knowing all of the correlation functions of a system implies being able to characterize the system and solve the underlying quantum many-body problem. Here, the authors measure the higher-order correlation functions in an ultracold gas on a quantum chip from interference patterns, quantitatively confirming that it can indeed be described by a sine-Gordon model. Their methodology could in principle be applied to many types of quantum systems and hence will help to transform analogue quantum simulators into more quantitative and insightful tools.