Quantum simulation of Unruh radiation

The exploration of quantum phenomena in a curved spacetime is an emerging interdisciplinary area at the interface between general relativity(1-4), thermodynamics(4-6) and quantum information(7,8). One famous prediction in this field is Unruh thermal radiation(3)-the manifestation of thermal radiation from a Minkowski vacuum when viewed in an accelerating reference frame. Here, we report the experimental observation of a matter field with thermal fluctuations that agree with Unruh's predictions. The matter field is generated within a framework for the simulation of quantum physics in a non-inertial frame, based on Bose-Einstein condensates that are parametrically modulated(9) to make their evolution replicate the frame transformation. We further observe long-range phase coherence and temporal reversal of the matter-wave radiation, hallmarks that distinguish Unruh radiation from its classical counterpart. Our demonstration offers a new avenue for the investigation of the dynamics of quantum many-body systems in a curved spacetime.