Observation of dynamical many-body quantum phase transitions beyond Kibble-Zurek mechanism

The quantum critical behaviors of many-body phase transition is one of the most fascinating but also challenging questions in quantum physics. Here, we develop an improved band-mapping method, and investigate the dynamical quantum phase transition from a superfluid to a Mott insulator. We observe the quantum critical behaviors deviate from a universal power-law scaling description which is known as the Kibble-Zurek mechanism. There is an asymmetric quantum critical behavior around the critical point that there are a rapid response in the superfluid regime and a much retarded or even failed relaxation in the Mott insulator side. The response time and the excitation fraction in Mott insulators are dominated by two different power-law scaling which is inconsistent with the universality of quantum criticality. This shows that there may be complex mechanism competitions in many-body quantum phase transition which cannot be simply captured by the conventional Kibble-Zurek Mechanism.