Speaker: Ruben Cohen, Laboratoire Aimé Cotton, Orsay, France

Title: Thermalization in a 1D Rydberg gas: validity of the microcanonical ensemble hypothesis

Time and place: Monday 14 December in 1520-732 (coffee/tea and cake from 15:00)

Abstract:

We question the microcanonical hypothesis, often made to account for the thermalization of complex closed quantum systems, on the specific example of a chain of two-level atoms optically driven by a resonant laser beam and strongly interacting via Rydberg-Rydberg dipole-dipole interactions. Along its (necessarily unitary) evolution, this system is indeed expected to thermalize, i.e. observables, such as the number of excitations, stop oscillating and reach equilibrium-like expectation values. The latter are often calculated through assuming the system can be effectively described by a thermal-like microcanonical state. Here, we compare the distribution of excitations in the chain calculated either according to the microcanonical assumption or through direct exact numerical simulation. This allows us to show the limitations of the thermal equilibrium hypothesis and precise its applicability conditions.