Seminar
Tuesday, 13 April, 2010
Group seminar MPQ: Thermalization of one dimensional quantum systems
Tuesday, 13.04.2010 10 a.m. (s.t.) in Herbert-Walther-lecture room, MPQ Garching
Dr. Mari Carmen Banuls, Cirac's Group, MPQ
For a closed quantum system evolving out of equilibrium, thermalization means that local expectation values attain some stationary values, independent of the details of the initial state.
For integrable systems, for which local conserved quantities restrict the relaxation process, convergence to a non-thermal state has been predicted. For non-integrable models, instead, thermalization is in generally expected. But recent experimental results showing no thermalization even away from integrability have triggered a lot of theoretical interest to the problem.
Using a new numerical algorithms, we have studied the time evolution of an infinite spin chain interacting under a non-integrable Hamiltonian. Surprisingly, we have found that different regimes of thermalization are possible, depending on the initial state of the system. Some states thermalize "strongly", meaning that all local expectation values converge to the thermal values. Other states, instead, exhibit "weak" thermalization, a situation in which local expectation values do not relax, and the thermal values are only recovered after taking time average. Finally, there is a third group of states for which we do not observe any sort of thermalization, to the longest times we may simulate.