# Berlin 2008 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 31: Quantum dynamics, decoherence and quantum information

### DY 31.6: Vortrag

### Freitag, 29. Februar 2008, 11:30–11:45, MA 004

**Dephasing and the steady state in quantum many-particle systems** — •Thomas Barthel and Ulrich Schollwöck — Institute for Theoretical Physics C, RWTH Aachen, D-52056 Aachen, Germany

We discuss relaxation in bosonic and fermionic many-particle systems. For integrable systems, the time-evolution from an arbitrary initial state can lead, for a given finite subsystem, to a definite steady state, determined by a certain maximum entropy density matrix. We give an explicit derivation of the steady state ensemble and devise sufficient prerequisites for the dephasing to take place. It is essential to restrict observations to a finite subsystem embedded into an (infinite) environment. We also find surprisingly simple scenarios, in which dephasing is ineffective and discuss the dependence on dimensionality and criticality. It also follows that, after a quench of system parameters, entanglement entropy will become extensive. It is thus simple to create strong entanglement for quantum computation applications, but in reduced Hilbert space simulations on classical computers, as MPS, PEPS or MERA algorithms, not possible to access arbitrarily long time scales.