Regensburg 2004 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 10: FV-internes Symposium ”Quantum Phase Transitions”

TT 10.4: Hauptvortrag

Dienstag, 9. März 2004, 11:50–12:25, H18

Monte Carlo simulations of quantum phase transitions in dissipative systems and ultra-cold atoms — •Matthias Troyer^1,2, Philipp Werner¹, Klaus Völker³, Fabien Alet^1,2, Stefan Wessel¹, and George G. Batrouni⁴ — ¹Theoretische Physik, ETH zürich — ²Computational Laboratory, ETH Zürich — ³University of Toronto — ⁴Université de Nice

The past decade has seen tremendous progress in quantum Monte Carlo algorithms. Advanced classical simulation techniques have been generalized to quantum system and further refined. This enables simulations with an unprecedented accuracy, allowing precise investigations of quantum phase transitions. Here we will focus on some recent results. The first part of the talk will be about the effect of dissipation on quantum phase transitions. While in classical simulations dynamics and thermodynamics are decoupled and dissipation thus has no influence on the universality class, the dynamics and thermodynamics are intrinsically coupled in a quantum system and can change the nature of the phase transition. We will present recent results on the phase diagrams and the critical behavior of dissipative quantum Ising models in a transverse field and preliminary results on quantum XY models. The second part of the talk will be on effects of constrained geometries, as they are created by an optical or magnetic trap on an ultra-cold atomic gas. We will demonstrate, that, the constrained geometry and the inhomogeneity of the trap lead to an absence of quantum critical behavior at the quantum phase transition in these systems. This explains the absence of critical slowing down in recent experiments,