Quantum Institute: Visitor Schedule

The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121.
For more information, contact Diego Dalvit.

December 7, 2006
12:30 PM

Philippe Jacquod,
Associate Professor of Physics, University of Arizona

A Semiclassical Theory of Decoherence

Abstract

In the decades since its inception, quantum theory has been the most thoroughly tested scientific theory ever. All attempts to contradict quantum theory have failed - to the contrary, quantum predictinos have been confirmed by an enormous body of experiments of utmost significance in areas as diverse as nuclear, atomic, molecular, optical and condensed matter physics. Yet, the world surrounding us behaves classically most of the time, suggesting that, one way or another, classical physics emerges out of quantum mechanics. Today's solution of this paradox is based on the realization that an experimentally probed system is always coupled to external degrees of freedom. This coupling sometimes reduces and often totally destroys quantum interference effects - an occurrence usually referred to as "decoherence".

In this talk I will present a new trajectory-based semiclassical approach to decoherence. The approach is valid in the "pure dephasing limit" when classical trajectories of the system are not affected by the coupling to the environment. In this regime, decoherence can be treated for complex environments such as chaotic systems or even coupled chaotic systems, going beyond the standard brownian motion model of uncoupled harmonic oscillators. I will first rederive known results of the "conceptual approach to decoherence", focusing mostly on the purity of the reduced density matrix. Most of the attention will next be devoted to applying this theory to coherent transport in mesoscopic systems, where a theory for the disappearance of measurable effects such as weak localization, universal conductance fluctuations and Aharonov-Bohm conductance oscillations will be presented. The range of validity of the theory will finally be discussed.