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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

Thursday, 25 October 2007
(at 16:30 in room 115, Hallwachsstr. 3)
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Revisiting the Fermi golden rule: quantum dynamical phase transition as a paradigm shift

Horacio Pastawski

Universidad Nacional de Cordoba

Since ancient times, phase transitions have nurtured both technological and scientific progress, but only in the last century has it become clear that phase transitions occur when the relevant free energy is non-analytic on some controlled thermodynamic variables such as the temperature. However, it has been a great challenge to show how this collective behavior emerges from the fundamental interactions governing microscopic variables. As occurs with the Fermi Golden Rule [1], one condition to obtain the discontinuous behavior is the proper evaluation of a classical or quantum thermodynamic limit: the number of degrees of freedom and a time scale go to infinity in a sequential order. We show that in presence of an environment, the oscillatory dynamics of a quantum two-level system, in analogy with a classical damped oscillator, can undergo a quantum dynamical phase transition to a non-oscillatory phase [2]. This is obtained from a very simple form of a self-consistent (Dyson) equation that describes the evolution of a density excitation [3]. I argue that each side of the transition implies different paradigms.
According to its characteristics, an oscillator can be in Aristotle's ideal universe, where friction is the dominant effect, or in a world ruled by Newton's laws, where the inertia is the dominant concept and friction is a correction. In consequence, paradigm incommensurability, as defined by Thomas Kuhn, obtains a sound mathematical justification as a consequence of the non-analyticity of the observables. Under this perspective one can understand other classical polemics in physics, as that between Boltzmann and Poincare/Zermelo or that between Boltzmann and Loschmidt. A strong case is made on the need to deepen the public's intuition and understanding on the abrupt transition from static to dynamical friction regimes [4].
[1] Non-Markovian decay beyond the Fermi Golden Rule: Survival Collapse of the polarization in spin chains. E. Rufeil Fiori and H. M. Pastawski Chem.Phys.Lett., 420, 35-41 (2006)
[2] Environmentally induced quantum dynamical phase transition in the spin swapping operation G. A. ülvarez, E. P. Danieli, P. R. Levstein, and H. M. Pastawski J. Chem. Phys. 124, 1 (2006)
[3] Quantum dynamical phase transition in a system with many-body interactions E. P. Danieli, G. A. ülvarez, P. R. Levstein and H. M. Pastawski Sol. St. Comm. 141, 422 (2007)
[4] Revisiting the Fermi Golden Rule: Quantum dynamical phase transition as a paradigm shift H. M. Pastawski Phys. B 398 278 (2007)

Brief Bio:

Prof. Horacio Pastawski completed his PhD in 1986 at Instituto Balseiro, San Carlos de Bariloche (Argentina), with Prof. Arturo Lopez-Davalos. His PhD thesis was on localization effects in disordered systems. During the period 1987-1988 he was a postdoctoral fellow at the Centre for Technological Research at Santa Fe (Argentina). Between 1989 and 1992, he was a visiting scientist at the Massachusetts Institute of Technology (group of Prof. Patrick Lee). Since then, he works at the University of Cordoba (Argentina). He is now a Principal Researcher of CONICET (Argentina's most prestigious research institution) and leads an experimental team on Nuclear Magnetic Resonance (LaNAIS). He is also a Senior Associate at the Abdus Salam International Centre for Theoretical Physics, Trieste (Italy). Prof. Pastawski is the author of more than 60 scientific papers, including highly influential contributions to the areas of quantum transport, spin-dynamics and the quantum-classical transition. His works have attracted the attention of prominent scientists such as Richard R. Ernst (Nobel Prize of Chemistry 1991) and Wojciech Zurek.

Invited by G. Cuniberti and L. Foa Torres (nanoSeminar)

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