Dartmouth Events

Horacio M. Pastawski

Instituto de Física Enrique Gaviola (IFEG) and Facultad de Matemática Astronomía y Física (FaMAF), Universidad Nacional de Córdoba

Title: "Spin dynamics with Solid State NMR and GPU Calculations: Loschmidt Echoes, Intrinsic Decoherence and Quantum Dynamical Phase Transitions."

Abstract: I will focus on the Loschmidt Echo [LE], a concept developed and pursed at Córdoba. It is the recovered fraction of  a localized excitation after a spreading period followed by an imperfect time reversal procedure [1]. In Solid State NMR, the LE has allowed us to quantify the decoherence and irreversibility induced by an uncontrolled environment. Notably complex many-body dynamics makes the system particularly sensitive to environmental disturbances presenting a decoherence rate that becomes perturbation independent beyond some small threshold. These experiments and the theoretical analysis based on the Feynman's path integral,  summarized at a tutorial level, fueled the field of dynamical quantum chaos. The quest for a perturbation independent decoherence as an emergent phenomenon in thermodynamic limit, lead us to  discuss other dynamical observables that depend non-analytically on the environment strength, i.e. that undergo a quantum dynamical phase transition QDPT [2]. GPU based high performance computing boosts the evaluation of the LE [3], allowing us to asses thermalization and how the Metal-Insulator transition (also a QDPT) emerges in interacting many-body systems.

[1] Loschmidt Echo A. Gousev, R.A. Jalabert, HMP and D.A. Wisniacki. Scholarpedia 7, 11687 (2012)  http://www.scholarpedia.org/article/Loschmidt_echo

[2] Environmentally induced quantum dynamical phase transition in the spin swap operation, G.A.Álvarez, E.P.Danieli, P.R. Levstein, and HMP, J. Chem.Phys. 124, 1 (2006)

[3] Interaction-disorder competition in a spin system evaluated through the Loschmidt echo P.R. Zangara, A.D. Dente, A. Iucci, P.R. Levstein, and HMP, Phys. Rev. B 88, 195106 (2013)