Halil Cakir

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Due to experimental advances in the preparation and control of
ultra-cold atomic gases, there is a widespread interest in the behaviour
of quantum systems out of equilibrium. A common way to probe quantum
systems for non-equilibrium phenomena is given by sudden quenches. I
will present results concerning the dynamics of the longitudinal spin
correlation function after a sudden quench in the Transverse Field Ising
Chain. A distinguishing feature of this model is that it exhibits a
quantum critical point separating a ferromagnetic from a paramagnetic
phase. Furthermore, the system can be expressed as a fermionic harmonic
oscillator, which allows us to determine the longitudinal correlation
function after a sudden quench exactly by using Wick's theorem. In
particular, I will concentrate on the behaviour of the longitudinal
correlation function for quenches from an initially large external field
to the vicinity of the quantum critical point within the paramagnetic
phase. We conjectured a formula for the asymptotic behaviour in this
case and compared it to numerical calculations of the correlator. Based
on this conjectured formula, we found that the decay of the correlation
function is characterized by two correlation lengths and that the
correlation function attains its stationary values already at short
distances.

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University of Heidelberg
Seminar Room 0.03, ETP
Contact: Simon Trebst