Non-equilibrium phase transitions with competing classical and quantum fluctuations

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• Matteo Marcuzzi (Nottingham)
• Wednesday 15 March 2017, 14:15-15:30
• Theory Library.

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Stochastic processes with absorbing states have been extensively studied in the past and are known to display, in the presence of suitable competing dynamical processes, non-equilibrium phase transitions. Recent works link the phytsics of these systems to the behaviour of cold atoms in optical lattices under the effect of strong dephasing noise. The question then arises on what happens when this noise is weak instead and how the characteristic non-equilibrium phase transitions of the classical case are transformed under the effect of quantum fluctuations. We have theoretically addressed such a scenario by studying an open quantum spin model which in its classical limit undergoes a directed percolation (continuous) phase transition. Via an approximate mapping to a non-equilibrium field theory, we have shown that the introduction of quantum fluctuations stemming from coherent, rather than stochastic, spin-flips alters the nature of the transition, which becomes first-order-like deep in the quantum regime. In-between these two limits, where classical and quantum dynamics compete on equal terms, a bicritical point is highlighted which lies in the so-called tricritical directed percolation class.

[1] Phys. Rev. B 95 , 014308 (2017) [2] Phys. Rev. Lett. 116, 245701 (2016)

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