arXiv subjects

Giuseppe Zonzo

Publications and source records attributed to Giuseppe Zonzo.

3 recordsLinked to original sources

arXiv2017

Geometric phase of quenched spin models

We consider a spin belonging to a many body system in a magnetically ordered phase, which initial state is a symmetry broken ground state. We assume that in this system a sudden quench of the Hamiltonian induces an evolution. We show that the long time behavior of the spin state, can be approximated by the one of an open two level system in which the evolution preserves all the symmetries of the Hamiltonian. Exploiting such a result we analyze the geometric phase associated with the evolution of the single spin state and we prove analytically that its long time behavior depends on the physical phase realized after the quench. When the system arrives in a paramagnetic phase, the geometric phase shows a periodic behavior that is absent in the case in which the system remains in the initial ordered phase. Such a difference also survives in finite size systems until boundary effects come into play. We also discuss the effects of a explicit violation of the parity symmetry of the Hamiltonian and possible applications to the problem of the entanglement thermalization.

quant-ph↗

arXiv2016

Quench of symmetry broken ground states

We analyze the problem of how different ground states associated to the same set of the Hamiltonian parameters evolve after a sudden quench. To realize our analysis we define a quantitative approach to the local distinguishability between different ground states of a magnetically ordered phase in terms of the trace distance between the reduced density matrices obtained projecting two ground states in the same subset. Before the quench, regardless the particular choice of the subset, any system in a magnetically ordered phase is characterized by ground states that are locally distinguishable. On the other hand, after the quench, the maximum of the distinguishability shows an exponential decay in time. Hence, in the limit of very large time, all the informations about the particular initial ground state are lost even if the systems are integrable. We prove our claims in the framework of the magnetically ordered phases that characterize both the $XY$ model and $N$-cluster Ising models. The fact that we find similar behavior in models within different classes of symmetry makes us confident about the generality of our results.

quant-ph↗

arXiv2016

Quantum coherence of Gaussian states

We introduce a geometric quantification of quantum coherence in single-mode Gaussian states and we investigate the behavior of distance measures as functions of different physical parameters. In the case of squeezed thermal states, we observe that re-quantization yields an effect of noise-enhanced quantum coherence for increasing thermal photon number.

quant-ph↗