scholarly journals Exceptional Points and Dynamical Phase Transitions

10.14311/1273 ◽  
2010 ◽  
Vol 50 (5) ◽  
Author(s):  
I. Rotter
Keyword(s):  
Phase Transitions ◽  
Quantum Physics ◽  
Open Quantum Systems ◽  
Level Density ◽  
Experimental Studies ◽  
Quantum Systems ◽  
Microwave Cavity ◽  
Exceptional Points ◽  
Dynamical Phase ◽  
Dynamical Phase Transitions

In the framework of non-Hermitian quantum physics, the relation between exceptional points,dynamical phase transitions and the counter intuitive behavior of quantum systems at high level density is considered. The theoretical results obtained for open quantum systems and proven experimentally some years ago on a microwave cavity, may explain environmentally induce deffects (including dynamical phase transitions), which have been observed in various experimental studies. They also agree(qualitatively) with the experimental results reported recently in PT symmetric optical lattices.

scholarly journals Dynamical phase transitions and Loschmidt echo in the infinite-range XY model

2016 ◽  
Vol 374 (2069) ◽  
pp. 20150160 ◽  
Author(s):  
Bojan Žunkovič ◽  
Alessandro Silva ◽  
Michele Fabrizio
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Order Parameter ◽  
Quantum Systems ◽  
Xy Model ◽  
Time Behaviour ◽  
Dynamical Phase ◽  
Dynamical Phase Transitions ◽  
Loschmidt Echo ◽  
Infinite Range

We compare two different notions of dynamical phase transitions in closed quantum systems. The first is identified through the time-averaged value of the equilibrium-order parameter, whereas the second corresponds to non-analyticities in the time behaviour of the Loschmidt echo. By exactly solving the dynamics of the infinite-range XY model, we show that in this model non-analyticities of the Loschmidt echo are not connected to standard dynamical phase transitions and are not robust against quantum fluctuations. Furthermore, we show that the existence of either of the two dynamical transitions is not necessarily connected to the equilibrium quantum phase transition.

scholarly journals Loss, Gain, and Singular Points in Open Quantum Systems

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Hichem Eleuch ◽  
Ingrid Rotter
Keyword(s):  
Parameter Space ◽  
Critical Points ◽  
Quantum Physics ◽  
Open Quantum Systems ◽  
Quantum Systems ◽  
Experimental Results ◽  
Open Quantum ◽  
Exceptional Points ◽  
Complex Eigenvalues ◽  
Dynamical Properties

Non-Hermitian quantum physics is used successfully for the description of different puzzling experimental results, which are observed in open quantum systems. Mostly, the influence of exceptional points on the dynamical properties of the system is studied. At these points, two complex eigenvalues Ei≡Ei+iΓi/2 of the non-Hermitian Hamiltonian H coalesce (where Ei is the energy and Γi is the inverse lifetime of the state i). We show that also the eigenfunctions Φi of the two states play an important role, sometimes even the dominant one. Besides exceptional points, other critical points exist in non-Hermitian quantum physics. At these points a=acr in the parameter space, the biorthogonal eigenfunctions of H become orthogonal. For illustration, we show characteristic numerical results.

scholarly journals EXCEPTIONAL POINTS IN OPEN AND PT-SYMMETRIC SYSTEMS

2014 ◽  
Vol 54 (2) ◽  
pp. 106-112 ◽  
Author(s):  
Hichem Eleuch ◽  
Ingrid Rotter
Keyword(s):  
Open Quantum Systems ◽  
Level Density ◽  
Quantum Systems ◽  
Point Of View ◽  
Eigenvalues And Eigenfunctions ◽  
Open Quantum ◽  
Exceptional Points ◽  
Characteristic Features ◽  
High Level ◽  
Symmetric Systems

Exceptional points (EPs) determine the dynamics of open quantum systems and cause also PT symmetry breaking in PT symmetric systems. From a mathematical point of view, this is caused by the fact that the phases of the wavefunctions (eigenfunctions of a non-Hermitian Hamiltonian) relative to one another are not rigid when an EP is approached. The system is therefore able to align with the environment to which it is coupled and, consequently, rigorous changes of the system properties may occur. We compare analytically as well as numerically the eigenvalues and eigenfunctions of a 2 × 2 matrix that is characteristic either of open quantum systems at high level density or of PT symmetric optical lattices. In both cases, the results show clearly the influence of the environment on the system in the neighborhood of EPs. Although the systems are very different from one another, the eigenvalues and eigenfunctions indicate the same characteristic features.

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