Characterizing entanglement in non-Hermitian chaotic systems via out-of-time ordered correlators

We investigate the quantum entanglement in a non-Hermitian kicking system.In the Hermitian case,the out-of-time ordered correlators(OTOCs)exhibit the unbounded power-law increase with time.Correspondingly,the linear entropy,which is a common measurement of entanglement,rapidly increases from zero to almost unity,indicating the formation of quantum entanglement.For strong enough non-Hermitian driving,both the OTOCs and linear entropy rapidly saturate as time evolves.Interestingly,with the increase of non-Hermitian kicking strength,the long-time averaged value of both OTOCs and linear entropy has the same transition point where they exhibit the sharp decrease from a plateau,demonstrating the disentanglment.We reveal the mechanism of disentanglement with the extension of Floquet theory to non-Hermitian systems.

The performance of out-of-time events of the follow-up X-ray telescope onboard Einstein probe

Purpose:The purpose of this study is to investigate the performance of out-of-time events(OoT events)in the Follow-up X-ray Telescope(FXT)onboard the Einstein Probe.The OoT events,registered on the PN-CCD during its readout time,can provide information on the sources,e.g.,spectral indices,and diagnose the behavior of pile-up.Methods:In order to analyze the characteristics of OoT events,we simulated sources,each of which had been modeled using an absorbed power law combined with Gaussians,in different FXT modes and different luminosities.This allowed us to determine the OoT spectral indices and pile-up effect.Results:In the timing mode of FXT,the OoT events occupy a large proportion and the OoT correction must be done with the assumption that all photons originate from the source position on the CCD.While for some bright sources,the OoT events may be sufficient to derivate the source spectra,especially when pile-up occurs,particularly in the full frame mode and the partial window mode of FXT.Conclusion:We conclude that the OoT events can provide additional information about the celestial sources and can be used to estimate whether the pile-up occurs or not and the scope of pile-up.Furthermore,they can be also used to determine the new sources and improve the detection significance of a source.

Quantum instability and Ehrenfest time for an inverted harmonic oscillator

We use out-of-time order correlators(OTOCs)to investigate the quantum instability and Ehrenfest time for an inverted harmonic oscillator(IHO).For initial states located in the stable manifolds of the IHO we find that the corresponding OTOC exhibits identical evolutionary characteristics to the saddle point before the Ehrenfest time.For initial states located in the unstable manifolds,the OTOCs still grow exponentially but the time to maintain exponential growth is related to the center position of its wave packet in phase space.Moreover,we use the Husimi Q function to visualize the quantum wave packets during exponential growth of the OTOCs.Our results show that quantum instability exists at arbitrary orbits in the IHO system,and the Ehrenfest time in the IHO system depends not only on the photon number of the initial system but also on the central positions of the initial states in phase space.