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quantum speed limits of a qubit system interacting with a nonequilibrium environment

Chinese Physics B 2016年第8期25卷 30-38页

作者：贺志姚春梅李莉王琼 College of Physics and Electronics Hunan University of Arts and Science

The speed of evolution of a qubit undergoing a nonequilibrium environment with spectral density of general ohmic form is investigated. First we reveal non-Markovianity of the model, and find that the non-Markovianity quantified by information backflow of Breuer et al. [Phys. Rev. Lett. 103 210401（2009）] displays a nonmonotonic behavior for different values of the ohmicity parameter s in fixed other parameters and the maximal non-Markovianity can be achieved at a specified value s. We also find that the non-Markovianity displays a nonmonotonic behavior with the change of a phase control parameter. Then we further discuss the relationship between quantum speed limit（QSL） time and non-Markovianity of the open-qubit system for any initial states including pure and mixed states. By investigation, we find that the QSL time of a qubit with any initial states can be expressed by a simple factorization law： the QSL time of a qubit with any qubitinitial states are equal to the product of the coherence of the initial state and the QSL time of maximally coherent states,where the QSL time of the maximally coherent states are jointly determined by the non-Markovianity, decoherence factor and a given driving time. Moreover, we also find that the speed of quantum evolution can be obviously accelerated in the wide range of the ohmicity parameter, i.e., from sub-Ohmic to Ohmic and super-Ohmic cases, which is different from the thermal equilibrium environment case.

关键词： quantum speed limits non-Markovianity nonequilibrium environment

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quantum speed limit of the double quantum dot in pure dephasing environment under measurement

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Chinese Physics B 2022年第7期31卷 146-151页

作者： Zhenyu Lin Tian Liu Zongliang Li Yanhui Zhang Kang Lan School of Physics and Electronics Shandong Normal UniversityJinan 250014China School of Physics State Key Laboratory of Crystal MaterialsShandong UniversityJinan 250100China

The quantum speed limit(QSL)of the double quantum dot(DQD)system has been theoretically investigated by adopting the detection of the quantum point contact(QPC)in the pure dephasing *** Mandelstam–Tamm(MT)type of the QSL bound which is based on the trace distance has been extended to the DQD system for calculating the shortest evolving *** increase of decoherence rate can weaken the capacity for potential speedup(CPS)and delay the evolving process due to the frequently measurement localizing the electron in the DQD *** system needs longer time to evolve to the target state as the enhancement of dephasing rate,because the strong interaction between pure dephasing environment and the DQD system could vary the oscillation of the *** the dephasing rate can sharp the QSL bound,but the decoherence rate would weaken the former effect and vice ***,the CPS would be raised by increasing the energy displacement,while the enhancement of the coupling strength between two quantum dots can diminish *** is interesting that there has an inflection point,when the coupling strength is less than the value of the point,the increasing effect of the CPS from the energy displacement is dominant,otherwise the decreasing tendency of the CPS is determined by the coupling strength and suppress the action of the energy displacement if the coupling strength is greater than the *** results provide theoretical reference for studying the QSL time in a semiconductor device affected by numerous factors.

关键词： quantum speed limits the DQD system the pure dephasing environment quantum measurement

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Non-Markovian speedup dynamics control of the damped Jaynes-Cummings model with detuning

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Chinese Physics B 2018年第1期27卷 247-252页

作者：徐凯韩伟张英杰范桁 Shandong Provincial Key Laboratory of Laser Polarization and Information Technology Department of Physics Qufu Normal University Beijing National Laboratory of Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Collaborative Innovation Center of quantum Matter

For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment （the lossy cavity field）. We mainly focus on the effects of the qubit--cavity detuning A and the qubit-cavity coupling strength k on the non-Markovian speedup evolution of an open system. By controlling the environment, i.e., tuning zl and , two dynamical crossovers from Markovian to non-Markovian and from no-speedup to speedup are achieved. Furthermore, it is clearly found that increasing the coupling strength k or detuning A in some cases can make the environmental non-Markovianity stronger and hence can lead to faster evolution of the open system.

关键词： non-Markovianity quantum speed limits open system dynamics

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