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Journal of the Optical Society of America B

Quantum evolution speed in a double-layer environment

Kai Dong Xu, Guo‐Feng Zhang, Yue Ting Zhou, Wu‐Ming Liu

Published Feb 7, 2020• 2 citations
Publisher

Abstract

We investigate the dynamics of a two-level system in the presence of an overall environment composed of two layers. The first layer is just one single-mode cavity that decays to a memoryless reservoir while the second layer is two coupled single-mode cavities that decay to memoryless or memory-keeping reservoirs. We show that, in the weak-coupling regime between the qubit and the first-layer environment, the speed of evolution for the system can be controlled to a speeded-up or speeded-down process by manipulating the coupling strength in a double-layer environment. In particular, we find that multiple dynamics transitions from a not-speeded-up evolution to speeded-up evolution can be realized for the system by increasing the coupling strength in the second-layer environment. These results hold independently of the nature of the reservoirs in the second-layer environment.

DOI
10.1364/josab.383699

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We investigate the dynamics of a two-level system in the presence of an overall environment composed of two layers. The first layer is just one single-mode cavity that decays to a memoryless reservoir while the second layer is two coupled single-mode cavities that decay to memoryless or memory-keeping reservoirs. We show that, in the weak-coupling regime between the qubit and the first-layer environment, the speed of evolution for the system can be controlled to a speeded-up or speeded-down process by manipulating the coupling strength in a double-layer environment. In particular, we find that multiple dynamics transitions from a not-speeded-up evolution to speeded-up evolution can be realized for the system by increasing the coupling strength in the second-layer environment. These results hold independently of the nature of the reservoirs in the second-layer environment.
We investigate the dynamics of a two-level system in the presence of an overall environment composed of two layers. The first layer is just one single-mode cavity which decays to memoryless reservoir while the second layer is the two coupled single-mode cavities which decay to memoryless or memory-keeping reservoirs. In the weak-coupling regime between the qubit and the first-layer environment, our attention is focused on the effects of the coupling in the hierarchical environment on the non-Markovian speedup dynamics behavior of the system. We show that, by controlling the coupling in the second-layer environment, the multiple dynamics crossovers from Markovian to non-Markovian and from no-speedup to speedup can be realized. This results hold independently on the nature of the second-layer environment. Differently, we find that how the coupling between the two layers affects the non-Markovian speedup dynamics behavior depends on the nature of the second-layer environment.
Controlling the non-Markovian dynamics of open quantum systems is essential in quantum information technology since it plays a crucial role in preserving quantum memory. Albeit in many realistic scenarios the quantum system can simultaneously interact with composite environments, this condition remains little understood, particularly regarding the effect of the coupling between environmental parts. We analyze the non-Markovian behavior of a qubit interacting at the same time with two coupled single-mode cavities which in turn dissipate into memoryless or memory-keeping reservoirs. We show that increasing the control parameter, that is the two-mode coupling, allows for triggering and enhancing a non-Markovian dynamics for the qubit starting from a Markovian one in the absence of coupling. Surprisingly, if the qubit dynamics is non-Markovian for the zero control parameter, increasing the latter enables multiple transitions from non-Markovian to Markovian regimes. These results hold independently on the nature of the reservoirs. This work highlights that suitably engineering the coupling between parts of a compound environment can efficiently harness the quantum memory, stored in a qubit, based on non-Markovianity.
We investigate the qubit in the hierarchical environment where the first layer is just one lossy cavity while the second layer is the NNN-coupled lossy cavities. In the weak-coupling regime between the qubit and the first-layer environment, the dynamics crossovers from Markovian to non-Markovian and from no-speedup to speedup can be realized by controlling the hierarchical environment. We find that the coupling strength between two nearest-neighbor cavities and the number of cavities in the second-layer environment have the opposite effect on the non-Markovian dynamics and speedup evolution of the qubit. However, in the case of strong coupling between the qubit and the first-layer environment, we can be surprised to find that, compared with the original non-Markovian dynamics, the added second-layer environment cannot play a beneficial role on the speedup of the dynamics of the system. In addition, a phenomenon can be noticed that the complete opposite role of the coupling strength between two nearest-neighbor cavities (the number of cavities) in the second-layer environment in the above weak- and strong-coupling regimes.
We investigate the dynamics of an N -qubit interacting system coupled to a common reservoir. In the weak system-environment coupling regime, the crossovers from Markovian to non-Markovian and from no speedup to speedup can be realized by adjusting the controllable parameters (i.e., the coupling strength between qubits and the number of the qubits). However, in the case of strong coupling, the multiple transitions from non-Markovian regime to Markovian regime and from speedup to no speedup can be induced by manipulating controllable parameters. In addition, a phenomenon can be noticed that the number of qubits and the coupling strength between the qubits have the different effect on the non-Markovian dynamics and speedup evolution of the system in the above weak- and strong-coupling regimes. Our results provide an effective theoretical scheme for the realization of non-Markovian speedup dynamic processes. Published by the American Physical Society 2024
Quantum speedup of an open quantum system can be induced by the non-Markovian effect of the environment. Although an environment with a higher degree of non-Markovianity may seem like it should cause a faster speed of quantum evolution, this seemingly intuitive thinking may not always be correct. To clarify this point, we give a mechanism for controlling speedup of a single qubit that is coupled to a hierarchical photonic-crystal (PC) environment, which contains a defect single-mode cavity and a semi-infinite one-dimensional (1D) waveguide. Via studying the dynamics of the qubit, we reveal that with a judicious choice of the qubit-cavity coupling strength and the memory time of the waveguide environment, a speed-up evolution can be achieved. In particular, we found that the quantum speedup is not entirely attributed to the non-Markovianity, but to the increase of the total amount of flow information. That is the intrinsic physical reason that the hierarchical environment may induce the speed-up process. Our results may open new perspectives for detecting quantum speedup in realistic environments.
We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment-assisted speed-up is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms).