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arXiv:1705.00887 · Open Systems & Information Dynamics

Non-Markovianity and Coherence of a Moving Qubit inside a Leaky Cavity

Ali Mortezapour, Mahdi Ahmadi Borji, DaeKil Park, Rosario Lo Franco

Published Sep 1, 2017• 27 citations
arXivHTMLPDF

Abstract

Non-Markovian features of a system evolution, stemming from memory effects, may be utilized to transfer, storage, and revive basic quantum properties of the system states. It is well known that an atom qubit undergoes non-Markovian dynamics in high quality cavities. Here we consider the qubit-cavity interaction in the case when the qubit is in motion inside a leaky cavity. We show that, owing to the inhibition of the decay rate, the coherence of the travelling qubit remains closer to its initial value as time goes by compared to that of a qubit at rest. We also demonstrate that quantum coherence is preserved more efficiently for larger qubit velocities. This is true independently of the evolution being Markovian or non-Markovian, albeit the latter condition is more effective at a given value of velocity. We however find that the degree of non-Markovianity is eventually weakened as the qubit velocity increases, despite a better coherence maintenance.

DOI
10.1142/s1230161217400066

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Non-Markovian features of a system evolution, stemming from memory effects, may be utilized to transfer, storage, and revive basic quantum properties of the system states. It is well known that an atom qubit undergoes non-Markovian dynamics in high quality cavities. Here we consider the qubit-cavity interaction in the case when the qubit is in motion inside a leaky cavity. We show that, owing to the inhibition of the decay rate, the coherence of the travelling qubit remains closer to its initial value as time goes by compared to that of a qubit at rest. We also demonstrate that quantum coherence is preserved more efficiently for larger qubit velocities. This is true independently of the evolution being Markovian or non-Markovian, albeit the latter condition is more effective at a given value of velocity. We however find that the degree of non-Markovianity is eventually weakened as the qubit velocity increases, despite a better coherence maintenance.
Abstract Efficient entanglement preservation in open quantum systems is a crucial scope towards a reliable exploitation of quantum resources. We address this issue by studying how two-qubit entanglement dynamically behaves when two atom qubits move inside two separated identical cavities. The moving qubits independently interact with their respective cavity. As a main general result, we find that under resonant qubit-cavity interaction the initial entanglement between two moving qubits remains closer to its initial value as time passes compared to the case of stationary qubits. In particular, we show that the initial entanglement can be strongly protected from decay by suitably adjusting the velocities of the qubits according to the non-Markovian features of the cavities. Our results supply a further way of preserving quantum correlations against noise with a natural implementation in cavity-QED scenarios and are straightforwardly extendable to many qubits for scalability.
The quantum speed limit (QSL) is a theoretical lower bound of the time required for a quantum system to evolve from an arbitrary initial state to its orthogonal counterpart. This figure can be used to characterize the dynamics of open quantum systems, including non-Markovian maps. In this paper, we investigate the QSL time for a model that consists of a single qubit moving inside a leaky cavity. Notably, we show that for both weak and strong coupling regimes, the QSL time increases while we boost the velocity of the qubit inside the leaky cavity. Moreover, it is observed that by increasing the qubit velocity, the speed of the evolution tends to a constant value, and the system becomes more stable. The results provide a better understanding of the dynamics of atom-photon couplings and can be used to enhance the controllability of quantum systems.
In this study, we consider a composed system consisting of two identical non-interacting subsystems. Each sub-system is made of a moving qubit into a leaky cavity. The study of the dynamic of the composed system revealed that compared with the stationary qubits, entanglement, quantum discord and coherence between two moving qubits remained close to their initial values as time went by. In particular, we show that the entanglement, quantum discord and the initial coherence between the two qubits could be strongly protected from decay by increasing the velocity of the qubits. Furthermore, based on such results, we have drawn a comparison between the three quantum resources (entanglement, quantum discord and coherence), demonstrating that the coherence of a bipartite system could be more robust than the two other quantum resources.
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.
Quantum coherence and non-Markovianity of an atom in a dissipative cavity under weak measurement are investigated in this work. We find that: the quantum coherence obviously depends on the initial atomic state, the strength of the weak measurement and its reversal, the atom–cavity coupling constant and the non-Markovian effect. It is obvious that the weak measurement effect protects the coherence better. The quantum coherence is preserved more efficiently for larger atom– cavity coupling. The stronger the non-Markovian effect is, the more slowly the coherence reduces. The quantum coherence can be effectively protected by means of controlling these physical parameters.
We investigate qubit entanglement dynamics in a two-qubit cavity system with stochastically fluctuating coupling strength, comparing white noise (Markovian) and Ornstein-Uhlenbeck noise (non-Markovian) processes. We analytically solve the system dynamics for both Fock and coherent cavity states and systematically characterize how initial qubit configurations affect entanglement generation and preservation. Our results reveal distinct dynamical regimes: in the Fock-state cavity, initial states in the single-excitation subspace generate robust qubit entanglement in decoherence-free subspaces, while initially entangled states in the double-excitation subspace exhibit inevitable decay without protective symmetries. For coherent cavities, we identify a critical photon-number threshold in the intermediate coherent-state amplitude regime where dynamics transition from low-frequency to high-frequency entanglement oscillations, while universal entanglement loss occurs at large amplitudes. Remarkable resilience against entanglement sudden death emerges under strong non-Markovian noise with long correlation times, where repeated revivals occur. These findings establish cavity photon statistics and environmental memory time as key control parameters for engineering qubit entanglement dynamics in qubit-cavity systems, revealing how system-environment correlations govern quantum information preservation.