Role of instabilities in the survival of quantum correlations (original) (raw)
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Quantum correlations in non-Markovian open quantum systems at different ranges of temperature
Laser Physics, 2018
In this paper, we numerically explore the quantum correlations in a system consisting of two identical qubits, each of them locally interacting with a bosonic reservoir under non-Markovian regime, dissipative quantum system. The influences of Ohmic reservoir with Lorentz–Drude regularization on the quantum discord and entanglement are studied. We analyze the quantum correlations rate in high temperature, intermediate temperature, and low temperature reservoirs, respectively. The dependence of the quantum correlations on the ratio r of the reservoir cutoff frequency and the system oscillator frequency, and temperature kBT shows that the decreasing of the frequency ratio r enhances the amount of quantum correlations between the two qubits, while the increasing of the temperature damages the amount of correlations. More precisely, we find a sudden death of quantum entanglement, that is, the entanglement vanishes as time becomes large for different temperatures. On the other hand, we show in contrast to what happens to entanglement, the quantum discord does not vanish even at high temperatures.
Evolution of quantum correlations in the open quantum systems consisting of two coupled oscillators
Quantum Information Processing, 2017
The open quantum systems consisting of coupled and uncoupled asymmetric oscillators are considered with an initial quantum-dot trapped-ion coherent state. The quantum correlations between spatial modes of this trapped ion are examined to find their dependence on the temperature, asymmetric parameter, dissipation coefficient and the magnetic field. It is observed that the discord of the initial state is an increasing function of the asymmetric parameter and the magnetic field. Moreover, in the case of two uncoupled modes, entanglement and discord are decreasing functions of temperature and the dissipation coefficient. However, as the temperature and dissipation coefficient increase, the discord fades out faster. In the case of two coupled modes, as the temperature and dissipation coefficient increase, the sudden death of the entanglement and fade out of the discord happen sooner; moreover, as the magnetic field increases, the entanglement sudden death and the discord fade out time occur sooner. Also, with the increase in the asymmetric parameter, the entanglement sudden death is postponed. In addition, in the asymmetric system, appreciable discord can be created in the temperature range 0-10 K, while appreciable entanglement can be created in the temperature range 0-5 mK. Finally, it is observed that non-monotonic evolution of quantum correlations is due to coupling of modes.
Post Markovian Dynamics of Quantum Correlations: Entanglement vs. Discord
2016
Dynamics of an open two-qubit system is investigated in the post-Markovian regime, where the environments have a short-term memory. Each qubit is coupled to separate environment which is held in its own temperature. The inter-qubit interaction is modeled by XY-Heisenberg model in the presence of spin-orbit interaction and inhomogeneous magnetic field. The dynamical behavior of entanglement and discord has been considered. The results show that, quantum discord is more robust than quantum entanglement, during the evolution. Also the asymmetric feature of quantum discord can be monitored by introducing the asymmetries due to inhomogeneity of magnetic field and temperature difference between the reservoirs. By employing proper parameters of the model, it is possible to maintain non-vanishing quantum correlation at high degree of temperature. The results can provide a useful recipe for studying of dynamical behavior of two-qubit systems such as trapped spin-electrons in coupled quantum ...
Quantum correlations and coherence between two particles interacting with a thermal bath
Journal of Physics A: Mathematical and Theoretical, 2017
Quantum correlations and coherence generated between two free spinless particles in the lattice, interacting with a common quantum phonon bath are studied. The reduced density matrix has been solved in the Markov approach. We show that the bath induces correlations between the particles. The coherence induced by the bath is studied calculating: off-diagonal elements of the density matrix, spatiotemporal dispersion, purity, and quantum mutual information. We have found a characteristic timescale pointing out when this coherence is maximum. In addition a Wigner-like distribution in the phase-space (lattice) has been introduced as an indirect indicator of the quantumness of total correlations and coherence induced by the thermal bath. The negative volume of the Wigner function shows also a behavior which is in agreement with the timescale that we have found. A Gaussian distribution for the profile of particles is not obtained and interference pattern are observed as the result of bath induced coherence. As the temperature of bath vanishes the ballistic behavior of the tight-binding model is recovered. The geometric quantum discord has been calculated to characterize the nature of the correlations.
Dynamics of quantum correlations in two-qubit systems within non-Markovian environments
International Journal of Modern Physics B 27, 1345053, 2012
Knowledge of the dynamical behavior of correlations with no classical counterpart, like entanglement, nonlocal correlations and quantum discord, in open quantum systems is of primary interest because of the possibility to exploit these correlations for quantum information tasks. Here we review some of the most recent results on the dynamics of correlations in bipartite systems embedded in non-Markovian environments that, with their memory effects, influence in a relevant way the system dynamics and appear to be more fundamental than the Markovian ones for practical purposes. Firstly, we review the phenomenon of entanglement revivals in a two-qubit system for both independent environments and a common environment. We then consider the dynamics of quantum discord in non-Markovian dephasing channel and briefly discuss the occurrence of revivals of quantum correlations in classical environments.
Does " cooling by heating " protect quantum correlations
The connection between nonequilibrium quantum correlations, such as entanglement and quantum discord, and cooling by heating is investigated for a system composed by two atoms interacting with a single electromagnetic mode of a lossy cavity. This Hamiltonian model is experimentally feasible in the quantum optics domain and presents the occurrence of both nonequilibrium quantum correlations and cooling by heating for a range of parameters. Since in the cooling by heating phenomenon the effective temperature of the system decreases even increasing the environments temperature, it could be expected that quantum correlations could be enhanced. Interestingly , for some parameters we show that, contrary to this expectation, in the case studied here the lowering of the system effective temperature leads to no enhancement in the quantum correlations. In addition, we found that at both zero and finite temperature , depending on the parameters used, quantum correlations can be enhanced even when increasing the damping rates, a somewhat counterintuitive result.
Dynamic entanglement in oscillating molecules
We demonstrate that entanglement can persistently recur in an oscillating two-spin molecule that is coupled to a hot and noisy environment, in which no static entanglement can survive. The system represents a non-equilibrium quantum system which, driven through the oscillatory motion, is prevented from reaching its (separable) thermal equilibrium state. Environmental noise, together with the driven motion, plays a constructive role by periodically resetting the system, even though it will destroy entanglement as usual. As a building block, the present simple mechanism supports the perspective that entanglement can exist also in systems which are exposed to a hot environment and to high levels of de-coherence, which we expect e.g. for biological systems. Our results furthermore suggest that entanglement plays a role in the heat exchange between molecular machines and environment. Experimental simulation of our model with trapped ions is within reach of the current state-of-the-art quantum technologies.
Chinese Physics Letters, 2011
We present a detailed study of the dynamics of correlations in non-Markovian environments, applying the hierarchy equations approach. This theoretical treatment is able to take the system-bath interaction into consideration carefully. It is shown that crosses and sudden changes of classical and quantum correlations can happen if we gradually reduce the strength of the interactions between qubits. For some special initial states, sudden transitions between classical and quantum correlations even occur.
System-reservoir dynamics of quantum and classical correlations
2010
We address the system-reservoir dynamics of classical and quantum correlations in the decoherence phenomenon, regarding a two qubit composite system interacting with two independent environments. The most common noise channels (amplitude damping, phase damping, bit flip, bit-phase flip, and phase flip) was studied. By analytical and numerical analysis we found that, contrary to what is usually stated in the literature, decoherence may occurs without entanglement between the system and the environment. We also found that, in some cases, the bipartite quantum correlation initially presented in the system is completely evaporated, it is not transferred to the environments.
Journal of Physics A: Mathematical and Theoretical, 2015
Quantum correlation lies at the very heart of almost all the non-classical phenomena exhibited by quantum systems composed of more than one subsystem. In the recent days it has been pointed out that there exists quantum correlation, namely discord which is more general than entanglement. Some authors have investigated that for certain initial states the quantum correlations as well as classical correlation exhibit sudden change under simple Markovian noise. We show that, this dynamical behavior of the both types of correlations can be explained using the idea of complementary correlations introduced in [arXiv:1408.6851]. We also show that though certain class of mixed entangled states can resist the monotonic decay of quantum correlations,it is not true for all mixed states. Moreover, pure entangled states of two qubits will never exhibit such sudden change.