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ACTA PHOTONICA SINICA

Disentanglement and Decoherence in the Three-qubit System

Ming‐Liang Hu

Published Jan 1, 2008• 0 citations
OpenAlex

Abstract

The disentanglement and decoherence in the three-qubit system are studied based on the model of reservoir of harmonic oscillators by solving the non-Markovian approximation master equation,in which they are caused by a pure dephasing process.The GHZ-class state,W-class state and WGHZ-class state are discussed in detail.In all cases,the time scales of the decoherence and disentanglement are obtained.For the initial GHZ-class state,the coherence and entanglement decay completely;for the initial W-class state,the decoherence and disentanglement do not occur;for the initial WGHZ-class state,the decoherence happens partly,and the entanglement varies with time firstly and then becomes a certain asymptotic value.

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The disentanglement and decoherence in the three-qubit system are studied based on the model of reservoir of harmonic oscillators by solving the non-Markovian approximation master equation,in which they are caused by a pure dephasing process.The GHZ-class state,W-class state and WGHZ-class state are discussed in detail.In all cases,the time scales of the decoherence and disentanglement are obtained.For the initial GHZ-class state,the coherence and entanglement decay completely;for the initial W-class state,the decoherence and disentanglement do not occur;for the initial WGHZ-class state,the decoherence happens partly,and the entanglement varies with time firstly and then becomes a certain asymptotic value.
The decoherence of entanglement of two-qubit states is investigated by means of the non-Markovian quantum master equation. It is assumed that the decoherence is caused by environmental systems in non-stationary states, which evolve from initial states into equilibrium states. In this case, the non-Markovian nature of the environmental systems is of essential importance. It is shown that the disentanglement time after which there is no qubit entanglement is determined by the non-Markovian effect and the thermal effect of the environmental systems.
The decoherence of two initially entangled qubits coupled with a squeezed vacuum cavity separately is investigated exactly. The results show that, first, in principle, the disentanglement time decreases with the increase of squeeze parameter r, due to the augmenting of average photon number of every mode in the squeezed vacuum cavity. Second, there appear entanglement revivals after the complete disentanglement for the case of even parity initial Bell state, while there occur the entanglement decrease and the entanglement revival before the complete disentanglement for the case of odd parity initial Bell state. The results are quite different from those for the case of qubits in a vacuum cavity.
We study the non-Markovian decoherence and disentanglement dynamics of dissipative quantum systems with special emphasis on non-Gaussian continuous variable systems. The dynamics are described by the Hu–Paz–Zhang master equation of quantum Brownian motion. The time evolution of the decoherence function of a single-mode superposition is compared to the concurrence of a two-mode entangled state. It is verified that moderate non-Markovian influences slow down the decay of interference fringes and quantum correlations, while strong non-Markovian effects resulting from an out-of-resonance bath can even accelerate the loss of coherence, compared to predictions of Markovian approximations. Qualitatively different scenarios including exponential, Gaussian or algebraic decay of the decoherence function are analyzed. It is shown that partial revivals of coherence can occur in case of non-Lindblad-type dynamics.
We study the non-Markovian decoherence and disentanglement dynamics of dissipative quantum systems with special emphasis on non-Gaussian continuous variable systems. The dynamics are described by the Hu-Paz-Zhang master equation of quantum Brownian motion. The time evolution of the decoherence function of a single-mode superposition is compared to the concurrence of a two-mode entangled state. It is verified that moderate non-Markovian influences slow down the decay of interference fringes and quantum correlations, while strong non-Markovian effects resulting from an out-of-resonance bath can even accelerate the loss of coherence, compared to predictions of Markovian approximations. Qualitatively different scenarios including exponential, Gaussian or algebraic decay of the decoherence function are analyzed. It is shown that partial revivals of coherence can occur in case of non-Lindblad-type dynamics.
The decoherence of two initially entangled qubits in a squeezed vacuum cavity has been investigated exactly. The results show that, first, in principle, the disentanglement time decreases with the increasing of squeeze parameter r, due to the augmenting of average photon number of every mode in squeezed vacuum cavity. Second, there are entanglement revivals after complete disentanglement for the case of even parity initial Bell state, while there are entanglement decrease and revival before complete disentanglement for the case of odd parity initial Bell state. The results are quite different from that of the case for qubits in a vacuum cavity.
We determine the total state dynamics of a dephasing open quantum system using the standard environment of harmonic oscillators. Of particular interest are random unitary approaches to the same reduced dynamics and system-environment correlations in the full model. Concentrating on a model with an at times negative dephasing rate, the issue of non-Markovianity will also be addressed. Crucially, given the quantum environment, the appearance of non-Markovian dynamics turns out to be accompanied by a loss of system-environment correlations. Depending on the initial purity of the qubit state, these system-environment correlations may be purely classical over the whole relevant time scale, or there may be intervals of genuine system-environment entanglement. In the latter case, we see no obvious relation between the build-up or decay of these quantum correlations and Non-Markovianity.