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Chinese Physics Letters

Linear Entropy and Entanglement in Two-Charge-Qubit Circuits

Liao Qing-Hong, Fang Guang-Yu, Wang Yue-Yuan, Ahmad Muhammad Ashfaq, Shutian Liu

Published Jul 1, 2010• 4 citations
Publisher

Abstract

We consider a model that contains two coupled superconducting charge qubits by sharing a large Josephson junction. We examine the dynamical properties of the linear entropy of two qubits and the probability of both qubits being in an excited state. The results show that the initial mean photon number, the initial phase of the field and the relative phase of the two qubits' levels play an important role in the evolution of the linear entropy of the two qubits and the probability.

DOI
10.1088/0256-307x/27/7/070304

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We consider a model that contains two coupled superconducting charge qubits by sharing a large Josephson junction. We examine the dynamical properties of the linear entropy of two qubits and the probability of both qubits being in an excited state. The results show that the initial mean photon number, the initial phase of the field and the relative phase of the two qubits' levels play an important role in the evolution of the linear entropy of the two qubits and the probability.
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Quantum correlations are considered analytically in a model that contains two coupled superconducting charge qubits sharing a large Josephson junction. Dynamical properties for the reduced two-qubit state are addressed in the quantum evolution when the coupling between the field and the qubits is either constant or time-dependent. In the latter case, adiabatic and nonergodic features are present for extremely low and fast evolutions, respectively. Finally, the case where the coupling drops to zero is also considered.
This paper investigates theoretically the evolutions of the entanglement entropy of a system of two coupled-chargequbits interacting with an LC -resonator. It is found that when the initial states of the two qubits are prepared in a given superposition excited state, the evolution of the von Neumann entropy of the system depends significantly on the coupling strength between the two Josephson charge qubits. With the variation of the coupling strength, the evolution of the entanglement entropy of the system forms some structures, especially the periodically bistable properties, which are the first discovered for such a system to our knowledge. It is found that the relative entropy entanglement of the system is also sensitive to the variation of the coupling strength between the two charge qubits, some novel ‘collective oscillations’ of the relative entropy are found for the system.
We investigate the entanglement properties of two superconducting charge qubits that share a large Josephson junction where the field is assumed to be prepared initially in a Glauber–Lachs state. We explore the increasing effect of the chaotic field due to the thermal photons on the entanglement properties of these two superconducting charge qubits. We show that the entanglement of the qubits is very sensitive to thermal photons. The chaotic effect of the field has a reducing effect on the entanglement degree of the qubits. Also, we draw a parallelism between the Glauber–Lachs state and the random telegraph noise by means of the entanglement.