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Physica Scripta

Entanglement of two superconducting charge qubits with the Glauber–Lachs state

Hünkar Kayhan

Published Apr 5, 2011• 2 citations
Publisher

Abstract

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.

DOI
10.1088/0031-8949/83/05/055003

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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.
We consider a model which consists of two coupled superconducting charge qubits by sharing a large Josephson junction. The time evolution of entanglement between two Josephson charge qubits is investigated by employing the concurrence. We examine the influence of the initial mean photon number, the relative phase and the amplitude of the two qubits on the time evolution of entanglement. The results show that the initial mean photon number, the relative phase and the amplitude of the two qubits play an important role in the evolution of entanglement.
In this paper, we investigated the dynamics of entanglement of two identical charge qubits with Josephson junctions in the case when one of the qubits is exposed to a microwave field in a coherent or thermal state. We have found the exact solution of the quantum time equation of evolution of the system under consideration for the statistical operator in the case of initial separable and entangled states of qubits. The exact solution for the complete statistical operator is used to calculate the qubit entanglement criterion - concurrence. The results of numerical simulation of the time dependence of the concurrence in the case of the coherent field showed that, with a certain choice of model parameters, the system can realize long-lived entangled states. It is also shown that for the thermal state of the field and the entangled initial state of qubits, the qubits retain a certain degree of entanglement during evolution even in the case of very intensive fields. In this case, for any intensities of thermal noise, there is no effect of the sudden death of entanglement.
We study the dynamics of the entropy correlations and entanglement in a system of interaction of a superconducting charge qubit with a single-mode resonant cavity subject to noise considered as two-state random phase telegraph noise. We show that although the noise has an apparent suppressing effect on the evolution of the entropies of the qubit and the field and also on the entanglement in the system, the entropy exchange between the qubit and the field is independent of it during the time evolution of the system.
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.