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arXiv:1405.5002 · China Communications

Tuning quantum discord in Josephson charge qubits system

Bo-xing Shang, Weiwei Zhang, Yucui Guo, Xiaoqiang Xi

Published Jan 1, 2014• 0 citations
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Abstract

A type of two qubits Josephson charge system is constructed, and properties of the quantum discord (QD) as well as the differences between thermal QD and thermal entanglement are investigated. A detailed calculation shows that the magnetic flux is more efficient than the voltage in tuning QD. By choosing proper system parameter the maximum QD can be realized in our two qubits Josephson charge system.

DOI
10.1109/cc.2014.7022544

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We investigate how quantum correlations [quantum discord (QD)] of a two-qubit one-dimensional XYZ\mathit{XYZ}XYZ Heisenberg chain in thermal equilibrium depend on the temperature TTT of the bath and also on an external magnetic field BBB. We show that the behavior of thermal QD differs in many unexpected ways from thermal entanglement. For example, we show situations where QD increases with TTT when entanglement decreases, cases where QD increases with TTT even in regions with zero entanglement, and that QD signals a quantum phase transition even at finite TTT. We also show that by properly tuning BBB or the interaction between the qubits we get nonzero QD for any TTT and we present an effect not seen for entanglement, the ``regrowth'' of thermal QD.
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We investigate decoherence-free evolution (DFE) of quantum discord (QD) for two initially-correlated qubits in two finite-temperature reservoirs using an exactly solvable model. We study QD dynamics of the two qubits coupled to two independent Ohmic reservoirs when the two qubits are initially prepared in X-type quantum states. It is found that reservoir temperature significantly affects the DFE dynamics. We show that it is possible to control the DFE and to prolong the DFE time by choosing suitable parameters of the two-qubit system and reservoirs.