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Advances in Condensed Matter Physics

Entanglement Research for the Coupled Superconducting Phase Qubit and a Two-Level System

Jianxin Shi

Published Sep 21, 2020• 5 citations
Publisher

Abstract

Entanglement can exist not only in the microscopic system (e.g., atom, photon, and ion trap) but also in macroscopic systems. According to recent research, entanglement can be achieved and controlled in superconducting devices. The quantum dynamics and entanglement mechanism of the coupled superconducting phase qubit and a two-level system (TLS) were demonstrated when the bipartite system was under microwave driving. Besides, the results reveal that when the system was experiencing decoherence, entanglement (concurrence) of the coupled superconducting phase qubit and TLS would oscillate damply with microwave driving time, even exhibiting concurrence sudden death and revival. The coupling effect of the superconducting qubit and TLS system and the resonant microwave together help to achieve entanglement, while concurrence death and concurrence revival are dependent on the decoherence source and mechanism, for example, the resonant microwave driving time acting on the bipartite coupling system. Furthermore, the simulation results show the entanglement of the coupled qubit and TLS system also depends on the purity of the initial states of the system. The article carried out a numerical simulation on the entanglement of different initial states, and the results showed that the entanglement of the coupled system changes with different initial states. For different initial states, entanglement, sudden death, and rejuvenation are still visible.

DOI
10.1155/2020/3838106

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Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA(Dated: November 23, 2011)We report the observation and quantitative characterization of driven and spontaneous oscilla-tions of quantum entanglement, as measured by concurrence, in a bipartite system consisting of amacroscopic Josephson phase qubit coupled to a microscopic two-level system. The data clearlyshow the remarkable behavior of entanglement dynamics such as sudden death and revival, and thee ect of decoherence and ac driving on entanglement.
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We present an analytical and comprehensive description of the quantum dynamics of a microwave resonantly driven superconducting phase qubit coupled to a microscopic two-level system (TLS), covering a wide range of the external microwave field strength. Our model predicts several interesting phenomena in such an ac driven four-level bipartite system including anomalous Rabi oscillations, high-contrast beatings of Rabi oscillations, and extraordinary two-photon transitions. Our experimental results in a coupled qubit-TLS system agree quantitatively very well with the predictions of the theoretical model.