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Title: Nonclassicality of open circuit QED systems in the deep-strong coupling regime
Authors: Shitara, Tomohiro
Bamba, Motoaki  kyouindb  KAKEN_id  orcid https://orcid.org/0000-0001-9811-0416 (unconfirmed)
Yoshihara, Fumiki
Fuse, Tomoko
Ashhab, Sahel
Semba, Kouichi
Koshino, Kazuki
Author's alias: 馬場, 基彰
Issue Date: Oct-2021
Publisher: IOP Publishing
Journal title: New Journal of Physics
Volume: 23
Issue: 10
Thesis number: 103009
Abstract: We investigate theoretically how the ground state of a qubit–resonator (Q–R) system in the deep-strong coupling (DSC) regime is affected by the coupling to an environment. We employ as a variational ansatz for the ground state of the Q–R–environment system a superposition of coherent states displaced in qubit-state-dependent directions. We show that the reduced density matrix of the Q–R system strongly depends on how the system is coupled to the environment, i.e. capacitive or inductive, because of the broken rotational symmetry of the eigenstates of the DSC system in the resonator phase space. When the resonator couples to the qubit and the environment in different ways (for instance, one is inductive and the other is capacitive), the system is almost unaffected by the resonator–waveguide (R–W) coupling. In contrast, when the two couplings are of the same type (for instance, both are inductive), by increasing the R–W coupling strength, the average number of virtual photons increases and the quantum superposition realized in the Q–R entangled ground state is partially degraded. Since the superposition becomes more fragile with increasing the Q–R coupling, there exists an optimal coupling strength to maximize the nonclassicality of the Q–R system.
Rights: © 2021 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
URI: http://hdl.handle.net/2433/267493
DOI(Published Version): 10.1088/1367-2630/ac2850
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