Nonclassicality of open circuit QED systems in the deep-strong coupling regime
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 displace...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2021-01-01
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| Series: | New Journal of Physics |
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| Online Access: | https://doi.org/10.1088/1367-2630/ac2850 |
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| author | Tomohiro Shitara Motoaki Bamba Fumiki Yoshihara Tomoko Fuse Sahel Ashhab Kouichi Semba Kazuki Koshino |
| author_facet | Tomohiro Shitara Motoaki Bamba Fumiki Yoshihara Tomoko Fuse Sahel Ashhab Kouichi Semba Kazuki Koshino |
| author_sort | Tomohiro Shitara |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-03-12T16:28:25Z |
| format | Article |
| id | doaj.art-657c8b8eff474e6eae09af7b497dbfad |
| institution | Directory Open Access Journal |
| issn | 1367-2630 |
| language | English |
| last_indexed | 2024-03-12T16:28:25Z |
| publishDate | 2021-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | New Journal of Physics |
| spelling | doaj.art-657c8b8eff474e6eae09af7b497dbfad2023-08-08T15:37:36ZengIOP PublishingNew Journal of Physics1367-26302021-01-01231010300910.1088/1367-2630/ac2850Nonclassicality of open circuit QED systems in the deep-strong coupling regimeTomohiro Shitara0https://orcid.org/0000-0002-1799-9100Motoaki Bamba1https://orcid.org/0000-0001-9811-0416Fumiki Yoshihara2Tomoko Fuse3Sahel Ashhab4https://orcid.org/0000-0003-1931-1178Kouichi Semba5Kazuki Koshino6https://orcid.org/0000-0002-9754-4463College of Liberal Arts and Sciences, Tokyo Medical and Dental University , 2-8-30 Konodai, Ichikawa 272-0827, JapanThe Hakubi Center for Advanced Research, Kyoto University , Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan; PRESTO, Japan Science and Technology Agency , Kawaguchi 332-0012, Japan; Department of Physics I, Kyoto University , Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, JapanNational Institute of Information and Communications Technology , 4-2-1, Nukui-Kitamachi, Koganei, Tokyo 184-8795, JapanNational Institute of Information and Communications Technology , 4-2-1, Nukui-Kitamachi, Koganei, Tokyo 184-8795, JapanNational Institute of Information and Communications Technology , 4-2-1, Nukui-Kitamachi, Koganei, Tokyo 184-8795, Japan; Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University , Qatar Foundation, Doha, QatarNational Institute of Information and Communications Technology , 4-2-1, Nukui-Kitamachi, Koganei, Tokyo 184-8795, JapanCollege of Liberal Arts and Sciences, Tokyo Medical and Dental University , 2-8-30 Konodai, Ichikawa 272-0827, JapanWe 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.https://doi.org/10.1088/1367-2630/ac2850circuit QEDnonclassicalitydeep strong couplingmetrological power |
| spellingShingle | Tomohiro Shitara Motoaki Bamba Fumiki Yoshihara Tomoko Fuse Sahel Ashhab Kouichi Semba Kazuki Koshino Nonclassicality of open circuit QED systems in the deep-strong coupling regime New Journal of Physics circuit QED nonclassicality deep strong coupling metrological power |
| title | Nonclassicality of open circuit QED systems in the deep-strong coupling regime |
| title_full | Nonclassicality of open circuit QED systems in the deep-strong coupling regime |
| title_fullStr | Nonclassicality of open circuit QED systems in the deep-strong coupling regime |
| title_full_unstemmed | Nonclassicality of open circuit QED systems in the deep-strong coupling regime |
| title_short | Nonclassicality of open circuit QED systems in the deep-strong coupling regime |
| title_sort | nonclassicality of open circuit qed systems in the deep strong coupling regime |
| topic | circuit QED nonclassicality deep strong coupling metrological power |
| url | https://doi.org/10.1088/1367-2630/ac2850 |
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