{"project":[{"name":"NOMIS Fellowship Program","_id":"9B861AAC-BA93-11EA-9121-9846C619BF3A"},{"_id":"bdb108fd-d553-11ed-ba76-83dc74a9864f","name":"QUANTUM INFORMATION SYSTEMS BEYOND CLASSICAL CAPABILITIES / P5- Integration of Superconducting Quantum Circuits"}],"department":[{"_id":"GradSch"},{"_id":"JoFi"}],"file_date_updated":"2024-06-20T11:52:22Z","publication_status":"published","oa":1,"year":"2024","file":[{"access_level":"open_access","checksum":"258c353d47fa37ea63ea43b1e10a34a0","content_type":"application/pdf","file_name":"Thesis_main_final.pdf","creator":"fhassani","date_created":"2024-06-12T07:53:19Z","relation":"main_file","file_size":28370759,"file_id":"17137","date_updated":"2024-06-20T11:52:22Z"},{"access_level":"closed","checksum":"deffa5d0db88093f74812fa71520d5e1","date_created":"2024-06-12T07:54:27Z","creator":"fhassani","file_name":"Thesis_main.tex","content_type":"text/x-tex","file_size":445735,"relation":"source_file","file_id":"17138","date_updated":"2024-06-12T07:54:27Z"}],"date_created":"2024-06-11T18:20:05Z","article_processing_charge":"No","author":[{"first_name":"Farid","last_name":"Hassani","id":"2AED110C-F248-11E8-B48F-1D18A9856A87","full_name":"Hassani, Farid","orcid":"0000-0001-6937-5773"}],"language":[{"iso":"eng"}],"user_id":"8b945eb4-e2f2-11eb-945a-df72226e66a9","day":"11","tmp":{"legal_code_url":"https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode","image":"/images/cc_by_nc_sa.png","short":"CC BY-NC-SA (4.0)","name":"Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)"},"date_updated":"2024-06-20T12:38:44Z","status":"public","type":"dissertation","doi":"10.15479/at:ista:17133","degree_awarded":"PhD","month":"06","license":"https://creativecommons.org/licenses/by-nc-sa/4.0/","page":"161","oa_version":"Published Version","acknowledged_ssus":[{"_id":"NanoFab"},{"_id":"M-Shop"}],"date_published":"2024-06-11T00:00:00Z","keyword":["Quantum information","Qubits","Superconducting devices"],"ddc":["530"],"supervisor":[{"id":"4B591CBA-F248-11E8-B48F-1D18A9856A87","last_name":"Fink","first_name":"Johannes M","orcid":"0000-0001-8112-028X","full_name":"Fink, Johannes M"}],"abstract":[{"text":"An ideal quantum computer relies on qubits capable of performing fast gate operations and\r\nmaintaining strong interconnections while preserving their quantum coherence. Since the\r\ninception of experimental eforts toward building a quantum computer, the community has\r\nfaced challenges in engineering such a system. Among the various methods of implementing a\r\nquantum computer, superconducting qubits have shown fast gates close to tens of nanoseconds,\r\nwith the state-of-the-art reaching a coherence of a few milliseconds. However, achieving\r\nsimultaneously long lifetimes with fast qubit operations poses an inherent paradox. Qubits\r\nwith high coherence require isolation from the environment, while fast operation necessitates\r\nstrong coupling of the qubit. This thesis approaches this issue by proposing the idea of\r\nengineering superconducting qubits capable of transitioning between operating in a protected\r\nregime, where the qubit is completely isolated from the environment, and coupling to the\r\ncommunication channels as needed. In this direction, we use the geometric superinductor to\r\nscan the parameter space of rf-SQUID devices, searching for a regime where we can take the\r\nqubit protection to its extreme.\r\n\r\nThis leads us to the inductively shunted transmon (IST) regime, characterized by EJ /EC ≫ 1\r\nand EJ /EL ≫ 1, where the circuit potential exhibits a double well with a large barrier\r\nseparating the local ground states of each quantum well. In this regime, although it is\r\nanticipated that the two quantum wells would be isolated from each other, we observe single\r\nfuxon tunneling between them. The interplay of the cavity photons and the fuxon transition\r\nforms a rich physical system, containing resonance conditions that allow the preparation of the\r\nfuxon ground or excited states. This enables us to study the relaxation rate of such transition\r\nand show that it can be as large as 3.6 hours. Dynamically controlling the barrier height\r\nbetween the two quantum wells allows for controllable coupling, which scales exponentially,\r\nfor a qubit encoded in two fuxon states.\r\nThe 0-π qubit is one of the very few known superconducting circuit types that ofers exponential\r\nprotection from both relaxation and dephasing simultaneously. However, this qubit is not\r\nexempt from the fact that such protection comes at the expense of complex readout and\r\ncontrol. In this thesis, we propose a way to controllably break the circuit symmetry, the\r\nkey reason for the protection, to momentarily restore the ability to control and manipulate\r\nthe qubit. An asymmetry in capacitances and inductances in the 0-π circuit is detrimental\r\nsince they lead to coupling of the protected state to the thermally occupied parasitic mode\r\nof the circuit. However, here we try to exploit a controlled asymmetry in Josephson energies\r\nand show that this can be used as a tunable coupler between the protected states. In the\r\nfuture, this should allow to perform gate operations by dynamically controlling the asymmetry\r\ninstead of driving the protected transition with microwave pulses. Therefore, we believe that\r\nthe proposed method can make the use of protected qubits more practical in experimental\r\nrealizations of quantum computing.","lang":"eng"}],"has_accepted_license":"1","title":"Superconducting qubits capable of dynamic switching between protected and high-speed control regimes","_id":"17133","citation":{"mla":"Hassani, Farid. <i>Superconducting Qubits Capable of Dynamic Switching between Protected and High-Speed Control Regimes</i>. Institute of Science and Technology Austria, 2024, doi:<a href=\"https://doi.org/10.15479/at:ista:17133\">10.15479/at:ista:17133</a>.","ista":"Hassani F. 2024. Superconducting qubits capable of dynamic switching between protected and high-speed control regimes. Institute of Science and Technology Austria.","ieee":"F. Hassani, “Superconducting qubits capable of dynamic switching between protected and high-speed control regimes,” Institute of Science and Technology Austria, 2024.","chicago":"Hassani, Farid. “Superconducting Qubits Capable of Dynamic Switching between Protected and High-Speed Control Regimes.” Institute of Science and Technology Austria, 2024. <a href=\"https://doi.org/10.15479/at:ista:17133\">https://doi.org/10.15479/at:ista:17133</a>.","short":"F. Hassani, Superconducting Qubits Capable of Dynamic Switching between Protected and High-Speed Control Regimes, Institute of Science and Technology Austria, 2024.","apa":"Hassani, F. (2024). <i>Superconducting qubits capable of dynamic switching between protected and high-speed control regimes</i>. Institute of Science and Technology Austria. <a href=\"https://doi.org/10.15479/at:ista:17133\">https://doi.org/10.15479/at:ista:17133</a>","ama":"Hassani F. Superconducting qubits capable of dynamic switching between protected and high-speed control regimes. 2024. doi:<a href=\"https://doi.org/10.15479/at:ista:17133\">10.15479/at:ista:17133</a>"},"alternative_title":["ISTA Thesis"],"related_material":{"record":[{"status":"public","relation":"part_of_dissertation","id":"13227"},{"id":"9928","relation":"part_of_dissertation","status":"public"},{"id":"8755","relation":"part_of_dissertation","status":"public"}]},"publisher":"Institute of Science and Technology Austria","publication_identifier":{"isbn":["978-3-99078-040-4"],"issn":["2663-337X"]}}