---
_id: '17133'
abstract:
- lang: eng
  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."
acknowledged_ssus:
- _id: NanoFab
- _id: M-Shop
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Farid
  full_name: Hassani, Farid
  id: 2AED110C-F248-11E8-B48F-1D18A9856A87
  last_name: Hassani
  orcid: 0000-0001-6937-5773
citation:
  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>
  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>
  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>.
  ieee: F. Hassani, “Superconducting qubits capable of dynamic switching between protected
    and high-speed control regimes,” Institute of Science and Technology Austria,
    2024.
  ista: Hassani F. 2024. Superconducting qubits capable of dynamic switching between
    protected and high-speed control regimes. Institute of Science and Technology
    Austria.
  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>.
  short: F. Hassani, Superconducting Qubits Capable of Dynamic Switching between Protected
    and High-Speed Control Regimes, Institute of Science and Technology Austria, 2024.
corr_author: '1'
date_created: 2024-06-11T18:20:05Z
date_published: 2024-06-11T00:00:00Z
date_updated: 2026-01-07T11:18:31Z
day: '11'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: JoFi
doi: 10.15479/at:ista:17133
file:
- access_level: open_access
  checksum: 258c353d47fa37ea63ea43b1e10a34a0
  content_type: application/pdf
  creator: fhassani
  date_created: 2024-06-12T07:53:19Z
  date_updated: 2024-06-20T11:52:22Z
  file_id: '17137'
  file_name: Thesis_main_final.pdf
  file_size: 28370759
  relation: main_file
- access_level: closed
  checksum: deffa5d0db88093f74812fa71520d5e1
  content_type: text/x-tex
  creator: fhassani
  date_created: 2024-06-12T07:54:27Z
  date_updated: 2024-06-12T07:54:27Z
  file_id: '17138'
  file_name: Thesis_main.tex
  file_size: 445735
  relation: source_file
file_date_updated: 2024-06-20T11:52:22Z
has_accepted_license: '1'
keyword:
- Quantum information
- Qubits
- Superconducting devices
language:
- iso: eng
license: https://creativecommons.org/licenses/by-nc-sa/4.0/
month: '06'
oa: 1
oa_version: Published Version
page: '161'
project:
- _id: 9B861AAC-BA93-11EA-9121-9846C619BF3A
  name: NOMIS Fellowship Program
- _id: bdb108fd-d553-11ed-ba76-83dc74a9864f
  grant_number: F07105
  name: QUANTUM INFORMATION SYSTEMS BEYOND CLASSICAL CAPABILITIES / P5- Integration
    of Superconducting Quantum Circuits
publication_identifier:
  isbn:
  - 978-3-99078-040-4
  issn:
  - 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
  record:
  - id: '9928'
    relation: part_of_dissertation
    status: public
  - id: '13227'
    relation: part_of_dissertation
    status: public
  - id: '8755'
    relation: part_of_dissertation
    status: public
status: public
supervisor:
- first_name: Johannes M
  full_name: Fink, Johannes M
  id: 4B591CBA-F248-11E8-B48F-1D18A9856A87
  last_name: Fink
  orcid: 0000-0001-8112-028X
title: Superconducting qubits capable of dynamic switching between protected and high-speed
  control regimes
tmp:
  image: /images/cc_by_nc_sa.png
  legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
  name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC
    BY-NC-SA 4.0)
  short: CC BY-NC-SA (4.0)
type: dissertation
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
year: '2024'
...