Revisiting the multi-mode rhombus circuit as a biased-noise qubit

• URL: http://arxiv.org/abs/2605.06430v1
• Date: Thu, 07 May 2026 15:34:54 GMT
• Title: Revisiting the multi-mode rhombus circuit as a biased-noise qubit
• Abstract summary: We revisit the idea of using an interferometer of pairs of Josephson junctions as a protected rhombus qubit.<n>Unlike in the original proposal, here, we intentionally alter the energy of one of the junctions to investigate the soft version of the rhombus qubit.<n>Our loss analysis on this multi-mode circuit indicates that at low frequencies, flux noise and quasiparticle tunneling limit the relaxation times.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: In this work, we revisit the idea of using an interferometer of pairs of Josephson junctions as a protected rhombus qubit. Unlike in the original proposal, where the qubit states are encoded into odd and even parity charge states, here, we intentionally alter the energy of one of the junctions to investigate the soft version of the rhombus qubit. This approach allows us to directly probe the qubit transitions over several GHz and reduce the potential drawbacks of the interferometer-based protection. Away from a half flux quantum external field, the large shunting capacitors of the circuit ensure localized qubit states in different phase valleys, leading to a biased-noise qubit. In the realized circuit, we measure an average $T_1\approx500\,μ$s relaxation time in the biased-noise regime (with a Ramsey dephasing time of $T^{R}_\varphi\approx90\,$ns), while an average $T_1\approx27\,μ$s relaxation time at frustration (with $T^{R}_\varphi\approx670\,$ns). Our loss analysis on this multi-mode circuit indicates that at low frequencies, flux noise and quasiparticle tunneling limit the relaxation times, pointing toward the presence of an optimal operating regime of around a few GHz.

Related papers

• The Gain-Engineered Transmon [68.89136228609398]
  We introduce and experimentally realize a noise-biased qubit in a standard transmon-readout resonator circuit.<n>Our results open a path towards using this system as a simple building-block for hardware-efficient quantum error detection and correction schemes.
  arXiv  Detail & Related papers  (2026-08-26T17:00:42Z)
• Coherence limitations of a Fourier-engineered $\cos(2\varphi)$ transmon qubit [1.77745925062582]
  Intrinsically protected superconducting qubits are a promising route toward enhancing coherence times and advancing hardware towards applications in quantum computing.<n>We experimentally realize a $cos(2varphi)$ qubit by Fourier engineering the energy-phase relation in a multi-junction superconducting circuit.<n>A fluxonium qubit with a similar energy spectrum and noise amplitude is less affected by flux noise, highlighting a key challenge for interference-based protection schemes.
  arXiv  Detail & Related papers  (2026-05-07T14:50:52Z)
• Coherence Limits in Interference-Based cos(2$\varphi$) Qubits [0.0]
  parity-protected $cos (2varphi)$ qubits based on interferences between two Josephson elements in a superconducting loop.<n>We show that qubit implementations of a $cos (2varphi)$ potential using a single loop can be described by the same Hamiltonian as two multi-harmonic Josephson junctions in a SQUID geometry.
  arXiv  Detail & Related papers  (2026-01-15T09:18:55Z)
• Gradiometric, Fully Tunable C-Shunted Flux Qubits [36.94429692322632]
  We present a capacitively shunted flux qubit featuring improved relaxation times up to T1 = 25 $mu$s.<n>As a model application, we demonstrate detection of two-level tunneling defects in a frequency range spanning one octave.
  arXiv  Detail & Related papers  (2025-09-30T09:51:16Z)
• Non-degenerate noise-resilient superconducting qubit [0.531628684262717]
  We propose a superconducting qubit based on engineering the first and second harmonics of the Josephson energy and phase relation.<n>By constructing a circuit such that $E_J2$ is negative and $|E_J1| ll |E_J2|$, we create a periodic potential with two non-degenerate minima.<n>The qubit, which we dub "harmonium", is formed from the lowest-energy states of each minimum.
  arXiv  Detail & Related papers  (2025-02-21T13:34:31Z)
• Viewing protected superconducting qubits through the lens of the cat qubit [0.4999814847776097]
  We draw analogies between protected superconducting qubits and bosonic qubits by studying the fluxonium Hamiltonian in its Fock basis.<n>We describe cat-qubit-inspired bias-preserving $X$ and $$$ qubits.
  arXiv  Detail & Related papers  (2025-01-27T19:00:01Z)
• Enhancing Dispersive Readout of Superconducting Qubits Through Dynamic Control of the Dispersive Shift: Experiment and Theory [47.00474212574662]
  A superconducting qubit is coupled to a large-bandwidth readout resonator. We show a beyond-state-of-the-art two-state-readout error of only 0.25,%$ in 100 ns integration time. The presented results are expected to further boost the performance of new and existing algorithms and protocols.
  arXiv  Detail & Related papers  (2023-07-15T10:30:10Z)
• Qubit readouts enabled by qubit cloaking [49.1574468325115]
  Time-dependent drives play a crucial role in quantum computing efforts. They enable single-qubit control, entangling logical operations, as well as qubit readout. Qubit cloaking was introduced in Lled'o, Dassonneville, et al.
  arXiv  Detail & Related papers  (2023-05-01T15:58:25Z)
• Cat-qubit-inspired gate on cos($2\theta$) qubits [77.34726150561087]
  We introduce a single-qubit $Z$ gate inspired by the noise-bias preserving gate of the Kerr-cat qubit. This scheme relies on a $pi$ rotation in phase space via a beamsplitter-like transformation between a qubit and ancilla qubit.
  arXiv  Detail & Related papers  (2023-04-04T23:06:22Z)
• Erasure qubits: Overcoming the $T_1$ limit in superconducting circuits [105.54048699217668]
  amplitude damping time, $T_phi$, has long stood as the major factor limiting quantum fidelity in superconducting circuits. We propose a scheme for overcoming the conventional $T_phi$ limit on fidelity by designing qubits in a way that amplitude damping errors can be detected and converted into erasure errors.
  arXiv  Detail & Related papers  (2022-08-10T17:39:21Z)
• Enhancing the Coherence of Superconducting Quantum Bits with Electric Fields [62.997667081978825]
  We show that qubit coherence can be improved by tuning defects away from the qubit resonance using an applied DC-electric field. We also discuss how local gate electrodes can be implemented in superconducting quantum processors to enable simultaneous in-situ coherence optimization of individual qubits.
  arXiv  Detail & Related papers  (2022-08-02T16:18:30Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.