Singlet-only always-on gapless exchange (SAGE) spin qubits: Charge noise effects and two-qubit gates

• URL: http://arxiv.org/abs/2604.15419v1
• Date: Thu, 16 Apr 2026 17:58:51 GMT
• Title: Singlet-only always-on gapless exchange (SAGE) spin qubits: Charge noise effects and two-qubit gates
• Abstract summary: Singlet-only always-on gapless exchange (SAGE) spin qubits are an alternative type of exchange-only (EO) qubits.<n>We study the performance of SAGE qubits in the presence of $1/f$ charge noise.<n>We propose a simple refocusing strategy to mitigate the noise, while increased ramp times of the entangling pulse suppress leakage into noncomputational states.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Singlet-only always-on gapless exchange (SAGE) spin qubits are an alternative type of exchange-only (EO) qubits that encode a single qubit in the spins of four electrons located in four tunnel-coupled quantum dots. While conventional EO qubits are susceptible to local magnetic field gradients caused by local nuclear environments and $g$-factor variations, the SAGE qubit subspace is inherently protected from magnetic-gradient-induced Pauli errors by virtue of the singlet-only encoding, which is invariant under magnetic field gradients, and the always-on exchange couplings, which provide energetic leakage protection. However, the always-on operation simultaneously increases the qubit's sensitivity to charge noise. Here, starting from a Hubbard model describing the underlying electronic structure of the coupled quantum dots, we characterize the performance of SAGE qubits in the presence of $1/f$ charge noise that induces fluctuations in both the dot chemical potentials and the interdot tunnel couplings. We calculate SAGE idle coherence times and show that realistic CPMG-like pulse sequences can be used to significantly extend SAGE single-qubit coherence times for experimentally relevant charge noise strengths. We likewise study the fidelity of SAGE two-qubit gates in the presence of charge and magnetic noise and again propose a simple refocusing strategy to mitigate the noise, while increased ramp times of the entangling pulse suppress leakage into noncomputational states.

Related papers

• All-electrical dephasing-protected spin qubits in altermagnets [0.0]
  We propose altermagnetic semiconductors as a platform for field-free, all-electrically controlled spin qubits in gate-defined quantum dots.<n>We show that electric-dipole spin resonance enables single-qubit control, while tunable exchange and electrically addressable qubit frequencies realize fSim two-qubit gates.
  arXiv  Detail & Related papers  (2026-06-24T17:44:02Z)
• Noise-protected two-qubit gate using anisotropic exchange interaction [0.0]
  Hole spin qubits hosted in Germanium quantum dots are promising candidates for scalable quantum computing.<n>We propose a novel two-qubit gate protocol for Germanium hole spin qubits operated in the gapless regime.
  arXiv  Detail & Related papers  (2026-03-13T14:48:25Z)
• Singlet-only Always-on Gapless Exchange Qubits with Baseband Control [0.0]
  We propose a singlet-only always-on gapless exchange (SAGE) spin qubit that encodes a single qubit in the spins of four electrons.<n>We find that when magnetic noise dominates over charge noise, coherence times and single-qubit gate infidelities of the SAGE qubit improve by an order of magnitude compared to conventional exchange-only qubits.
  arXiv  Detail & Related papers  (2025-01-30T18:59:10Z)
• Passive and active suppression of transduced noise in silicon spin qubits [0.0]
  We show open- and closed-loop suppression techniques for the transduced noise in silicon spin qubits. We show that adaptive qubit control also reduces the non-Markovian noise in the system. The technique can be used to learn multiple Hamiltonian parameters and is useful for the intermittent calibration of the circuit parameters.
  arXiv  Detail & Related papers  (2024-03-05T05:44:23Z)
• 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)
• Autonomous coherence protection of a two-level system in a fluctuating environment [68.8204255655161]
  We re-examine a scheme originally intended to remove the effects of static Doppler broadening from an ensemble of non-interacting two-level systems (qubits) We demonstrate that this scheme is far more powerful and can also protect a single (or even an ensemble) qubit's energy levels from noise which depends on both time and space.
  arXiv  Detail & Related papers  (2023-02-08T01:44:30Z)
• Stabilizing and improving qubit coherence by engineering noise spectrum of two-level systems [52.77024349608834]
  Superconducting circuits are a leading platform for quantum computing. Charge fluctuators inside amorphous oxide layers contribute to both low-frequency $1/f$ charge noise and high-frequency dielectric loss. We propose to mitigate those harmful effects by engineering the relevant TLS noise spectral densities.
  arXiv  Detail & Related papers  (2022-06-21T18:37:38Z)
• Learning Noise via Dynamical Decoupling of Entangled Qubits [49.38020717064383]
  Noise in entangled quantum systems is difficult to characterize due to many-body effects involving multiple degrees of freedom. We develop and apply multi-qubit dynamical decoupling sequences that characterize noise that occurs during two-qubit gates.
  arXiv  Detail & Related papers  (2022-01-26T20:22:38Z)
• Charge noise suppression in capacitively coupled singlet-triplet spin qubits under magnetic field [6.211541620389987]
  We show that a range of nearly sweet spots appear in the coupled singlet-triplet qubit system when a strong enough magnetic field is applied externally. We further demonstrate that ramping to and from the judiciously chosen nearly sweet spot using sequences based on the shortcut to adiabaticity offers maximal gate fidelities under charge noise and phonon-induced decoherence.
  arXiv  Detail & Related papers  (2020-11-18T16:36:50Z)
• Probing the coherence of solid-state qubits at avoided crossings [51.805457601192614]
  We study the quantum dynamics of paramagnetic defects interacting with a nuclear spin bath at avoided crossings. The proposed theoretical approach paves the way to designing the coherence properties of spin qubits from first principles.
  arXiv  Detail & Related papers  (2020-10-21T15:37:59Z)
• Universal non-adiabatic control of small-gap superconducting qubits [47.187609203210705]
  We introduce a superconducting composite qubit formed from two capacitively coupled transmon qubits. We control this low-frequency CQB using solely baseband pulses, non-adiabatic transitions, and coherent Landau-Zener interference. This work demonstrates that universal non-adiabatic control of low-frequency qubits is feasible using solely baseband pulses.
  arXiv  Detail & Related papers  (2020-03-29T22:48:34Z)

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.