Robust CZ gate against flux line memory

• URL: http://arxiv.org/abs/2609.00939v1
• Date: Tue, 01 Sep 2026 09:00:39 GMT
• Title: Robust CZ gate against flux line memory
• Abstract summary: High-fidelity CZ gates are central to superconducting quantum processors.<n> Conventional predistortion, typically used for an isolated gate, can recover the desired flux at the chip but it fails if the flux line memory exists.<n>We model the flux line distortion as the dynamics of a stateful classical actuator coupled to a quantum system.
• Score: 0.6015898117103068
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: High-fidelity CZ gates are central to superconducting quantum processors, but implementations based on flux tuning are still sensitive to pulse distortion. Conventional predistortion, typically used for an isolated gate, can recover the desired flux at the chip but it fails if the flux line memory exists, causing the fidelity of repeated CZ gates to drop rapidly. To address this issue, we model the flux line distortion as the dynamics of a stateful classical actuator coupled to a quantum system. Using a first-order Dyson expansion, we derive the error generators induced by variations in the initial flux-line state. We then design a robust CZ gate by optimizing the flux pulse to suppress these generators and minimize the residual flux line state at the gate exit. A one-pole flux line model shows the expected first-order robustness plateau. For a more practical three-pole model, the optimized CZ pulse achieves $F_{\mathrm{avg}}=99.998\%$, suppresses all first-order error generators, and brings the residual flux line state close to zero. With no additional waiting time between gates, our robust pulse achieves $F_{\mathrm{avg}}=99.97\%$ for the complete ten-gate sequence and reduces the sequence infidelity by a factor of about $2.3\times10^{3}$ relative to the baseline under the same predistortion protocol. These results show that explicitly accounting for flux line memory maintains high-fidelity CZ operation across repeated gate sequences and addresses a key limitation of conventional predistortion.

Related papers

• Fast CZ gate in hybrid fluxonium-transmon systems with tunable couplers [16.326048933296303]
  We propose a high-fidelity controlled-Z (CZ) gate for a hybrid circuit comprising a fluxonium qubit, a fixed-frequency transmon qubit, and a flux-tunable transmon coupler.<n>By modulating only the external magnetic flux applied to the coupler, the qubit-qubit interaction is dynamically engineered for conditional-phase accumulation.<n> Numerical simulations demonstrate that a microwave-free CZ gate can be realized within $25 mathrmns$, with an average gate fidelity exceeding $99.99%$ and leakage below $10-5$.
  arXiv  Detail & Related papers  (2026-09-13T00:11:31Z)
• Conditional-squeezing gate in superconducting circuits [41.99844472131922]
  We present an implementation of a conditional-squeezing gate that squeezes a SQUID-terminated resonator mode along a direction determined by the state of a dispersively coupled qubit.<n>We use the gate to encode an arbitrary qubit state into superpositions of single- and two-mode squeezed states of the resonator.
  arXiv  Detail & Related papers  (2026-09-09T16:16:48Z)
• Robust controlled-Z gate for Rydberg atoms based on level-crossing-free echoing rapid adiabatic passage [6.740690920701749]
  We propose a controlled-Z gate scheme for Rydberg atoms based on level-crossing-free echoing rapid adiabatic population transfer.<n>We design antisymmetric Rabi frequency pulses and symmetric detuning pulses, enabling the system to completely avoid level-crossing points throughout the evolution.
  arXiv  Detail & Related papers  (2026-08-13T10:57:00Z)
• Error-Generator-Level Compression for Fast Quantum Gates [0.0]
  Fast quantum gates in multilevel systems require suppressing many coherent-error channels using pulses that remain simple to implement.<n>We introduce error-generator-level compression, a Magnus-based control principle that minimizes the complete projected error generator at a chosen perturbative order.<n>This construction preserves all modeled computational and leakage errors rather than truncating the pulse by error channel.
  arXiv  Detail & Related papers  (2026-07-31T00:46:27Z)
• Simple analytical flux-tuned iSWAP pulses for leakage suppression [0.15393457051344298]
  We present an analytical flux control method enabling derivative removal by adiabatic gate ($$-DRAG) for suppressing leakage in tunable flux two-qubit gates.<n>The method remains effective across a range of asymmetry between qubit anharmonicities and different circuit parameters, enabling high-fidelity two-qubit gates within the fifteen nanosecond range.
  arXiv  Detail & Related papers  (2026-06-11T08:34:58Z)
• Fault-tolerant simulation of the electronic structure using Projector Augmented-Waves and Bloch orbitals [43.936586633107396]
  We present the Bloch--UPAW framework that combines Bloch-orbital $k$-space structure with unitary projector-augmented-wave augmentation.<n>We derive a linear-combination-of-unitaries decomposition and a block-encoding circuit suitable for qubitization.<n>Asymptotically, the Toffoli cost scales as $mathcalO(N_k3)$ when refining the $k$-mesh and as $mathcalO(N_a3.5)$ when enlarging the supercell.
  arXiv  Detail & Related papers  (2026-04-13T23:46:58Z)
• CAWN: Continuous Acoustic Wave Networks for Autoregressive Language Modeling [46.16066322190728]
  We introduce the Continuous Acoustic Wave Network (CAWN), a fully continuous sequence-mixing architecture.<n>Instead of discrete matrix-based attention, CAWN projects hidden states into multi-headed complex-domain phasors.<n>To prevent signal degradation over ultra-long contexts, we introduce a dual-gated Selective Phase Resonance mechanism.
  arXiv  Detail & Related papers  (2026-04-05T20:13:22Z)
• Mitigating crosstalk errors for simultaneous single-qubit gates on a superconducting quantum processor [59.06950309601253]
  Single-qubit gates on superconducting quantum processors are typically implemented using microwave pulses applied through dedicated control lines.<n>These microwave pulses may also drive other qubits due to crosstalk arising from capacitive coupling and wavefunction overlap.<n>Crosstalk and frequency crowding increase errors during simultaneous single-qubit operations relative to isolated gates.
  arXiv  Detail & Related papers  (2026-03-11T17:47:32Z)
• Analytical blueprint for 99.999% fidelity X-gates on present superconducting hardware under strong driving [4.406638884109584]
  We numerically demonstrate gate infidelities below $10-5$ for a 7ns $$-rotation when incorporating existing decoherence rates.<n>We also answer long-standing questions about the optimal values of the DRAG prefactor as well as constant detuning.
  arXiv  Detail & Related papers  (2025-12-22T22:47:43Z)
• Control landscapes for high-fidelity generation of C-NOT and C-PHASE gates with coherent and environmental driving [41.94295877935867]
  We consider the problem of high fidelity generation of two-qubit C-NOT and C-PHASE (with a detailed study of C-Z) gates in presence of the environment. We study quantum control landscapes which describe the behaviour of the fidelity as a function of the controls.
  arXiv  Detail & Related papers  (2024-05-23T00:04:19Z)
• High-Fidelity, Frequency-Flexible Two-Qubit Fluxonium Gates with a Transmon Coupler [38.42250061908039]
  We propose and demonstrate an architecture for fluxonium-fluxonium two-qubit gates mediated by transmon couplers (FTF) FTF enables stronger couplings for gates using non-computational states while simultaneously suppressing the static controlled-phase entangling rate ($ZZ$) down to kHz levels. We show that FTF can be applied to a variety of fluxonium gate schemes to improve gate fidelities and passively reduce unwanted $ZZ$ interactions.
  arXiv  Detail & Related papers  (2023-04-12T18:08:53Z)
• High-fidelity Rydberg controlled-Z gates with optimal pulses [0.0]
  We numerically investigate the time-optimal pulses to generate a high-fidelity Rydberg $C_Z$ gate in a three-level ladder-type atomic system. Our results promise a high-fidelity and fast gate operation under amenable and controllable experimental parameters.
  arXiv  Detail & Related papers  (2023-03-29T02:16:49Z)
• Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module [39.5906786952554]
  We introduce a multi-chip module architecture to suppress phonon-mediated QP poisoning. We demonstrate an error per Clifford gate of 1.2(1)%, an order-of-magnitude reduction over the gate error achieved in the initial realization of SFQ-based qubit control.
  arXiv  Detail & Related papers  (2023-01-13T18:37:08Z)
• High fidelity two-qubit gates on fluxoniums using a tunable coupler [47.187609203210705]
  Superconducting fluxonium qubits provide a promising alternative to transmons on the path toward large-scale quantum computing. A major challenge for multi-qubit fluxonium devices is the experimental demonstration of a scalable crosstalk-free multi-qubit architecture. Here, we present a two-qubit fluxonium-based quantum processor with a tunable coupler element.
  arXiv  Detail & Related papers  (2022-03-30T13:44:52Z)
• Engineering fast bias-preserving gates on stabilized cat qubits [64.20602234702581]
  bias-preserving gates can significantly reduce resource overhead for fault-tolerant quantum computing. In this work, we apply a derivative-based leakage suppression technique to overcome non-adiabatic errors.
  arXiv  Detail & Related papers  (2021-05-28T15:20:21Z)

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.