Sharpening Worst-Case Error Assessment for Fault-Tolerant Quantum Computing: Fidelity and Its Deviation

• URL: http://arxiv.org/abs/2603.07495v1
• Date: Sun, 08 Mar 2026 06:35:40 GMT
• Title: Sharpening Worst-Case Error Assessment for Fault-Tolerant Quantum Computing: Fidelity and Its Deviation
• Abstract summary: We introduce a companion observable -- what we dub the fidelity deviation -- that quantifies how strongly the state-dependent fidelities fluctuate across input states.<n>For coherent (unitary) gate errors on two or more qubits, we show that the gate fidelity together with the fidelity deviation constrains the relevant spectral moments of the error unitary.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: Gate fidelity -- an average fidelity over all possible input states -- is the workhorse metric for benchmarking quantum gates or circuits, yet fault-tolerant quantum computing ultimately depends on the worst-case behavior, typically quantifiable by so-called the diamond distance. In the low-error regime, the coherent errors can inflate the worst-case error even when the reported gate fidelity is high, making the gate fidelity alone an unreliable proxy for fault-tolerance readiness. To capture the missing information, we introduce a companion observable -- what we dub the fidelity deviation -- that quantifies how strongly the state-dependent fidelities fluctuate across input states. Adopting such fluctuations in assessing the fault-tolerance is physically natural because some input directions are nearly unaffected while others form narrow "valleys" that dominate adversarial circuit behavior. For coherent (unitary) gate errors on two or more qubits, we show that the gate fidelity together with the fidelity deviation constrains the relevant spectral moments of the error unitary, enabling an explicit and tight certificate of the worst-case error. Both quantities are estimated directly from the same randomized input-measurement experiment, without full process tomography. We show that the fidelity and its deviation can provide an economical, operationally meaningful, and accurate standard for assessing the fault tolerance of the engineered quantum gates and circuits.

Related papers

• Analysis of Maximum Threshold and Quantum Security for Fault-Tolerant Encoding and Decoding Scheme Base on Steane Code [10.853582091917236]
  The original Steane code is not fault-tolerant because the CNOT gates in an encoded block may cause error propagation. We first propose a fault-tolerant encoding and decoding scheme, which analyzes all possible errors caused by each quantum gate in an error-correction period. We then provide the fault-tolerant scheme of the universal quantum gate set, including fault-tolerant preparation and verification of ancillary states.
  arXiv  Detail & Related papers  (2024-03-07T07:46:03Z)
• Error budget of parametric resonance entangling gate with a tunable coupler [0.0]
  We analyze the experimental error budget of parametric resonance gates in a tunable coupler architecture. Incoherent errors, mainly arising from qubit relaxation and dephasing due to white noise, limit the fidelity of the two-qubit gates. Leakage to noncomputational states is the second largest contributor to the two-qubit gates infidelity.
  arXiv  Detail & Related papers  (2024-02-06T18:46:27Z)
• Hamiltonian Phase Error in Resonantly Driven CNOT Gate Above the Fault-Tolerant Threshold [0.0]
  electron spin qubits are a promising platform for scalable quantum processors. A full-fledged quantum computer will need quantum error correction, which requires high-fidelity quantum gates. We demonstrate a simple yet reliable calibration procedure for a high-fidelity controlled-rotation gate in an exchange-always-on Silicon quantum processor.
  arXiv  Detail & Related papers  (2023-07-18T07:44:00Z)
• Demonstrating a long-coherence dual-rail erasure qubit using tunable transmons [59.63080344946083]
  We show that a "dual-rail qubit" consisting of a pair of resonantly coupled transmons can form a highly coherent erasure qubit. We demonstrate mid-circuit detection of erasure errors while introducing $ 0.1%$ dephasing error per check. This work establishes transmon-based dual-rail qubits as an attractive building block for hardware-efficient quantum error correction.
  arXiv  Detail & Related papers  (2023-07-17T18:00:01Z)
• Scalable evaluation of incoherent infidelity in quantum devices [0.0]
  We introduce the incoherent infidelity as a measure of incoherent errors. This method is applicable to generic quantum evolutions subjected to time-dependent Markovian noise. It provides an error quantifier for the target circuit, rather than an error averaged over many circuits or quantum gates.
  arXiv  Detail & Related papers  (2023-05-30T19:03:42Z)
• Witnessing entanglement in trapped-ion quantum error correction under realistic noise [41.94295877935867]
  Quantum Error Correction (QEC) exploits redundancy by encoding logical information into multiple physical qubits. We present a detailed microscopic error model to estimate the average gate infidelity of two-qubit light-shift gates used in trapped-ion platforms. We then apply this realistic error model to quantify the multipartite entanglement generated by circuits that act as QEC building blocks.
  arXiv  Detail & Related papers  (2022-12-14T20:00:36Z)
• Fidelity-based distance bounds for $N$-qubit approximate quantum error correction [0.0]
  Eastin-Knill theorem states that a quantum code cannot correct errors exactly, possess continuous symmetries, and implement a universal set of gates transversely. It is common to employ a complementary measure of fidelity as a way to quantify quantum state distinguishability and benchmark approximations in error correction. We address two distance measures based on the sub- and superfidelities as a way to bound error approximations, which in turn require a lower computational cost.
  arXiv  Detail & Related papers  (2022-12-08T16:10:58Z)
• Benchmarking quantum logic operations relative to thresholds for fault tolerance [0.02171671840172762]
  We use gate set tomography to perform precision characterization of a set of two-qubit logic gates to study RC on a superconducting quantum processor. We show that the average and worst-case error rates are equal for randomly compiled gates, and measure a maximum worst-case error of 0.0197(3) for our gate set.
  arXiv  Detail & Related papers  (2022-07-18T17:41:58Z)
• Robustness and Accuracy Could Be Reconcilable by (Proper) Definition [109.62614226793833]
  The trade-off between robustness and accuracy has been widely studied in the adversarial literature. We find that it may stem from the improperly defined robust error, which imposes an inductive bias of local invariance. By definition, SCORE facilitates the reconciliation between robustness and accuracy, while still handling the worst-case uncertainty.
  arXiv  Detail & Related papers  (2022-02-21T10:36:09Z)
• Analytical and experimental study of center line miscalibrations in M\o lmer-S\o rensen gates [51.93099889384597]
  We study a systematic perturbative expansion in miscalibrated parameters of the Molmer-Sorensen entangling gate. We compute the gate evolution operator which allows us to obtain relevant key properties. We verify the predictions from our model by benchmarking them against measurements in a trapped-ion quantum processor.
  arXiv  Detail & Related papers  (2021-12-10T10:56:16Z)
• Software mitigation of coherent two-qubit gate errors [55.878249096379804]
  Two-qubit gates are important components of quantum computing. But unwanted interactions between qubits (so-called parasitic gates) can degrade the performance of quantum applications. We present two software methods to mitigate parasitic two-qubit gate errors.
  arXiv  Detail & Related papers  (2021-11-08T17:37:27Z)
• Fault-tolerant parity readout on a shuttling-based trapped-ion quantum computer [64.47265213752996]
  We experimentally demonstrate a fault-tolerant weight-4 parity check measurement scheme. We achieve a flag-conditioned parity measurement single-shot fidelity of 93.2(2)%. The scheme is an essential building block in a broad class of stabilizer quantum error correction protocols.
  arXiv  Detail & Related papers  (2021-07-13T20:08:04Z)
• Crosstalk Suppression for Fault-tolerant Quantum Error Correction with Trapped Ions [62.997667081978825]
  We present a study of crosstalk errors in a quantum-computing architecture based on a single string of ions confined by a radio-frequency trap, and manipulated by individually-addressed laser beams. This type of errors affects spectator qubits that, ideally, should remain unaltered during the application of single- and two-qubit quantum gates addressed at a different set of active qubits. We microscopically model crosstalk errors from first principles and present a detailed study showing the importance of using a coherent vs incoherent error modelling and, moreover, discuss strategies to actively suppress this crosstalk at the gate level.
  arXiv  Detail & Related papers  (2020-12-21T14:20:40Z)

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.