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Noise Cross-Correlations from Single-Shot Measurements

J.S. Rojas-Arias1,*, P. Stano1,2, Y.-H. Wu3,4, L.C. Camenzind3, S. Tarucha1,3, and D. Loss1,5

  • *Contact author: juan.rojasarias@riken.jp
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PRX Quantum 7, 020351 – Published 4 June, 2026

DOI: https://doi.org/10.1103/1m1q-rvth

Abstract

We introduce Single-Shot Cross-Spectroscopy (SSCS), a method for extracting the auto- and cross-power spectral densities of dephasing noise in a qubit pair. The method uses straightforward input, namely, single-shot readouts from single-qubit Ramsey-type experiments, without requiring the reconstruction of qubit energy fluctuations from repeated measurements, and is resilient against errors in state preparation and measurement. We apply it to experimental data from a semiconductor spin-qubit device and obtain noise spectra over five orders of magnitude in frequency (5 mHz–500 Hz). Compared to other techniques, for spin qubits, SSCS enables access to noise correlations in the previously inaccessible intermediate-frequency range (1–500 Hz), and can be further extended with faster readout. The method is directly applicable to other qubit platforms, and the upper frequency it can probe is set by the repetition rate of a single-qubit preparation and measurement.

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Popular Summary

Noise is one of the main obstacles to building reliable quantum computers. While single-qubit noise has been widely studied, understanding how noise is correlated between qubits is equally important, since correlated errors can undermine error correction and limit scalability. However, measuring such correlations has been technically challenging. In this work, we introduce Single-Shot Cross-Spectroscopy (SSCS), a simple and general technique for mapping both auto- and cross-correlated noise spectra using only standard single-qubit Ramsey experiments. We demonstrate the method on a five-qubit silicon spin device, showing that it can cover a wide frequency range and extend the reach of existing approaches toward higher frequencies. This allows us to detect previously hidden noise features, such as peaks from electrical interference and signatures of fluctuators between qubits. SSCS provides a practical tool for characterizing noise in quantum hardware and guiding progress toward fault-tolerant quantum computation.

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PRX Quantum 7, 020351– Published 4 June, 2026
  • Received 29 September 2025
  • Revised 3 February 2026
  • Accepted 20 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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