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<p>Qubit frequency shifts, which often contain information about a target environment variable, are detected with Ramsey interference measurements. Unfortunately, the sensitivity of this protocol is limited by decoherence. We introduce a new protocol to enhance the sensitivity of a qubit frequency measurement in the presence of decoherence by applying a continuous drive to stabilize one component of the Bloch vector. We demonstrate our protocol on a superconducting qubit, enhancing sensitivity per measurement shot by 1.65&#xa0;× and sensitivity per qubit evolution time by 1.09&#xa0;× compared to Ramsey. We also explore the protocol theoretically, finding unconditional enhancements compared to Ramsey interferometry and maximum enhancements of 1.96&#xa0;× and 1.18&#xa0;×&#xa0;, respectively. Additionally, our protocol is robust to parameter miscalibrations. It requires no feedback and no extra control or measurement resources, and can be immediately applied in a wide variety of quantum computing and quantum sensor technologies.</p>

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Beating the Ramsey limit on sensing with deterministic qubit control

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年4月29日

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  • M. O. Hecht,
  • Kumar Saurav,
  • Evangelos Vlachos,
  • Daniel A. Lidar,
  • Eli M. Levenson-Falk

摘要

Qubit frequency shifts, which often contain information about a target environment variable, are detected with Ramsey interference measurements. Unfortunately, the sensitivity of this protocol is limited by decoherence. We introduce a new protocol to enhance the sensitivity of a qubit frequency measurement in the presence of decoherence by applying a continuous drive to stabilize one component of the Bloch vector. We demonstrate our protocol on a superconducting qubit, enhancing sensitivity per measurement shot by 1.65 × and sensitivity per qubit evolution time by 1.09 × compared to Ramsey. We also explore the protocol theoretically, finding unconditional enhancements compared to Ramsey interferometry and maximum enhancements of 1.96 × and 1.18 × , respectively. Additionally, our protocol is robust to parameter miscalibrations. It requires no feedback and no extra control or measurement resources, and can be immediately applied in a wide variety of quantum computing and quantum sensor technologies.