Sequential Measurements as a Resource in Ancilla-Assisted Quantum Metrology

Abstract

We present a protocol for simultaneous estimation of both quadratures of a displacement channel on a quantum harmonic oscillator using a single ancilla qubit, without complex state preparation or adaptive control. The qubit is coupled to the quantum harmonic oscillator via controlled displacements of strength A and undergoes N rounds of measurement and reset, while the oscillator coherently accumulates the displacement signal. The non-commuting displacements imprint an order-dependent geometric phase at each round, giving a quantum Fisher information that scales as 𝒪(A² N³). Although the measurement record space grows as 2^N, we show that exact likelihoods for any individual measurement record can be computed in 𝒪(N²) time. With this, we show that measurement in the computational basis approximately saturates the quantum bound and maintains the 𝒪(A² N³) scaling. Furthermore, the periodic information extraction makes the protocol robust to decoherence. Our results provide a framework for the design and analysis of sequential measurement in ancilla-assisted protocols.

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BibTeX RIS

BibTeX

@misc{mentesoglu2026sequential,
  title = {{Sequential Measurements as a Resource in Ancilla-Assisted Quantum Metrology}},
  author = {Koray Mentesoglu and Rahul Trivedi and Sara Mouradian},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2605.00287},
  eprint = {2605.00287},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2605.00287},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Sequential Measurements as a Resource in Ancilla-Assisted Quantum Metrology
AU  - Koray Mentesoglu
AU  - Rahul Trivedi
AU  - Sara Mouradian
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2605.00287
UR  - https://arxiv.org/abs/2605.00287
AB  - We present a protocol for simultaneous estimation of both quadratures of a displacement channel on a quantum harmonic oscillator using a single ancilla qubit, without complex state preparation or adaptive control. The qubit is coupled to the quantum harmonic oscillator via controlled displacements of strength A and undergoes N rounds of measurement and reset, while the oscillator coherently accumulates the displacement signal. The non-commuting displacements imprint an order-dependent geometric phase at each round, giving a quantum Fisher information that scales as 𝒪(A^2 N^3). Although the measurement record space grows as 2^N, we show that exact likelihoods for any individual measurement record can be computed in 𝒪(N^2) time. With this, we show that measurement in the computational basis approximately saturates the quantum bound and maintains the 𝒪(A^2 N^3) scaling. Furthermore, the periodic information extraction makes the protocol robust to decoherence. Our results provide a framework for the design and analysis of sequential measurement in ancilla-assisted protocols.
ER  -

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