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Quantum non-Gaussian coherences of an oscillating atom

A. Kovalenko1,*, L. Lachman1,*, T. Pham2, K. Singh1, O. Číp2, J. Fiurášek1, L. Slodička1, and R. Filip1

  • *These authors contributed equally to this work.
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Phys. Rev. Research 7, 033075 – Published 18 July, 2025

DOI: https://doi.org/10.1103/5nxx-r97j

Abstract

Quantum coherence between energy eigenstates of harmonic oscillators is essential for quantum physics. Even the most elementary binary superpositions of the ground and the higher eigenstate are highly required for quantum sensing, thermodynamics, and computing. We derive upper bounds for quantum coherences achieved by classical and Gaussian states and operations and, subsequently, obtain a hierarchy of the thresholds for the off-diagonal elements necessary to reach genuine quantum non-Gaussian coherences. The presented analysis demonstrates that certification based solely on estimation of coherences can cover the quantum non-Gaussian states, which are undetectable by the criteria based solely on the estimation of the corresponding state populations. We experimentally demonstrate the unambiguous observation of quantum non-Gaussian coherences in mechanical vibrations of a single calcium ion up to the superposition of zero and six phonons. The analysis of the robustness with respect to pure dephasing in a motional Ramsey experiment demonstrates the feasibility of their storage for up to more than 20 ms for superpositions with a large energy difference of participating number states. The presented observations prove that atomic oscillations go deeply into a diverse area of discrete quantum non-Gaussian coherent phenomena critical for their applications.

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Phys. Rev. Research 7, 033075– Published 18 July, 2025
  • Received 6 February 2024
  • Accepted 13 June 2025
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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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