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Quantum-enhanced sensing of a mechanical oscillator



Katherine C. McCormick, Jonas Keller, Shaun C. Burd, David J. Wineland, Andrew C. Wilson, Dietrich Leibfried


The use of special quantum states in interferometry with bosons to achieve sensitivities below the limits established by classical-like coherent dates back decades and has enjoyed immense success since its inception. Squeezed states, number states, and cat states have been implemented on various platforms and all have demonstrated improved measurement precision over a coherent-state-based interferometer. Another state that ideally reaches the full interferometric sensitivity allowed by quantum mechanics is an equal superposition of two eigenstates with maximally different energies. We extend a technique to create number states up to n=100 and to generate superpositions of a harmonic oscillator ground state and a number state of the form |0>+|n> up to n=18 in the motion of a single trapped ion. While experimental imperfections prevent us from reaching the ideal Heisenberg limit, we observe enhanced sensitivity to changes in the oscillator frequency that initially increases linearly with n, with maximal value at n=12 where we observe 2.1(1) times higher sensitivity compared to an ideal measurement on a coherent state with the same average occupation. The quantum advantage from using number-state superpositions can be leveraged towards precision measurements on any harmonic oscillator system; here it enables us to track the average fractional frequency of oscillation of a single trapped ion to approximately 2.6*10^-6} in 5 s. We demonstrate that such measurements enable improved characterization of imperfections and noise on trapping potentials, which can lead to motional decoherence, an important source of error in quantum information processing with trapped ions.


harmonic oscillator, quantum control, quantum mechanics, quantum sensing, harmonic oscillator


McCormick, K. , Keller, J. , Burd, S. , Wineland, D. , Wilson, A. and Leibfried, D. (2019), Quantum-enhanced sensing of a mechanical oscillator, Nature, [online],, (Accessed June 21, 2024)


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Created July 21, 2019, Updated October 12, 2021