Quantum jumps of sound.

Makihara, Takuma; Szakiel, Erik; Maksymowych, Matthew P; Hitchcock, Oliver A; Pezeshki, Kaveh; Gruenke-Freudenstein, Rachel G; Pendharkar, Mihir; Harvey, Shannon P et al. · Science · 2026

basic_science · Level V

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Abstract

Quantum mechanics predicts that a vibrating object's energy comes in discrete packets, yet no measurement of its position reveals this discreteness. Resolving individual energy levels requires a qualitatively different measurement, one coupling to the resonator's energy rather than its displacement. We use a superconducting qubit dispersively coupled to a nanomechanical resonator to perform repeated quantum nondemolition measurements of the phonon number. An aligned transfer-print technique integrating the qubit and resonator yields a mechanical lifetime of [Formula: see text] milliseconds and a dispersive shift of [Formula: see text] kilohertz per phonon. We heralded single-phonon states with 85% fidelity and observed quantum jumps between the resonator's first excited state and ground state. These discontinuous transitions are a striking manifestation of quantum mechanics in a massive, vibrating object.