Coherent coupling and non-destructive measurement of trapped-ion mechanical oscillators

• Published in: Nature physics Vol. 20; no. 10; pp. 1636 - 1641
• Main Authors: Hou, Pan-Yu, Wu, Jenny J., Erickson, Stephen D., Cole, Daniel C., Zarantonello, Giorgio, Brandt, Adam D., Geller, Shawn, Kwiatkowski, Alex, Glancy, Scott, Knill, Emanuel, Wilson, Andrew C., Slichter, Daniel H., Leibfried, Dietrich
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2024; Nature Publishing Group
• Subjects: 639/766/36/1121; 639/766/483/3925; 639/766/483/481; Accuracy; Atomic; Classical and Continuum Physics; Coherence; Complex Systems; Condensed Matter Physics; Coupling; Data processing; Electric fields; Electric potential; Electromagnetic fields; Error correction; Error correction & detection; Harmonic control; Harmonic oscillators; Hilbert space; Information processing; Ion motion; Ions; Mathematical and Computational Physics; Mechanical oscillators; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Quantum computing; Quantum entanglement; Quantum phenomena; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-024-02585-y

Precise quantum control and measurement of several harmonic oscillators, such as the modes of the electromagnetic field in a cavity or of mechanical motion, are key for their use as quantum platforms. The motional modes of trapped ions can be individually controlled and have good coherence properties. However, achieving high-fidelity two-mode operations and non-destructive measurements of the motional state has been challenging. Here we demonstrate the coherent exchange of single motional quanta between spectrally separated harmonic motional modes of a trapped-ion crystal. The timing, strength, and phase of the coupling are controlled through an oscillating electric potential with suitable spatial variation. Coupling rates that are much larger than decoherence rates enable demonstrations of high-fidelity quantum state transfer and beam-splitter operations, entanglement of motional modes, and Hong–Ou–Mandel-type interference. Additionally, we use the motional coupling to enable repeated non-destructive projective measurement of a trapped-ion motional state. Our work enhances the suitability of trapped-ion motion for continuous-variable quantum computing and error correction and may provide opportunities to improve the performance of motional cooling and motion-mediated entangling interactions. A lack of non-destructive measurements and difficulty in tuning direct coupling between motional modes limits quantum information processing with trapped ions. Both features have now been achieved in an ion crystal using oscillating electric fields.