Nonlinear nanomechanical resonators approaching the quantum ground state

• Published in: Nature physics Vol. 19; no. 9; pp. 1340 - 1344
• Main Authors: Samanta, C., De Bonis, S. L., Møller, C. B., Tormo-Queralt, R., Yang, W., Urgell, C., Stamenic, B., Thibeault, B., Jin, Y., Czaplewski, D. A., Pistolesi, F., Bachtold, A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2023; Nature Publishing Group; Nature Publishing Group (NPG)
• Subjects: 639/766/119; 639/925/927/359; Anharmonicity; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Coupling; Electron tunneling; Electrons; Graphene; Ground state; MATERIALS SCIENCE; Mathematical and Computational Physics; Molecular; Nonlinearity; Optical and Plasma Physics; Physics; Physics and Astronomy; Quantum dots; Qubits (quantum computing); Resonators; Simulators; Single electrons; Temperature; Theoretical; Thermal energy; Vibration; carbon nanotube NEMS quantum technologies
• ISSN: 1745-2473; 1745-2481; 1476-4636
• DOI: 10.1038/s41567-023-02065-9

It is an open question whether mechanical resonators can be made nonlinear with vibrations approaching the quantum ground state. This requires the engineering of a mechanical nonlinearity far beyond what has been realized so far. Here we discover a mechanism to boost the Duffing nonlinearity by coupling the vibrations of a nanotube resonator to single-electron tunnelling and by operating the system in the ultrastrong-coupling regime. We find that thermal vibrations become highly nonlinear when lowering the temperature. The average vibration amplitude at the lowest temperature is 13 times the zero-point motion, with approximately 42% of the thermal energy stored in the anharmonic part of the potential. Our work may enable the realization of mechanical Schrödinger cat states, mechanical qubits and quantum simulators emulating the electron–phonon coupling. Although mechanical resonators are routinely cooled to their quantum ground state, it has remained unclear if sizable nonlinearities could persist there. Experiments in the ultrastrong-coupling regime now show that this is possible.