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Quantum ground state and single-phonon control of a mechanical resonator


Quantum mechanics provides a highly accurate description of a wide variety of physical systems. However, a demonstration that quantum mechanics applies equally to macroscopic mechanical systems has been a long-standing challenge, hindered by the difficulty of cooling a mechanical mode to its quantum ground state. The temperatures required are typically far below those attainable with standard cryogenic methods, so significant effort has been devoted to developing alternative cooling techniques. Once in the ground state, quantum-limited measurements must then be demonstrated. Here, using conventional cryogenic refrigeration, we show that we can cool a mechanical mode to its quantum ground state by using a microwave-frequency mechanical oscillator—a ‘quantum drum’—coupled to a quantum bit, which is used to measure the quantum state of the resonator. We further show that we can controllably create single quantum excitations (phonons) in the resonator, thus taking the first steps to complete quantum control of a mechanical system.

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Figure 1: Dilatational resonator.
Figure 2: Coupled qubit–resonator.
Figure 3: Resonator spectroscopy.
Figure 4: Qubit thermometry of resonator.
Figure 5: Qubit–resonator swap oscillations.
Figure 6: Resonator energy decay and dephasing times.
Figure 7: Resonator coherent state.


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We would like to thank M. Geller for numerous conversations and A. Berube for assistance with resonator fabrication and measurements. This work was supported by the US National Science Foundation (NSF) under grant DMR-0605818 and by the Intelligence Advanced Research Projects Activity under grant W911NF-04-1-0204. Devices were made at the University of California, Santa Barbara, Nanofabrication Facility, which is part of the NSF-funded US National Nanotechnology Infrastructure Network.

Author Contributions A.D.O’C. fabricated the devices and performed the measurements, M.H. providing measurement assistance. A.N.C., A.D.O’C. and J.M.M. conceived and designed the experiment. All authors contributed to providing experimental support and writing the manuscript.

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Corresponding author

Correspondence to A. N. Cleland.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This Supplementary Information file comprises: (I) Methods - Mechanical Resonator Fabrication; (II) Methods - Qubit-Mechancial Resonator Fabrication; (III) Verification of Mechancial Nature of Resonance; (IV) Qubit Measurement; (V) Qubit Characterization; (VI) Simulations; (VII) Classical Circuit Analyses; and includes Supplementary Figures 1-3 with Legends and Supplementary References. (PDF 709 kb)

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O’Connell, A., Hofheinz, M., Ansmann, M. et al. Quantum ground state and single-phonon control of a mechanical resonator. Nature 464, 697–703 (2010).

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