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Millikelvin cooling of an optically trapped microsphere in vacuum

Nature Physics volume 7, pages 527530 (2011) | Download Citation

Abstract

Cooling of micromechanical resonators towards the quantum mechanical ground state in their centre-of-mass motion has advanced rapidly in recent years1,2,3,4,5,6,7,8. This work is an important step towards the creation of ‘Schrödinger cats’, quantum superpositions of macroscopic observables, and the study of their destruction by decoherence. Here we report optical trapping of glass microspheres in vacuum with high oscillation frequencies, and cooling of the centre-of-mass motion from room temperature to a minimum temperature of about 1.5 mK. This new system eliminates the physical contact inherent to clamped cantilevers, and can allow ground-state cooling from room temperature9,10,11,12,13,14,15. More importantly, the optical trap can be switched off, allowing a microsphere to undergo free-fall in vacuum after cooling15. This is ideal for studying the gravitational state reduction16,17,18,19, a manifestation of the apparent conflict between general relativity and quantum mechanics16,20. A cooled optically trapped object in vacuum can also be used to search for non-Newtonian gravity forces at small scales21, measure the impact of a single air molecule14 and even produce Schrödinger cats of living organisms9.

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Acknowledgements

We thank O. Romero-Isart for discussion of using a cooled microsphere to test objective reduction of the wavefunction models. We also thank D. Medellin and Z. Q. Yin for helpful discussions. M.G.R. acknowledges support from the Sid W. Richardson Foundation and the R. A. Welch Foundation, grant number F-1258. T.L. acknowledges support from the Lawrence C. Biedenharn Endowment for Excellence.

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Affiliations

  1. Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA

    • Tongcang Li
    • , Simon Kheifets
    •  & Mark G. Raizen

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Contributions

T.L. and M.G.R. designed the project. S.K. and T.L. carried out the experiment. All authors wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Mark G. Raizen.

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https://doi.org/10.1038/nphys1952

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