Ground state cooling and quantum backaction of a mechanical oscillator - GSC
Final Report Abstract
Cavity optomechanics is a new research field that explores the coupling of optical and mechanical degrees of freedom. In the past five years the field has experienced a rapid growth due to the advances in fabricating nanomechanical oscillators coupled to optical degrees of freedom. Within this setting, our laboratory has implemented optomechanical transducers to sense the motion of micro- and nanomechanical oscillators. Silica toroidal microresonators were used lo measure the displacements of both, a silicon nitride nanomechanical beam oscillator - by placing the latter inlo the near field of the toroids' optical mode - and, in a different set of experiments, the micromechanical modes of the toroids themselves. In both cases, the imprecisison of the position measurement is limited only by the quantum noise of the light employed. We could show that, in principle, this imprecision is low enough to detect the quantum-mechanical zero-point fluctuations of the position of the measured oscillator, an unprecedented result. At room temperature, the quantum mechanical zero-point fluctuations of the oscillators' position are masked by its much larger random thermal agitation corresponding to the Brownian motion of the microscopic constituents of the oscillator. In our earlier work with optomechanical systems, we have already demonstrated that this random motion can be cooled by the aid of low-noise lasers. Theoretical analysis has also suggested that it is in principle possible to laser-cool nano- and micromechanical oscillators to their quantum ground state in this fashion. Experimenls have however proven cryogenic pre-cooling necessary. Only in this case can laser cooling maintain the strong non-equilibrium between the mechanical oscillator and its much hotter environment. Using a buffer-gas 4He cryostat for pre-cooling, we have been able to cool a micromechanical oscillator close to the quantum ground state, with a remaining occupation of only 60 quanta. In the same experiment, we could demonstrate that silica microtoroids constitute also near-ideal displacement transducers in the sense of quantum measurement theory: An experimental bound could be put on the amount of quantum backaction (perturbation of the oscillator motion) induced by the measurement process. We could conclude that the measurement satisfies the Heisenberg uncertainty limit - expressed here as an imprecision-backaction-product - to within a factor of 100. This is the closest experimentally demonstrated approach for any measurement of mechanical displacements.
Publications
- "Cavity Optomechanics: Back-Action at the Mesoscale". Science 321, 1172-1176 (2008)
T. J. Kippenberg and K. J. Vahala
- "Ultralow-dissipation optomechanical resonators on a chip". Nature Photonics 2, 627-633 (2008)
G. Anetsberger, R. Riviere, A. Schliesser, O. Arcizet, T. J. Kippenberg
- "Cryogenic properties of optomechanical silica microcavities". Physical Review A 80, 021803 (2009)
O. Arcizet, R. Rivifere, A. Schliesser, G. Anetsberger, and T. J. Kippenberg
- "Near-field cavity optomechanics with nanomechanical oscillators". Nature Physics 5, 909-914 (2009)
G. Anetsberger, O. Arcizet, Q. P. Unterreithmeier, R. Riviere, A. Schliesser, E. Weig, J. P. Kotthaus, and T. J. Kippenberg
- "Resolvedsideband cooling and position measurement of a micromechanical oscillator close to the Heisenberg uncertainty limit.". Nature Physics 5, 509-511 (2009)
A. Schliesser, O. Arcizet, R. Riviere, G. Anetsberger, and T. J. Kippenberg
- "Cavity optomechanics wilh silica microresonators". In: "Advances in atomic, molecular and optical physics," edited by E. Arimondo, P. Berman and C. C. Lin (Elsevier, 2010)
A. Schliesser and T. J. Kippenberg
- "Cavity optomechanics with ultra-high Q crystalline micro-resonators". Physical Review A 82, 031804 (2010)
J. Hofer, A. Schliesser, and T. J. Kippenberg
