Strong coupling is an important requirement to achieve coherent quantum control over a physical system. So far, this has been demonstrated only between microscopic quantum systems, such as atoms and photons (in the context of cavity quantum electrodynamics) or solid state qubits and photons. We have recently observed optomechanical normal mode splitting, which provides unambiguous evidence for strong coupling of cavity photons to a mechanical resonator. This paves the way towards full quantum optical control of nano- and micromechanical devices and will be essential for future preparation of mechanical quantum states such as squeezed or entangled states and also for using mechanical resonators in the context of quantum information processing, for example, as quantum transducers.

[1] S. Gröblacher, K. Hammerer, M. R. Vanner, M. Aspelmeyer; Nature 460, 724-727 (2009)

Preparing and manipulating quantum states of mechanical resonators is a highly interdisciplinary undertaking that now receives enormous interest for its far-reaching potential in fundamental and applied science. We have achieved a new world-record for micromechanical laser-cooling by demonstrating a micro-optomechanical resonator that is laser cooled to a level of 30 thermal quanta. This is equivalent to the best nanomechanical devices, however, with a mass more than four orders of magnitude larger (43 ng versus 1 pg) and at more than two orders of magnitude higher environment temperature (5 K versus 30 mK). These results pave the way for the preparation of 100µ scale objects in the quantum regime. This work has been performed in collaboration with the group by Keith Schwab at Cornell University.

[2] S. Gröblacher, J. B. Hertzberg, M. R. Vanner, G. D. Cole, S. Gigan, K. C. Schwab, M. Aspelmeyer; Nature Physics 5, 485-488 (2009), published online 07 June 2009 (doi:10.1038/nphys1301) [arxiv:0901.1801 [quant-ph] (2009)]

We have suggested a new scheme to interface nanomechanical systems via an optical quantum bus to atomic ensembles. This allows, in particular, for a quantum nondemolition Bell measurement, projecting the coupled system, atomic-ensemble-nanomechanical resonator, into an entangled EPR state. Simulations suggest that the entanglement is observable even for nanoresonators initially well above their ground states and can be utilized for teleportation of states from an atomic ensemble to the mechanical system. This work has been performed in collaboration with colleagues from the University of Innsbruck and the Nils Bohr Institute in Copenhagen.

[3] K. Hammerer, M. Aspelmeyer, E. S. Polzik, and P. Zoller; Phys. Rev. Lett. 102, 020501 (2009)