Experiments with nanomechanical oscillators are now addressing what were once purely theoretical questions: the initialization, control, and readout of the quantum state of a mechanical oscillator. Researchers are able both to initialize the fundamental vibrational mode of a mechanical resonator into its ground state and even to produce nonclassical coherent states of motion. The prospects are bright for exploiting these achievements to produce mechanical sensors whose sensitivity is limited only by quantum effects or to use a mechanical state to encode quantum information. The ability to initialize and observe the quantization of mechanical motion is particularly noteworthy not only from a fundamental point of view but also because mechanical oscillators are excellent transducers. By functionalizing a resonator with an electrode, magnet, or mirror, mechanical motion can be transformed into the modulation of electric, magnetic, or optical fields. The ease of this process has inspired proposals to use mechanical resonators as quantum buses, mediating interactions between different quantum systems. Furthermore, such couplings have now been demonstrated in a variety of quantum systems including optical and microwave cavities, superconducting devices, laser-cooled atoms, quantum dots, and nitrogen vacancy centers in diamond. In most cases, however, the functionalization of the mechanical oscillator with a coupling element competes with the requirement of a small resonator mass, necessary for achieving a high coupling strength. Moreover, the functionalization process often adds additional paths of dissipation and decoherence, reducing the lifetime of the coupled quantum system, or “hybrid” system.
In collaborations with external colleagues and Prof. Warburton here in Basel, we have demonstrated the coupling of NW mechanical oscillators with optically addressable QDs [1,2]. We now aim to integrate NW cantilevers into high-finesse optical cavities , which can improve the read-out of both the mechanical motion and of the photons emitted by embedded QDs. Moreover, such a cavity can strongly couple NW motion and QD excitons to the cavity light field, realizing a tri-partite hybrid system. Such a hybrid system can significantly enhance optical cooling and could allow for the observation and utilization of quantum states of motion . We will continue to work on a variety of hybrid systems, including new work with Prof. Stefan Willitsch (Chemistry) on coupling a NW to a trapped ion .
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