Ultrasensitive force measurements at the quantum/classical interface

Orateur : Benjamin PIGEAU

The principle of atomic force microscopy, converting a physical quantity into a force using a sensitive mechanical transducer, has now proven its efficiency and was applied to various systems. The recent revolution in this field is driven by the synthesis or nano fabrication of nano reosna tors. The drastic reduction of the size/mass of these mechanical oscillators allows to reach force sensitivities in the atto-Newton range. I will show how this opportunity can be applied to study quantum phenomena. An hybrid system consisting in a mechanical oscillator coupled to a purely quantum object is indeed a powerful tool to study the quantum to macroscopic world interface. This is a unique route toward the creation of counter intuitive non classical states of motion. The emblematic signatures of quantum electrodynamics (QED), such as Rabi oscillations of the quantum system population and Mollow triplet physics, are expected to arise from the hybrid coupling [1]. The novelty is the macroscopic nature of the probe field, the visible or microwave photons being replaced by the oscillator phonon field. Here we investigate the dynamics of a SiC nanowire coupled to a nano-diamond hosting a single Nitrogen Vacancy defect [2]. The SiC wires have intrinsically large oscillation amplitudes at high frequency and exhibit two orthogonal nearly degenerated modes. Regarding their ultra low masses they are very accurate vectorial force sensors. The NV center contains a single electronic (S=1) spin that can be manipulated and readout using laser light. Similarly to a Stern-Gerlach experiment, the Zeeman energy of the spin is coupled to the oscillator position when immersed in a strong magnetic field gradient. The spin energy is therefore parametrically modulated at the mechanical frequency. It will be evidenced that this system has the potential to enter the strong coupling regime [1,2]. As a result of this QED like interaction a phonon-dressed Mollow triplet is observed in the Rabi frequency of the spin [3]. Perspectives upon the measurement of the single spin back-action on the mechanical oscillator, especially in the Mollow triplet regime, will be given. Finally I will show how the vectorial force sensing provided by these nanowires can be usefull to measure the dynamics of spin ensembles.

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