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Quantum Nano Optomechanics

Final Report Summary - QNAO (Quantum Nano Optomechanics)

The objectives of the project were to develop new techniques for imaging the motion of nanomechanical oscillators, in order to realize ultrasensitive force probes for investigating the coupling to a single quantum system such as a single spin or a quantum dot.

The Reintegration Grant has allowed the applicant to efficiently develop its own research activities in the emerging field of hybrid nanomechanics within the host institution. As originally planned, two main directions were simultaneously and successfully developed, in the fields of nano-optomechanics and hybrid nanomechanical systems.

The first important direction concerns the demonstration of the possibility of optically probing the nanomotion of sub-wavelength oscillators with sensitivities at the standard quantum limit. By placing the nanoresonator in a strongly focussed light field and measuring the transmitted scattered light, it is possible to probe with an extreme signal to noise the displacement of nanowires in a cavity-free setting. The ultralow mass of the nanoresonators employed allowed demonstrating force measurements with sensitivities at the attonewton level in a room temperature experiment. This allowed imaging the spatial vectorial topography of the optical back action exerted by the light beam onto the nanoresonator. In particular the applicant could directly observe its non conservative nature and analyze the consequence of the optical force field vorticity onto the resonator dynamics, which leads to a new class of strong coupling regime between oscillation modes of the resonator.

The second important result concerns the first realization of a hybrid spin nanomechanical system made of a single NV spin qubit attached to the extremity of a silicon carbide nanowire and the demonstration that the nanowire nanomotion is imprinted on the spin state and was revealed by spin spectroscopy. This work represents the starting point of the research into which the applicant is engaged, aiming at investigating the coupling in the reversed direction: measuring mechanically the spin state and observing entanglement between the spin state and the oscillator position.
The applicant has also established strong connections with local researchers in the host institution around its research thematic. In particular quantum dots inserted in nanomechanical oscillators have been employed for exploring hybrid system undergoing strain coupling.

Finally, a study was initiated in order to explore more complex spin manipulation protocols in hybrid systems. This allowed demonstrating the possibility to synchronize the spin dynamics onto the nanomechanical motion by dressing the spin with a resonant microwave field. This mechanism which was investigated in detail is extremely promising for the rest of the project since the spin gets automatically locked onto the resonator, which allows advanced measurement protocols in hybrid spino-mechanical systems.