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HQ-NOM Report Summary

Project ID: 307370
Funded under: FP7-IDEAS-ERC
Country: France

Final Report Summary - HQ-NOM (Hybrid Quantum Nano-Optomechanics)

We developed novel techniques to probe ultra-weak forces by measuring their action on ultrasensitive nanomechanical probes in the form of suspended silicon carbide nanowires. Their vibrations in 2D could be optically readout using a tightly focussed laser beam, which permits using nanowires as vectorial force field sensors with sensitivities falling in the attoNewton range (/1s) at 300K. They then played a central role in project.
First we experimentally mapped the optomechanical interaction of the nanowire in a focused laser beam and analysed the impact of the force field gradients on the nanowire dynamics. A novel force sensing methodology based on the analysis of the nanowire dressing by the force under investigation was developed and validated by probing the electrostatic force field produced by a voltage biased tip.
We explored the nanowire dynamics in a rotational optical force field produced on the side of an optical waist. We reported on eigenmode orthogonality breaking, alteration of thermal noise and violation of the fluctuation dissipation relation. We also demonstrated noise reduction and opened novel connections with non-reciprocal coupling.
To improve the force sensing capacity and accelerate the measurement speed, we developed novel measurement strategies based on dynamically controlled multi-tone excitations. A proof of concept project was accepted, aiming at disseminating our ultrasensitive vectorial force probes to a larger audience.

We coupled a single NV spin qubit to the vibrations of a silicon carbide nanowire using a position dependent Zeeman effect produced by a strong magnetic field. We first explored the resolved sideband regime, a prerequisite for future dynamical applications and the spin locking on a RF tone. We then demonstrated the synchronization of the spin precession on the driven mechanical motion based on microwave dressing of the spin qubit, thus revealing a so-called phononic Mollow triplet, in analogy with the funding signature of quantum electrodynamics with interacting photons and atoms reproduced here with phonons and spins. We further investigated the impact of the Brownian motion on the spin qubit coherence and the possibility to protect the spin qubit using an additional coherent mechanical drive of the oscillator. Finally, by combining the ultrasensitive force sensing principle with the hybrid experiment, we engaged the exploration of spin-dependent forces, aiming a measuring mechanically the qubit state.

We then investigated an integrated version of the hybrid qubit-oscillator experiment, using a quantum dot embedded at the base of a movable photonic trumpet designed to maximize the photon out-coupling efficiency. The hybrid coupling proceeds through the strain modulation induce by the mechanical deformation of the oscillator, which leads to a frequency shift of the QDot resonance. We demonstrated the possibility to reach the ultra-strong coupling regime, when a single QDot excitation can displace the oscillator by more than its zero-point fluctuations.
To increase the force sensitivity of our probes and transpose the hybrid experiments down to ultralow temperatures, we internally developed a dilution fridge compatible with nano-optomechanics experiments: large stability, large working space, low vibrations, optical and microwave access. At the condition to operate with ultralow optical flux (picowatt range) we demonstrated the operation of nanowires as ultrasensitive scanning force probes giving access to unprecedented force sensitivities of 50 zN/sqrt(Hz) at 20 mK.

The ERC starting grant thus allowed to develop demanding experiments and permitted merging together an active group of researchers, engineers and technicians which will play a central role in the future scientific developments in the group.

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