Nano- and micromechanical resonators, with their high coherence and low mass, serve as extremely good sensors of small forces and particles. They are especially powerful in combination with optical laser fields, which can measure mechanical motion down to the level where quantum mechanics is needed to describe it. The performance of mechanical quantum sensors, and in fact our ability to measure their displacement, is however limited by fundamental concepts: Heisenberg’s uncertainty principle dictates the smallest vibration that can be resolved. And time-reversal symmetry bounds the measurement rate of a sensor. In this project, we challenge both limits – evading them by making nanomechanical resonators interact strongly with temporally controlled and nano-confined light fields. The experiments we perform will project a macroscopic mechanical object in a pure quantum state, through the mere act of performing a strong measurement. We aim to show that such measurements can entangle the object’s internal degrees of freedom, and can be used to boost metrology performance. By breaking time-reversal symmetry through optical control, we seek to enhance the sensitivity of mechanical force sensors. The project investigates whether the measurement interaction can be employed to coherently convert optical to mechanical states, and to manipulate optical signals down to the single-photon level. The realization of these goals are expected to advance mechanical quantum sensing, create coherent interfaces for quantum communication, and establish novel ways to control light and motion at the quantum level. Moreover, we will gain a new fundamental understanding of metrology and sensing performance in basic systems that transcend the mechanical domain. Finally, these foundational experiments will bring intriguing quantum effects in full view in ‘tangible’ objects, and test whether they can in fact exist at such macroscopic scales. During the course of the project, we have established the experimental and theoretical foundations required to address these objectives, including strong pulsed quantum measurements of mechanical motion, the generation of mechanical squeezing, and the realization of multimode nonreciprocal networks that control the flow of noise and information through engineered interactions. These advances confirm the feasibility of the proposed approach and the ability of time-modulated strong optomechanical interactions to enable new measurement and control capabilities in quantum optomechanical systems and sensor technologies operating at fundamental limits.
