Addressing the first challenge we have realized nanomechanical resonators with unprecedented mechanical coherence. They are based on a novel method called soft-clamping. It relies on the combination of phononic crystals with strain-based dissipation dilution. This groundbreaking invention, made within this project, relaxes requirements for quantum-coherent opto- and electro-mechanical coupling. It may even lead to new applications in force-sensing, nano-imaging, and gravitational astronomy.
By coupling soft-clamped membrane resonators to an optical field we could realize optical measurement of motion close to the standard quantum limit (SQL). Based on such precise measurements, we could, for the first time, control the motional quantum state of the membrane using quantum feedback, and cool it to its ground state. Exploiting quantum correlations born in the measurement process, we could also beat the SQL for both position and force measurements.
Furthermore, were could generate quantum correlations between two laser fields of different wavelength, mediated by their interaction with a single membrane resonator. We could show that the light fields emerging from the interaction are indeed entangled. This hallmark of quantum physics signals the potential for mechanically-mediated interactions for quantum information processing.
Addressing the second challenge, we have realized electromechanical systems with superconducting microwave resonators capacitively coupled to soft-clamped, metallized membranes. The system’s high coherence enables a strong quantum cooperativity, and thereby ground state cooling of the mechanical system via microwave backaction.
Finally, we have performed theoretical studies to determine relevant figures of merit for quantum transducers. An important outcome is a detailed analysis of the importance of transfer efficiency and added noise, depending on the task of the transducer. Further work has made the project’s topic accessible to a broader audience, by taking a microwave engineering perspective, as well as giving a broader overview of nano-electro-optomechanical systems.
