Ultra-coherent nanomechanical resonators based on inverse design

Engineered micro- and nanomechanical resonators with ultra-low dissipation constitute the ideal systems for applications ranging from high-precision sensing such as magnetic resonance force microscopy, to quantum transduction between disparate quantum systems. Traditionally, the improvement of the resonator's performance - often quantified by its Qf product (where Q is quality factor and f is frequency) - through nanomechanical engineering such as dissipation dilution and strain engineering, has been driven by human intuition and insight. Such an approach is inefficient and leaves aside a plethora of unexplored mechanical designs that potentially achieve better performance. Here, we use a computer-aided inverse design approach known as topology optimization to structurally design mechanical resonators with optimal performance of the fundamental mechanical mode. Using the outcomes of this approach, we fabricate and characterize ultra-coherent nanomechanical resonators with record-high Qf products, entering a quantum coherent regime where coherent oscillations are observed at room temperature. Further refinements to the model describing the mechanical system are likely to improve the Qf product even more. The proposed approach - which can be also used to improve phononic crystal and coupled-mode resonators - opens up a new paradigm for designing ultra-coherent micro- and nanomechanical resonators for cutting-edge technology, enabling e.g. novel experiments in fundamental physics (e.g. search for dark matter and quantum nature of gravity) and extreme sensing of magnetic fields, electric fields and mass with unprecedented sensitivities at room temperature.