Ultra-coherent nanomechanical resonators via soft clamping and dissipation dilution

TL;DR

This paper presents a novel phononic bandgap design for nanomechanical resonators that achieves ultra-high quality factors and coherence times at room temperature, significantly reducing dissipation and noise.

Contribution

It introduces a new mode definition using phononic bandgap structures that isolates the resonator, achieving unprecedented Q-factors and coherence times at room temperature.

Findings

Mechanical Q>10^8 at 1 MHz

Highest Qf-products (>10^14 Hz) at room temperature

Coherence times comparable to optically trapped particles

Abstract

The small mass and high coherence of nanomechanical resonators render them the ultimate force probe, with applications ranging from biosensing and magnetic resonance force microscopy, to quantum optomechanics. A notorious challenge in these experiments is thermomechanical noise related to dissipation through internal or external loss channels. Here, we introduce a novel approach to defining nanomechanical modes, which simultaneously provides strong spatial confinement, full isolation from the substrate, and dilution of the resonator material's intrinsic dissipation by five orders of magnitude. It is based on a phononic bandgap structure that localises the mode, without imposing the boundary conditions of a rigid clamp. The reduced curvature in the highly tensioned silicon nitride resonator enables mechanical $Q>10^{8}$ at $ 1 \,\mathrm{MHz}$, yielding the highest mechanical $Qf$-products ($>10^{14}\,\mathrm{Hz}$) yet reported at room temperature. The corresponding coherence times approach those of optically trapped dielectric particles. Extrapolation to $4{.}2$ Kelvin predicts $\sim$quanta/ms heating rates, similar to trapped ions.