Strong gate coupling of high-Q nanomechanical resonators

TL;DR

This paper demonstrates strong electrical coupling of high-quality nanomechanical resonators to microwave cavities, achieving low phonon numbers and high Q-factors at millikelvin temperatures, advancing quantum-limited detection.

Contribution

It introduces a method to achieve large cavity coupling energy in metallic nanomechanical resonators using focused ion beam fabrication, with high Q-factors at very low temperatures.

Findings

Achieved cavity coupling energy up to 1 MHz/nm.

Recorded a quality factor of ~3 x 10^5 at 25 mK.

Measured linear dissipation proportional to temperature between 0.2K and 2K.

Abstract

The detection of mechanical vibrations near the quantum limit is a formidable challenge since the displacement becomes vanishingly small when the number of phonon quanta tends towards zero. An interesting setup for on-chip nanomechanical resonators is that of coupling them to electrical microwave cavities for detection and manipulation. Here we show how to achieve a large cavity coupling energy of up to (2 \pi) 1 MHz/nm for metallic beam resonators at tens of MHz. We used focused ion beam (FIB) cutting to produce uniform slits down to 10 nm, separating patterned resonators from their gate electrodes, in suspended aluminum films. We measured the thermomechanical vibrations down to a temperature of 25 mK, and we obtained a low number of about twenty phonons at the equilibrium bath temperature. The mechanical properties of Al were excellent after FIB cutting and we recorded a quality factor of Q ~ 3 x 10^5 for a 67 MHz resonator at a temperature of 25 mK. Between 0.2K and 2K we find that the dissipation is linearly proportional to the temperature.