A SQUID based read-out of sub-attoNewton force sensor operating at millikelvin temperatures

TL;DR

This paper introduces a SQUID-based magnetic flux detection method for ultrasensitive nanomechanical resonators operating at millikelvin temperatures, achieving record force sensitivity without heating the resonator, with potential applications in atomic-resolution imaging.

Contribution

The paper presents a novel SQUID-based detection scheme for nanomechanical resonators that operates effectively at ultralow temperatures, avoiding heating issues of traditional optical or microwave methods.

Findings

Achieved a force noise of 0.5 aN at 25 mK in a 1 Hz bandwidth.

Demonstrated the method's potential for sub-millikelvin operation.

Improved sensitivity for magnetic resonance force microscopy (MRFM).

Abstract

An increasing number of experiments require the use of ultrasensitive nanomechanical resonators. Relevant examples are the investigation of quantum effects in mechanical systems [1] or the detection of exceedingly small forces as in Magnetic Resonance Force Microscopy (MRFM) [2]. The force sensitivity of a mechanical resonator is typically limited by thermal fluctuations, which calls for detection methods capable of operating at ultralow temperature. Commonly used interferometric techniques, despite their excellent sensitivity, may not be an optimal choice at millikelvin temperatures, because of unwanted resonator heating caused by photon absorption. Although alternative detection techniques based on microwave cavities [3] [4] [5] have shown to perform better at ultralow temperature, these techniques still suffer from the fact that the detection sensitivity decreases as the power input is decreased. Here, we present a measurement approach based on the detection, through a Superconducting Quantum Interference Device (SQUID), of the change of magnetic flux induced in a coil by the motion of a magnetic particle attached to a resonator. This detection scheme avoids direct heating of the resonator, as it does not involve reflecting optical or microwave photons to the resonator. By cooling an ultrasoft silicon resonator to 25 mK, we achieve a force noise of 0.5 aN in a 1 Hz bandwidth. We believe this detection technique can in principle be used even at sub-millikelvin temperatures. Furthermore, it could be used to improve the sensitivity of MRFM experiments, which aim at three dimensional imaging at atomic resolution.