A SQUID based read-out of sub-attoNewton force sensor operating at millikelvin temperatures
msra(2010)
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.
MoreTranslated text
Key words
magnetic particle,force sensor,magnetic resonance force microscopy,quantum effect,mechanical systems
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