在毫开尔文温度下工作的基于PDKEEPAAA的sub-attoNewton力传感器的读出
A SQUID based read-out of sub-attoNewton force sensor operating at millikelvin temperatures
摘要：
越来越多的实验需要使用超灵敏的纳米机械谐振器。相关的例子是机械系统中量子效应的研究[1]或磁共振力显微镜（MRFM）中极小力的检测[2]。机械谐振器的力灵敏度通常受到热波动的限制，这需要能够在超低温下操作的检测方法。通常使用的干涉技术，尽管其出色的灵敏度，可能不是一个最佳的选择，在毫开尔文温度，因为不必要的谐振器加热光子吸收引起的。虽然基于微波腔[3] [4] [5]的替代检测技术已显示在超低温下表现更好，但这些技术仍然存在检测灵敏度随着功率输入降低而降低的事实。在这里，我们提出了一种测量方法的基础上检测，通过超导量子干涉器件（SQUID），在线圈中感应的磁通量的变化的磁性粒子附着到谐振器的运动。这种检测方案避免了谐振器的直接加热，因为它不涉及将光学或微波光子反射到谐振器。通过将超软硅谐振器冷却至25 mK，我们在1 Hz带宽内实现了0.5 aN的力噪声。我们相信这种检测技术原则上甚至可以在亚毫开尔文温度下使用。此外，它可以用来提高灵敏度的MRFM实验，旨在在原子分辨率的三维成像。
英文摘要：
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.
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