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Register a new userAn analytical model for the detection of levitated nanoparticles in optomechanics
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Interferometric position detection of levitated particles is crucial for the centre-of-mass (CM) motion cooling and manipulation of levitated particles. In combination with balanced detection and feedback cooling, this system has provided picometer scale position sensitivity, zeptonewton force detection, and sub-millikelvin CM temperatures. In this article, we develop an analytical model of this detection system and compare its performance with experimental results allowing us to explain the presence of spurious frequencies in the spectra.
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Oscillators based on levitated particles are promising for the development of ultrasensitive force detectors. The theoretical performance of levitated nanomechanical sensors is usually characterized by the so-called thermal noise limit force detection sensitivity, which does not exhibit spectral specificity in practical measurements. To characterize the actual detection performance, we propose a method for the force detection sensitivity calibration of a levitated nanomechanical sensor based on the harmonic Coulomb force. Utilizing the measured transfer function, we obtained the force detection sensitivity spectrum from the position spectrum. Although the thermal noise limit force detection sensitivity of the system reached $rmleft( {4.39 pm 0.62} right) times {10^{ - 20}} N/H{z^{1/2}}$ at $rm{2.4times10^{-6} mbar}$ with feedback cooling, the measured sensitivity away from the resonance was of the order of $rm10^{-17} N/Hz^{1/2}$ based on the existing detection noise level. The calibration method established in our study is applicable to the performance evaluation of any optical levitation system for high-sensitivity force measurements.
Nanomechanical resonators are widely operated as force and mass sensors with sensitivities in the zepto-Newton and yocto-gram regime, respectively. Their accuracy, however, is usually undermined by high uncertainties in the effective mass of the system, whose estimation is a non-trivial task. This critical issue can be addressed in levitodynamics, where the nanoresonator typically consists of a single silica nanoparticle of well-defined mass. Yet, current methods assess the mass of the levitated nanoparticles with uncertainties up to a few tens of percent, therefore preventing to achieve unprecedented sensing performances. Here, we present a novel measurement protocol that uses the electrical field from a surrounding plate capacitor to directly drive a charged optically levitated particle in moderate vacuum. The developed technique estimates the mass within a statistical error below 1% and a systematic error of 2%, and paves the way toward more reliable sensing and metrology applications of levitodynamics systems.
We describe the measurement of the secular motion of a levitated nanoparticle in a Paul trap with a CMOS camera. This simple method enables us to reach signal-to-noise ratios as good as 10$^{6}$ with a displacement sensitivity better than 10$^{-16},m^{2}$/Hz. This method can be used to extract trap parameters as well as the properties of the levitated particles. We demonstrate continuous monitoring of the particle dynamics on timescales of the order of weeks. We show that by using the improvement given by super-resolution imaging, a significant reduction in the noise floor can be attained, with an increase in the bandwidth of the force sensitivity. This approach represents a competitive alternative to standard optical detection for a range of low frequency oscillators where low optical powers are required
Atomic force microscopy (AFM) has been constantly supporting nanosciences and nanotechnologies for over 30 years, being present in many fields from condensed matter physics to biology. It enables measuring very weak forces at the nanoscale, thus elucidating interactions at play in fundamental processes. Here we leverage the combined benefits of micro/nanoelectromechanical systems and cavity optomechanics to fabricate a sensor for dynamic mode AFM at a frequency above 100 MHz. This is two decades above the fastest commercial AFM probes, suggesting opportunity for measuring forces at timescales unexplored so far. The fabrication is achieved using very-large scale integration technologies inherited from photonic silicon circuits. The probes ring optomechanical cavity is coupled to a 1.55 um laser light and features a 130 MHz mechanical resonance mode with a quality factor of 900 in air. A limit of detection in displacement of 3.10-16 m/sqrt(Hz) is obtained, enabling the detection of the Brownian motion of the probe and paving the way for force sensing experiments in the dynamic mode with a working vibration amplitude in the picometer range. Inserted in a custom AFM instrument embodiment, this optomechanical sensor demonstrates the capacity to perform force-distance measurements and to maintain a constant interaction strength between tip and sample, an essential requirement for AFM applications. Experiments show indeed a stable closed-loop operation with a setpoint of 4 nN/nm for an unprecedented sub-picometer vibration amplitude, where the tip-sample interaction is mediated by a stretched water meniscus.
Torque sensors such as the torsion balance enabled the first determination of the gravitational constant by Cavendish and the discovery of Coulombs law. Torque sensors are also widely used in studying small-scale magnetism, the Casimir effect, and other applications. Great effort has been made to improve the torque detection sensitivity by nanofabrication and cryogenic cooling. The most sensitive nanofabricated torque sensor has achieved a remarkable sensitivity of $10^{-24} rm{Nm}/sqrt{rm{Hz}}$ at millikelvin temperatures in a dilution refrigerator. Here we dramatically improve the torque detection sensitivity by developing an ultrasensitive torque sensor with an optically levitated nanorotor in vacuum. We measure a torque as small as $(1.2 pm 0.5) times 10^{-27} rm{Nm}$ in 100 seconds at room temperature. Our system does not require complex nanofabrication or cryogenic cooling. Moreover, we drive a nanoparticle to rotate at a record high speed beyond 5 GHz (300 billion rpm). Our calculations show that this system will be able to detect the long-sought vacuum friction near a surface under realistic conditions. The optically levitated nanorotor will also have applications in studying nanoscale magnetism and quantum geometric phase.
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