Observation of radiation torque shot noise on an optically levitated nanodumbbell

Ultrasensitive torque detection with an optically levitated nanorotor

Torque sensors such as the torsion balance enabled the first determination of the gravitational constant by Cavendish and the discovery of Coulomb's 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…

Stability and dynamics of optically levitated dielectric disks in a Gaussian standing wave beyond the harmonic approximation

Forces and torques exerted on dielectric disks trapped in a Gaussian standing wave are analyzed theoretically for disks of radius $2~μ\text{m}$ with index of refraction $n=1.45$ and $n=2.0$ as well as disks of radius 200 nm with $n=1.45$. Calculations of the forces and torques were conducted both analytically and numerically using a discrete-dipole approximation method. Besides harmonic terms, third order ro-translational coupling terms in the potential energy can be significant and a necessary consideration when describing the dynamics of disks outside of the Rayleigh limit. The coupling term…

真空中光悬浮磷酸钛氧钾纳米晶体的二次谐波产生

Second-harmonic generation from an optically levitated KTP nanocrystal in vacuum

研究在真空中光悬浮磷酸钛氧钾（KTP）纳米晶体并探究其二次谐波产生特性，利用光悬浮系统的高信噪比环境，激光既用于悬浮又作基波，证明光扭矩可控制纳米晶体取向，为真空非线性光学研究开辟新途径。

Precession Motion in Levitated Optomechanics

We investigate experimentally the dynamics of a non-spherical levitated nanoparticle in vacuum. In addition to translation and rotation motion, we observe the light torque-induced precession and nutation of the trapped particle. We provide a theoretical model, which we numerically simulate and from which we derive approximate expressions for the motional frequencies. Both, the simulation and approximate expressions, we find in good agreement with experiments. We measure a torque of $1.9 \pm 0.5 \times 10^{-23}$ Nm at $1 \times 10^{-1}$ mbar, with an estimated torque sensitivity of $3.6 \pm 1.1…

Electrically Driven, Optically Levitated Microscopic Rotors

We report on the electrically driven rotation of $2.4~μ$m-radius, optically levitated dielectric microspheres. Electric fields are used to apply torques to a microsphere's permanent electric dipole moment, while angular displacement is measured by detecting the change in polarization state of light transmitted through the microsphere (MS). This technique enables greater control than previously achieved with purely optical means because the direction and magnitude of the electric torque can be set arbitrarily. We measure the spin-down of a microsphere released from a rotating electric field, th…

Control and measurement of electric dipole moments in levitated optomechanics

Levitated optomechanical systems are rapidly becoming leading tools for precision sensing, enabling a high level of control over the sensor's center of mass motion, rotation and electric charge state. Higher-order multipole moments in the charge distribution, however, remain a major source of backgrounds. By applying controlled precessive torques to the dipole moment of a levitated microsphere in vacuum, we demonstrate cancellation of dipole-induced backgrounds by 2 orders of magnitude. We measure the dipole moments of ng-mass spheres and determine their scaling with sphere size, finding that …

利用光辐射对任意形状悬浮介电物体的最优位移检测

Optimal displacement detection of arbitrarily-shaped levitated dielectric objects using optical radiation

提出基于Fisher信息的方法，实现任意形状悬浮介电物体的最优位移检测，并通过与球形粒子方法对比验证，分析了高纵横比盘状和棒状物体的检测极限。

由悬浮光力学传感器探测的结构化横向轨道角动量

Structured transverse orbital angular momentum probed by a levitated optomechanical sensor

本研究通过两束平行反向传播线偏振聚焦光束的干涉场生成携带本征横向轨道角动量（TOAM）的同旋向涡旋阵列，并利用光学悬浮硅纳米棒光力学传感器直接探测TOAM，为基础物理、光操控及量子光力学研究提供新方法。

Torsional optomechanics of a levitated nonspherical nanoparticle

An optically levitated nanoparticle in vacuum is a paradigm optomechanical system for sensing and studying macroscopic quantum mechanics. While its center-of-mass motion has been investigated intensively, its torsional vibration has only been studied theoretically in limited cases. Here we report the first experimental observation of the torsional vibration of an optically levitated nonspherical nanoparticle in vacuum. We achieve this by utilizing the coupling between the spin angular momentum of photons and the torsional vibration of a nonspherical nanoparticle whose polarizability is a tenso…

6 GHz hyperfast rotation of an optically levitated nanoparticle in vacuum

We report an experimental observation of a record-breaking ultra-high rotation frequency about 6 GHz in an optically levitated nanoparticle system. We optically trap a nanoparticle in the gravity direction with a high numerical aperture (NA) objective lens, which shows significant advantages in compensating the influences of the scattering force and the photophoretic force on the trap, especially at intermediate pressure (about 100 Pa). This allows us to trap a nanoparticle from atmospheric to low pressure ($10^{-3}$ Pa) without using feedback cooling. We measure a highest rotation frequency a…