Optomechanical cavity cooling of levitated objects offers the possibility for laboratory investigation of the macroscopic quantum behavior of systems that are largely decoupled from their environment. However, experimental progress has been hindered by particle loss mechanisms, which have prevented levitation and cavity cooling in a vacuum. We overcome this problem with a new type of hybrid electro-optical trap formed from a Paul trap within a single-mode optical cavity. We demonstrate a factor of 100 cavity cooling of 400 nm diameter silica spheres trapped in vacuum. This paves the way for ground-state cooling in a smaller, higher finesse cavity, as we show that a novel feature of the hybrid trap is that the optomechanical cooling becomes actively driven by the Paul trap, even for singly charged nanospheres.

Einstein realized that the fluctuations of a Brownian particle can be used to ascertain the properties of its environment. A large number of experiments have since exploited the Brownian motion of colloidal particles for studies of dissipative processes, providing insight into soft matter physics and leading to applications from energy harvesting to medical imaging. Here, we use heated optically levitated nanospheres to investigate the non-equilibrium properties of the gas surrounding them. Analysing the sphere's Brownian motion allows us to determine the temperature of the centre-of-mass motion of the sphere, its surface temperature and the heated gas temperature in two spatial dimensions. We observe asymmetric heating of the sphere and gas, with temperatures reaching the melting point of the material. This method offers opportunities for accurate temperature measurements with spatial resolution on the nanoscale, and provides a means for testing non-equilibrium thermodynamics.

Classical thermodynamics is unrivalled in its range of applications and relevance to everyday life. It enables a description of complex systems, made up of microscopic particles, in terms of a small number of macroscopic quantities, such as work and entropy. As systems get ever smaller, fluctuations of these quantities become increasingly relevant, prompting the development of stochastic thermodynamics. Recently we have seen a surge of interest in exploring the quantum regime, where the origin of fluctuations is quantum rather than thermal. Many questions, such as the role of entanglement and the emergence of thermalisation, lie wide open. Answering these questions may lead to the development of quantum heat engines and refrigerators, as well as to vitally needed simple descriptions of quantum many-body systems.

Optically levitated nano-objects in vacuum are amongst the highest-quality mechanical oscillators, and thus of great interest for force sensing, cavity quantum optomechanics, and nanothermodynamic studies. These precision applications require exquisite control. Here, we present full control over the rotational and translational dynamics of an optically levitated silicon nanorod. We trap its centre-ofmass and align it along the linear polarization of the laser field. The rod can be set into rotation at a predefined frequency by exploiting the radiation pressure exerted by elliptically polarized light. The rotational motion of the rod dynamically modifies the optical potential, which allows tuning of the rotational frequency over hundreds of Kilohertz. Through nanofabrication, we can tailor all of the trapping frequencies and the optical torque, achieving reproducible dynamics which are stable over months, and analytically predict the motion with great accuracy. This first demonstration of full ro-translational control of nanoparticles in vacuum opens up the fields of rotational optomechanics, rotational ground state cooling and the study of rotational thermodynamics in the underdamped regime.

Optomechanics is concerned with the use of light to control mechanical objects. As a field, it has been hugely successful in the production of precise and novel sensors, the development of low-dissipation nanomechanical devices, and the manipulation of quantum signals. Micro-and nano-particles levitated in optical fields act as nanoscale oscillators, making them excellent lowdissipation optomechanical objects, with minimal thermal contact to the environment when operating in vacuum. Levitated optomechanics is seen as the most promising route for studying high-mass quantum physics, with the promise of creating macroscopically separated superposition states at masses of 10 6 amu and above. Optical feedback, both using active monitoring or the passive interaction with an optical cavity, can be used to cool the centre-of-mass of levitated nanoparticles well below 1 mK, paving the way to operation in the quantum regime. In addition, trapped mesoscopic particles are the paradigmatic system for studying nanoscale stochastic processes, and have already demonstrated their utility in state-of-the-art force sensing. * Electronic address: james.millen@kcl.ac.uk arXiv:1907.08198v1 [physics.optics] 18 Jul 2019It is a pleasant coincidence, that whilst writing this review the Nobel Prize in Physics 2018 was jointly awarded to the American scientist Arthur Ashkin, for his development of optical tweezers. By focusing a beam of light, small objects can be manipulated through radiation pressure and/or gradient forces. This technology is now available offthe-shelf due to its applicability in the bio-and medical-sciences, where it has found utility in studying cells and other microscopic entities.The pleasant coincidences continue, when one notes that the 2017 Nobel Prize in Physics was awarded to Weiss, Thorne and Barish for their work on the LIGO gravitational wave detector. This amazingly precise experiment is, ultimately, an optomechanical device, where the position of a mechanical oscillator is monitored via its coupling to an optical cavity. The field of optomechanics is in the ascendency [1], showing great promise in the development of quantum technologies and force sensing. These applications are somewhat limited by unavoidable energy dissipation and thermal loading at the nanoscale [2], which despite impressive progress in soft-clamping technology [3] means that these technologies will likely always operate in cryogenic environments.Enter the work of Ashkin: he showed that dielectric particles could be levitated and cooled under vacuum conditions in 1977 [4]. By levitating particles at low pressures, they naturally decouple from the thermal environment, and since the mechanical mode is the centre-of-mass motion of a particle, energy dissipation via strain vanishes. The field of levitated optomechanics really took off in 2010, when three independent proposals illustrated that levitated nanoparticles could be coupled to optical cavities [5][6][7]. This promises cooling to the quantum regime, and state engineering once you are t...

Optomechanical systems explore and exploit the coupling between light and the mechanical motion of matter. A nonlinear coupling offers access to rich new physics, in both the quantum and classical regimes. We investigate a dynamic, as opposed to the usually studied static, nonlinear optomechanical system, comprising of a nanosphere levitated and cooled in a hybrid electro-optical trap. An optical cavity offers readout of both linear-in-position and quadratic-in-position (nonlinear) light-matter coupling, whilst simultaneously cooling the nanosphere to millikelvin temperatures for indefinite periods of time in high vacuum. We observe cooling of the linear and non-linear motion, leading to a 10 5 fold reduction in phonon number np, attaining final occupancies of np = 100 − 1000. This work puts cavity cooling of a levitated object to the quantum ground-state firmly within reach.Cavity optomechanics, the cooling and coherent manipulation of mechanical oscillators using optical cavities, has undergone rapid progress in recent years [1], with many experimental milestones realized. These include cooling to the quantum level [2,3], optomechanically induced transparency (OMIT) [4], and the transduction [5][6][7] and squeezing [8] of light. These important processes are due to a linear light-matter interaction; linear in both the position of the oscillatorx and the amplitude of the optical fieldâ.Nonlinear optomechanical interactions open up a new range of applications which are so far largely unexplored. In principle, they allow quantum nondemolition (QND) measurements of energy and thus the possibility of monitoring quantum jumps in a macroscopic system [1,9]. They also offer the prospect of observing phonon quantum shot noise [10], nonlinear OMIT [11,12], and the preparation of macroscopic nonclassical states [13]. To achieve a nonlinear interaction one can use optical means, which require strong single-photon coupling to the mechanical system [11,12] but are a considerable experimental challenge. Nonlinearities can also arise from spatial, mechanical effects, by engineering, for example, a light-matter interaction of the form (â+â † )(G 1x +G 2x 2 ). Previous studies investigated the static shift in the cavity resonant frequency [9,14,15] or the quadratic optical spring effect [15] arising from a nonlinear coupling. However, these studies identified the problem of a residual linear G 1 contribution to the coupling. Not only can G 1 allow unwanted back-action, but a large G 2 1 contribution (e.g. [14]) can mask the signatures of true nonlinear G 2 coupling.In this work, we study a nanosphere levitated in a hybrid system formed from a Paul trap and an optical cavity [16] as shown in fig 1. The output of the cavity is used to access the linear and nonlinear dynamics of the particle. We are able to tune the G 1 : G 2 ratio to reach G 2 G 1 , isolating the true nonlinear dynamics. Further, due to the dynamic nature of this experiment, we are able to observe the cooling, in time, of the nonlinear contribution to motion. To ...

Nanomechanical devices have attracted the interest of a growing interdisciplinary research community, since they can be used as highly sensitive transducers for various physical quantities. Exquisite control over these systems facilitates experiments on the foundations of physics. Here, we demonstrate that an optically trapped silicon nanorod, set into rotation at MHz frequencies, can be locked to an external clock, transducing the properties of the time standard to the rod’s motion with a remarkable frequency stability f r/Δf r of 7.7 × 1011. While the dynamics of this periodically driven rotor generally can be chaotic, we derive and verify that stable limit cycles exist over a surprisingly wide parameter range. This robustness should enable, in principle, measurements of external torques with sensitivities better than 0.25 zNm, even at room temperature. We show that in a dilute gas, real-time phase measurements on the locked nanorod transduce pressure values with a sensitivity of 0.3%.

Abstract. We explore the prospects for confining alkaline-earth Rydberg atoms in an optical lattice via optical dressing of the secondary core valence electron. Focussing on the particular case of strontium, we identify experimentally accessible magic wavelengths for simultaneous trapping of ground and Rydberg states. A detailed analysis of relevant loss mechanisms shows that the overall lifetime of such a system is limited only by the spontaneous decay of the Rydberg state, and is not significantly affected by photoionization or autoionization. The van der Waals C 6 coefficients for the Sr(5sns 1 S 0 ) Rydberg series are calculated, and we find that the interactions are attractive. Finally we show that the combination of magic-wavelength lattices and attractive interactions could be exploited to generate many-body Greenberger-HorneZeilinger (GHZ) states.