Motional Sideband Asymmetry of a Nanoparticle Optically Levitated in Free Space

Abstract

The hallmark of quantum physics is Planck's constant h, whose finite value entails the quantization that gave the theory its name. The finite value of h gives rise to inevitable zero-point fluctuations even at vanishing temperature. The zero-point fluctuation of mechanical motion becomes smaller with growing mass of an object, making it challenging to observe at macroscopic scales. Here, we transition a dielectric particle with a diameter of 136 nm from the classical realm to the regime where its zero-point motion emerges as a sizeable contribution to its energy. To this end, we optically trap the particle at ambient temperature in ultrahigh vacuum and apply active feedback cooling to its center-of-mass motion. We measure an asymmetry between the Stokes and anti-Stokes sidebands of photons scattered by the levitated particle, which is a signature of the particle's quantum ground state of motion.

Quantum motional state tomography with nonquadratic potentials and neural networks

“…We emphasize, however, that the method is very general since a neural network allows to optimally adapt the quantum state tomography to any given physical scenario in an experiment by using training examples from the particular situation. For the case of levitated nanoparticles, ground-state cooling is closely approached [28][29][30][31][46][47][48][49][50][51][52][53] and hence the development of quantum tomography schemes is not only important but timely. At the same time, implementing nonquadratic potentials is also a fantastic tool to prepare non-Gaussian states.…”

“…Let us now introduce the overall procedure: We propose to train the neural network on simulated data and then use the trained network to deduce the initial quantum state from experimentally measured trajectories u 1 (t ) and u 2 (t ). Experimentally, these trajectories could be obtained by repeatedly repreparing a particle in the same initial state and then evolving it (in the absence of measurements) up to a time t 1 when the position is measured, for instance, via optical position detection [28,29]. Averaging over the many repetitions, this reveals the expectation value and variance of the position at this time t 1 .…”

Quantum sensing with nanoparticles for gravimetry: when bigger is better

“…Green dashed line shows recent data of a nanoparticle feedback cooled in an optical tweezer using no cavity for cooling or readout purposes. EPFL '20: [7]; Vienna 2020: [1]; ETH 2020: [8]; ETH 2019: [9]; Delft 2019: [10]; Florence 2019: [11]; Copenhagen 2018: [12]; Boulder 2017: [13]; JILA 2016: [14]; Boulder '11: [15]; Caltech '11: [16]; EPFL '11: [17]; MIT '11: [18]; Cornell '10: [5]; MPQ '09: [19]; Vienna 2009: [20]; JILA 2008: [21].…”

“…This allows energy transfer between the optical and mechanical modes in an anti-Stokes/Stokes process, enabling cooling of the mechanical oscillator. A cavity is not necessarily required to reach the ground state [8], but a cavity provides resonant enhancement in readout and interaction strength. This reduces the number of photons needed to interact with the mechanical oscillator, improving the signal to noise.…”

Search for Composite Dark Matter with Optically Levitated Sensors

“…Techniques to trap micron or submicron sized masses via optical [15][16][17], magnetic [18][19][20][21], or radio frequency [22][23][24][25] fields have progressed substantially in the last decade [26]. Past work has demonstrated the ability to cool particles with ∼ femtogram masses to μK effective temperatures [27][28][29]. Recent extensions of such cooling to masses as large as 1 ng [30] is key to enabling the DM searches presented here.…”