Speaker: Carlos González-Ballestero
Affiliation: Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
Date: Friday, 15 March 2019 at 11:30
Location: Seminar Room, Serrano 113b
The possibility of levitating very small particles in controlled environments has brought forth
a whole new field of research: levitodynamics. In the last few years, significant experimental advances have been reported, e.g. the achievement of stable levitation in ultra-high vacuum, and the levitation of particles of many different shapes and materials. One of the most sought goals of current levitodynamics experiments is the cooling of the center of mass (COM) motion to the mechanical
ground state, as such a milestone would allow to access the quantum regime of an extremely isolated nanomechanical oscillator. Moreover, the extreme isolation and confinement of levitated particles suggests that the behavior of internal degrees of freedom in these systems (electrons, phonons, magnons…) might significantly differ from bulk matter or from less isolated nanoparticles.
In my talk, I will present our results on both the external (COM) dynamics and the internal
dynamics of levitated nanoparticles (NPs). In the first part, I will introduce our recent theoretical
model describing the cavity-assisted cooling of the COM temperature of a levitated NP via coherent
scattering into an optical cavity [1]. This full quantum model extends on previous results by including
all relevant degrees of freedom and a detailed analysis of the decoherence mechanisms, and is
benchmarked by quantitatively reproducing the recent experiments reporting, for the first time, three-
dimensional cooling near the ground state [2]. I will further demonstrate how ground state cooling is
attainable with state of the art experiments, indicating that such a milestone is likely to be reached in
the near future.
In the second part of the talk, I will move on from external to internal dynamics, specifically
to the phenomenon of radiative thermalization in levitated NPs. I will argue why the extreme
confinement and isolation of the NP should make the usual quasi-equilibrium theoretical models fail
in high vacuum levitodynamics setups. Based on these arguments, I will introduce a theoretical toy
model of a NP which, on the one hand, allows to recover all its measurable thermal and optical
properties and, on the other hand, is exactly solvable [3]. Such exact solution evidences that, according
to our model, radiative thermalization in these systems is a largely out-of-equilibrium process, where
previous models do indeed fail and where temperature cannot be defined. This is only one among
many examples showing the new regimes of condensed matter and light-matter interaction arising in
levitodynamics experiments.
[1] C. Gonzalez-Ballestero, P. Maurer, D. Windey, L. Novotny, R. Reimann, O. Romero-Isart, arXiv: 1902.01282 (2019)
[2] Dominik Windey, C. Gonzalez-Ballestero, P. Maurer, L. Novotny, O. Romero-Isart, R. Reimann, arXiv: 1812.09176 (2018)
[3] A. E. Rubio López, C. Gonzalez-Ballestero, and O. Romero-Isart, Phys. Rev.B 98, 155405 (2018)