Complex stochastic dynamics of heavy particles optically levitated in vacuum in the photon noise regime
Host laboratory : Laboratoire Ondes et Matière d’Aquitaine (LOMA), University of Bordeaux
Keywords: Vacuum Levito-dynamics, Optical Trapping, Mie Theory, Langevin Equation
Context of the Project
The dynamics of optically trapped scatterers in vacuum has emerged as a major topic, since roughly a decade. These latter are trapped in a light beam, and behave as Brownian (noisy) underdamped oscillator. Both fundamental questions (the route to the quantum ground state for macroscopic objects) and Applied Physics (force and torque sensors) are at stake.
In the recent years, our group has understood the influence of very weak non-conservative forces [1], and studied the torque transfer from the laser beam to matter [2, 3]. Nowadays, the Brownian dynamics of a ‘small’ levitating nano-object is well known, in the regime where thermal noise dominates.
Today, a main stake is to use heavier particles, so as to enhance the sensitivity of accelerometers and gyroscopes, especially in the low pressure limit, where laser intensity fluctuations dominate.
Objectives and planned work
This theoretical / numerical Ph-D will focus on the regime where the Brownian motion is driven by its (Poissonian) intensity fluctuations. Our goal is to trap more massive particles.
Both the trapping potential and the photon recoil damping will be controled through the multipolar scattering of the particle. To do this, we shall use spatially modulated wavefronts (implemented, e.g. with SLM technology), to encode specific phase lags between different multipolar contributions of optical forces.
Our preliminary results shows that modal engineering permits to optimize the beam in order to trap micrometric spherical particles (r > λ). It is a breakthrough in vacuum levitodynamics, where, a regular tweezer beam can barely trap 150 nm particles. See Fig. 1, for an example.
The Ph-D shall propose single beam trapping designs for large particles, with a minimal Joule heating inside the material. Numerical Langevin simulation coupled to theoretical scattering models will be used, to understand the effect of photon noise on the dynamics of large particles. Tuning the scattering modes (e.g. their relative phase) will permit a new degree of control on the trapping potential as well as on the force noise, that were totally absent in the thermal regime – where fluctuations are only due to collisions with buffer gas.
[1] Amarouchene et. al, Phys. Rev. Lett. 122, 183901 (2019)
[2] Reiman et al., Phys Rev. Lett. 121, 033602 (2018).
[3] Bellando et al. Phys. Rev. Lett 129, 023602 (2022).
Candidate Profile
We look for a candidate with a master’s degree in Physics, with strong interest and capabilities in nano-optics, willing to make numerical simulation. Knowledge of programming langages (e.g. Matlab) and numerical tools is a must. The candidate will work in close connection with an experimental group. Therefore, we seek a person with capabilities to work in a team, and who has good oral and written communications skills in English.
Working environement
The Ph-D will be hosted at LOMA, and benefit from the expertise of the Photonics team, and the help of several permanent researchers. He/she will have the opportunity to use several tools already developed in situ (numerical codes). The candidate will learn to work independently in a multidisciplinary environment, in collaboration with Physiscists (numerics + experimentalists).
Funding
Ph-D Starting date : before December 2025 Contract duration : 36 months
Closing of the recruitement procedure : end of May 2025
To apply
Interested candidates are invited to send a CV, a motivation letter, their marks record and rating in the Master years, and letter(s) of recommandation to mathias.perrin ‘at’ u-bordeaux.fr