Séminaire

Vendredi 4 Octobre 2024 à 11h00.

Two applications of feedback control on a nano and micro-system: Thermodynamic of Information & Optical Levitation in the Dark

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When dealing with nano and micro-systems, whose dynamics are ruled by thermal fluctuations, feedback schemes represent a great tool for controlling them. In this talk we will discuss two experiments in which underdamped Brownian objects are used in combination with optimised feedback control to probe fundamental physics -thermodynamic of information-in the one hand, and improve levitation techniques in the other.
First, we demonstrate how a feedback loop can create a virtual double-potential for an underdamped micro-mechanical oscillator, in order to be used as a 1-bit memory. The feedback control allows to precisely tune the potential and to follow elaborate procedures. Hence the 1-bit information encoded by the system’s position in the virtual double-well can be manipulated to operate reset and bitflip operations. This platform is used to implement fast 1-bit logical operations and study the energetic cost of information treatment in the underdamped regime [1,2,3].
In a second part, we tackle the use of feedback for quantum control of nanospheres. Feedback cooling of levitated nanospheres in an optical trap is a well-established technique, that combined with a quantum limited detection of the particle motion enables reaching the motional ground state [4]. However, standard optical levitation method still faces a significant challenge: the intense optical fields used result in light absorption and subsequent internal heating of the trapped object, causing material limitations (melting issue) and high blackbody decoherence. We propose an original approach to overcome the above-mentioned optical levitation limitation: it consists in maintaining the particle in the dark spot (intensity minimum) of a higher laser mode (e.g., the tip of a double-well potential) while still allowing optimal optical displacement detection. Contrary to the harmonic potential of standard optical traps, this equilibrium point is unstable, and thus, active feedback is obligatory to keep the particle in the dark. We demonstrate levitation in the dark configuration in the experimental double-well setup without the need for any confining potential in 1D, where feedback control provides the cooling and the stabilization the particle’s position.

[1] S. Dago, J. Pereda, S. Ciliberto, and L. Bellon. Virtual double-well potential for an underdamped oscillator created by a feedback loop. Journal of Statistical Theory and Experiment, 2022(5):053209, May 2022.
[2] S. Dago, J. Pereda, N. Barros, S. Ciliberto, and L. Bellon. Information and thermodynamics: Fast and precise approach to landauer’s bound in an underdamped micromechanical oscillator. Phys.Rev. Lett., 126:170601, 2021.
[3] S. Dago, L. Bellon. Logical and thermodynamical reversibility: optimized experimental implementation of the not operation. Phys. Rev. E 108, L022101 ,August 2023
[4] L. Magrini, P. Rosenzweig, C. Bach, A. Deutschmann-Olek, S. G. Hofer, S. Hong, N. Kiesel, A. Kugi, and M. Aspelmeyer. Real-time optimal quantum control of mechanical motion at room temperature. Nature 595, 373 (2021).

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