Ultra-strong coupling of electron tunneling and mechanical motion in carbon nanotube electromechanical resonators

A single quantum dot electrostatically defined in a carbon nanotube-based mechanical resonator is a promising testbed for exploring electron-phonon coupling. The tunnelling of electrons generates back action on the nanomechanical resonator, an effect known as softening of the mechanical frequency. The dynamics of these electromechanical resonators are determined by two main energy scales: the tunnel coupling of the quantum dot with the leads and the resonance frequency of the mechanical oscillator. We study the magnitude of electromechanical coupling in various regimes. We find an ultra-strong coupling regime for fast electron tunnelling under the adiabatic approximation. I will discuss how these findings establish carbon nanotube-based electromechanical devices as a fertile platform for exploring non-equilibrium thermodynamics.