Nonlinear Nanomechanical Resonator Approaching the Quantum Ground State*

We present measurements of a strong mechanical nonlinearity near the quantum ground state. The mechanical nonlinearity is generated by the ultrastrong coupling (500MHz) of a carbon nanotube mechanical resonator (30MHz) to an embedded quantum dot undergoing single-electron tunneling. The nonlinearity is far bigger than what has been realized thus far and results in highly nonlinear thermal vibrations. As the average displacement amplitude is decreased to 13 times the zero-point motion, approximately 42% of the thermal energy is stored in the anharmonic part of the potential. We also present transport measurements of clean and regular double quantum dot devices defined using a novel nanofabrication process. Such devices are necessary to coherently manipulate the nonlinear mechanical resonator in order to create mechanical qubit [1]. 

[1] F. Pistolesi, et al., PRX 11, 031027 (2021)