Title: Strongly nonlinear nanomechanical resonators approaching the quantum ground state

Speaker: Dr. Chandan Samanta, Institute of Photonic Sciences (ICFO), Spain

Abstract: The realization of nonlinearity in mechanical vibrations in the quantum regime has been considered unfeasible for the past two decades, as previous studies have shown that nonlinearity only emerges for vibration amplitudes that are orders of magnitude larger than the zero-point motion. This requires engineering a mechanical nonlinearity far beyond what has been realized thus far. As a result, all efforts have been solely focused on the quantum manipulation of mechanical vibrations using linear resonators. In my talk, I will present an overview of the mechanical resonator and the most recent developments in this field. Then, I will explain how we resolve the aforementioned open question by showing a nonlinear mechanical resonator operated near its quantum ground state. We discovered a mechanism to boost the Duffing nonlinearity by coupling a mechanical resonator to an embedded two-level system and by operating the system in the ultrastrong coupling regime. This new mechanism displays remarkable physics, contrary to what was expected, as the nonlinearity becomes larger as the vibrations are cooled closer to the ground state. The average vibration amplitude at the lowest temperature is 13 times the zero-point motion, with approximately 42% of the thermal energy stored in the anharmonic part of the potential. Our work will have an important impact on future developments in the field of mechanical systems. It opens a whole new realm of possibilities in quantum science and technology, including the development of mechanical qubits and mechanical ‘Schrödinger cat’ states.