Intrinsic Phononic Dressed States in a Nanomechanical System
Nanoelectromechanical systems (NEMS) provide a platform for probing the quantum nature of mechanical motion in mesoscopic systems. This nature manifests most profoundly when the device vibrations are nonlinear and, currently, achieving vibrational nonlinearity at the single-phonon level is an active area of pursuit in quantum information science. Despite much effort, however, this has remained elusive. Here, we report the first observation of intrinsic mesoscopic vibrational dressed states. The requisite nonlinearity results from strong resonant coupling between an eigenmode of our NEMS resonator and a single, two-level system (TLS) that is intrinsic to the device material. We control the TLS in situ by varying mechanical strain, tuning it in and out of resonance with the NEMS mode. Varying the resonant drive and/or temperature allows controlled ascent of the nonequidistant energy ladder and reveals the energy multiplets of the hybridized system. Fluctuations of the TLS on and off resonance with the mode induces switching between dressed and bare states; this elucidates the complex quantum nature of TLS-like defects in mesoscopic systems. These quintessential quantum effects emerge directly from the intrinsic material properties of mechanical systems - without need for complex, external quantum circuits. Our work provides long-sought insight into mesoscopic dynamics and offers a new direction to harness nanomechanics for quantum measurements.