Demonstrating and exploiting the quantum nature of larger, more macroscopic mechanical objects would help us to directly investigate the limitations of quantum-based measurements and quantum information protocols, as well as test long standing questions about macroscopic quantum coherence. The field of cavity opto- and electro-mechanics, in which a mechanical oscillator is parametrically coupled to an electromagnetic resonance, provides a practical architecture for the manipulation and detection of motion at the quantum level. Reaching this quantum level requires strong coupling, interaction timescales between the two systems that are faster than the time it takes for energy to be dissipated. By incorporating a free-standing, flexible aluminum membrane into a lumped-element superconducting resonant cavity, we have increased the single photon coupling strength between radio-frequency mechanical motion and resonant microwave photons by more than two orders of magnitude beyond the current state-of-the-art. A parametric drive tone at the difference frequency between the two resonant systems dramatically increases the overall coupling strength. This has allowed us to completely enter the strong coupling regime. This is evidenced by a maximum normal mode splitting of nearly six bare cavity line-widths. Spectroscopic measurements of these dressed states are in excellent quantitative agreement with recent theoretical predictions. The basic architecture presented here provides a feasible path to ground-state cooling and subsequent coherent control and measurement of the quantum states of mechanical motion.
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