Nano-strings swing circuit QED*

In nano-electromechanics, quantum mechanical phenomena can be studied in the literal sense. For example, the coupling of a nanomechanical element to a superconducting resonator allows to cool the mechanical mode to its ground state and to squeeze its motion. Replacing the linear microwave resonator with a nonlinear one enables the preparation of more complex non-classical mechanical states.
In this presentation, we discuss various opto-mechanical coupling schemes in nano-electromechanical circuits employing nonlinear elements. In this context, Josephson junctions in superconducting circuit environments are the obvious choice. In particular, we envisage the scenario of a mechanically compliant tensile string embedded in a resonator including Josephson junctions, e.g. a transmon qubit or a flux-tunable resonator. We discuss realistically achievable opto-mechanical coupling strengths for these circuit layouts. In addition, we set this in context with the limitations imposed by such circuits, in particular in view of the photon numbers. Such hybrid systems open new perspectives in the field of optomechanics ranging from sensing applications to the preparation of quantum states.