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Abstract

Faithful conversion of quantum signals between microwave and optical
frequency domains is crucial for building quantum networks based on
superconducting circuits. Optoelectromechanical systems, in which microwave and
optical cavity modes are coupled to a common mechanical oscillator, are a
promising route towards this goal. In these systems, efficient, low-noise
conversion is possible using a mechanically dark mode of the fields but the
conversion bandwidth is limited to a fraction of the cavity linewidth. Here, we
show that an array of optoelectromechanical transducers can overcome this
limitation and reach a bandwidth that is larger than the cavity linewidth. The
coupling rates are varied in space throughout the array so that the
mechanically dark mode of the propagating fields adiabatically changes from
microwave to optical or vice versa. This strategy also leads to significantly
reduced thermal noise with the collective optomechanical cooperativity being
the relevant figure of merit. Finally, we demonstrate that, quite surprisingly,
the bandwidth enhancement per transducer element is largest for small arrays;
this feature makes our scheme particularly attractive for state-of-the-art
experimental setups.