Nanoscale electromechanical coupling provides a unique route towards control of mechanical motions and microwave fields in superconducting cavity electromechanical devices. Though their successes in utilizing the optomechanical or electromechanical back-action effects for various purposes, aluminum imposes severe constraints on their operating conditions with its low superconducting critical temperature (1.2 K) and magnetic field (0.01 T). To extend the potential of the devices, here we fabricate a superconducting electromechanical device employing niobium and demonstrate a set of cavity electromechanical dynamics including back-action cooling and amplification, and electromechanically induced reflection at 4.2 K and in strong magnetic fields up to 0.8 T. This device could be used to realize electromechanical microwave components for quantum technologies by integrating amplifiers, converters, and circulators on a single chip that can be installed at the 4K stage of dilution refrigerators. Moreover, with its ability to control and readout nanomechanical motions simultaneously, this niobium electromechanical transducer could provide powerful nanomechanical sensing platforms.
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