  Quantum illumination (QI) is a quantum sensing protocol mainly for target
detection which uses entangled signal-idler photon pairs to enhance the
detection efficiency of low-reflectivity objects immersed in thermal noisy
environments. Especially, due to the naturally occurring background radiation,
the photon emitted toward potential targets more appropriately lies in the
microwave region. Here, we propose a hybrid quantum source based on cavity
magnonics for microwave QI, where the medium that bridges the optical and the
microwave modes is magnon, the quanta of spin wave. Within experimentally
accessible parameters, significant microwave-optical quantum resources of
interest can be generated, leading to orders of magnitude lower detecting error
probability compared with the electro-optomechanical prototype quantum radar
and any classical microwave radar with equal transmitted energy.
