Nonreciprocal entanglement of ferrimagnetic magnons and nitrogen-vacancy-center ensembles by Kerr nonlinearity

We propose a scheme to generate nonreciprocal entanglement between an yttrium iron garnet (YIG) sphere and two nitrogen-vacancy-center ensembles by magnon Kerr effects in a transmission-line resonator. By driving the YIG sphere appropriately, strong Kerr nonlinearities emerge and then induce magnon parametric amplification and magnon frequency shift, resulting in the appearance of optimal entanglements. Depending on the direction of the bias magnetic field, macroscopic nonreciprocal entanglement is realized in this all-solid-state quantum system, which may find potential applications in chiral quantum information processing.