Enhancement of Magnon-Magnon Entanglement in a Double Cavity-Magnon System by Optical Parametric Amplifier

The paper investigates the behavior of the magnon-magnon entanglement in a double cavity-magnon system with optical parametric amplifiers (OPA) and where both cavities are coupled by the photon tunneling process. Using the standard Langevin approach, the explicit expression is suggested for the covariance matrix describing the two magnon modes and further proved by logarithmic negativity, that the steady state of the indirectly coupled magnons is genuinely entangled. Moreover, the best parameters are obtained to achieve the magnon-magnon entanglement. It is shown that the entanglement robustness against the negative effect of the thermal bath can be enhanced by a proper choice of both the cavity-cavity coupling and the OPA gain.