Quantifying quantum correlations in a double cavity–magnon system

In this paper, we study a system consisting of two spatially separated cavities, where each cavity contains a magnon mode of YIG sphere coupled to a microwave cavity mode via a linear beam splitter interaction. The two cavities are driven by two-mode squeezed vacuum field. In (Yu et al. in J. Phys. B: At. Mol. Opt. Phys. 53:065402, 2020), it has been investigated about the logarithmic negativity as a measure of quantum entanglement between two magnon modes versus various system parameters. Motivated by this, we will look at two different types of quantum correlations (i.e., entanglement and discord) in two-mode Gaussian subsystems (cavity–cavity modes and magnon–magnon modes). We analyze the robustness of these correlations with respect to the physical and environmental parameters—temperature, squeezing and the cavity–magnon coupling—of the two studied subsystems. For this, we use the Gaussian Bures distance to quantify entanglement and the Gaussian geometric discord (GGD) to quantify correlations beyond entanglement. The entanglement of the two bi-mode subsystems proves to be more sensitive to thermal noise. In particular, under the effect of temperature, the magnon–magnon entanglement degrades much more than the cavity–cavity entanglement. In addition, the GGD is found to be more robust—in both subsystems—against thermal noise, and it can be detected even for high values of temperatures. Also, we show that nonzero quantum correlations can be captured even when entanglement vanishes completely in the two studied subsystems. Finally, two different types of entanglement transfer (i.e., light → light and light → matter) have been observed in the studied system. Graphical abstract