Twice-enhanced quantum entanglement in a dual-coupled auxiliary-sphere-assisted cavity magnomechanical system

We propose a mechanism to significantly enhance the photon-phonon entanglement twice by coupling an auxiliary magnetic sphere to a standard cavity magnomechanical system. The deformed sphere acts as a cold reservoir that can simultaneously cool two hybrid modes superposed over the optical cavity and the mechanical oscillator by modulating the relationship between the coupling strengths, which enables us to obtain large steady-state cavity-oscillator entanglement. On the basis of the double-mode cooling effect, the steady-state photon-phonon entanglement can be significantly improved by opening the single-coupled auxiliary-sphere-assisted channel due to the fact that the nonsuperposed optical mode can be efficiently cooled via the auxiliary sphere. More importantly, the photon-phonon entanglement can be significantly enhanced again by switching the dual-coupled auxiliary-sphere-assisted (DC-ASA) passage, where the auxiliary sphere serves as an additional cold bath to simultaneously cool both the nonsuperposed optical mode and the reservoir mode. Moreover, in the DC-ASA regime, the steady-state entanglement is more robust against the mechanical thermal noise. This DC-ASA scheme can be potentially applied to accelerate magnomechanical cooling and enhance magnomechanical squeezing.