Unconventional magnon excitation by off-resonant microwaves

It is widely recognized that a magnetic system can only respond to a periodic driving significantly when the driving frequency matches the normal mode frequency of the magnet, which leads to magnetic resonance. Off-resonant phenomena are rarely considered for the diffculty to realize strong coupling between magnons and off-resonant waves. Here we examine the response of a magnetic system to squeezed light and surprisingly find that the magnons are maximally excited when the effective driving frequency is several orders of magnitude larger than the resonant frequency. The generated magnons are squeezed which brings the advantage of tunable squeezing through an external magnetic field. Further, we demonstrate that such off-resonant quasi-particle excitation is purely a quantum effect, which is rooted in the quantum fluctuations of particles in the squeezed vacuum. Our findings may provide an unconventional route to study off-resonant phenomena in a magnetic system and may further benefit the use of hybrid magnet-light systems in continuous variable quantum information.