  Quantum noise and thermal noise are the two primary sources of noise that
limit the sensitivity of weak magnetic field sensing. Although quantum noise
has been widely addressed, effectively reducing thermal noise remains
challenging in detecting weak magnetic fields. We employ an anisotropic
elliptical YIG sphere as a magnetic field probe to establish a parametric
amplification interaction of magnons and induce magnon squeezing effects. These
effects can effectively suppress thermal noise in the magnon mode and amplify
weak magnetic field signals from external sources. Specifically, complete
suppression of thermal noise can be achieved by placing the YIG sphere in a
squeezed vacuum reservoir. Our scheme has the potential to inspire advancements
in thermal noise suppression for quantum sensing.
