Magnons in a sphere squeezed to quantum limit ⚡ экспресс
Squeezed states play a key role in quantum metrology and technologies, but quantum squeezing of magnons in macroscopic spin systems had not been observed before. This work presents the experimental observation of quantum squeezing of magnons in a millimeter-sized yttrium iron garnet (YIG) sphere. By using strong dispersive coupling between magnons and a superconducting qubit via a microwave resonator, a significant Kerr nonlinearity was created, enabling the generation of squeezed magnon states with an average magnon number below one. A magnon-assisted Raman process was used for Wigner tomography, which revealed a quadrature variance of about 0.8 (~1 dB squeezing) relative to vacuum. These results lay the foundation for quantum nonlinear magnonics and open up prospects for quantum metrology.
There is always noise in the microworld. Even in absolute emptiness, something trembles, and these quantum fluctuations interfere with precise measurements. But noise can be "squeezed," like a balloon: if you squeeze it from the sides, one part gets thinner while the other bulges. This way, the overall uncertainty, discovered by Heisenberg, doesn't vanish but gets redistributed. That's exactly the squeezing used in detectors like LIGO, for which Rainer Weiss won the Nobel Prize.
Now physicists have squeezed not light, but magnons—collective waves in a magnetic material. A tiny sphere of yttrium iron garnet—the same material found in cell towers to clean signals—was placed in a resonant cavity and coupled with a quantum qubit. This allowed such precise control of the oscillations that on average, there wasn't even one full wave inside the sphere. A special technique (Raman scattering) showed that one side of the noise became quieter by 1 decibel—the first squeezing of magnons in a visible object.
This isn't just a lab trick. Squeezed magnons could become the basis of quantum electronics based on magnetic waves—magnonics. They already promise ultra-sensitive sensors for detecting magnetic fields, and in the future, networks of quantum processors transmitting information not with current, but with waves of magnetization.
🎯 A magnon isn't a particle but a quantum of a collective wave: trillions of spins move together, like spectators in a stadium doing the wave in sync.