Enhancement Of Magnon Entanglement Based On Quantum Feedback

Recently,how to obtain high entanglement between magnons in YIG magnets is one of the forefront research topics in the subject of quantum optics.Magnons entanglement in micromagnets can not only be used to verify macroscopic quantum effects,but also has important applications in macroscopic quantum devices and quantum information processing.Due to the high spin density of yttrium iron garnet(YIG)material,the strong coupling between photons and magnons can be achieved,and magnons have a very low dissipation rate,which lays the foundation for the entanglement between magnons.This paper investigates the entanglement between the magnons in two short-distance YIG microspheres placed in the same microwave cavity and the entanglement between the magnons in two long-distance YIG microspheres placed in two unidirectionally coupled microwave cavities.And consider the use of measurement-based quantum feedback to improve the entanglement between magnons.Firstly,this paper briefly introduces the basic knowledge of cavity-magnon system,the definition and criterion of entanglement.Secondly,consider placing two YIG microspheres with Kerr nonlinearity in a microwave cavity driven by a continuous laser to study the stable entanglement properties between magnons.The analysis found that in the linear stable region of the system,there is entanglement between the two magnons in the cavity,but the entanglement is weak.In order to improve the entanglement between the magnons,it is considered to introduce measurement-based quantum feedback into the system,that is,to detect the cavity field output through continuous homodyne measurement,and then feedback the measurement results to the magnon system.Through analysis,it is found that quantum feedback can effectively improve the entanglement between magnons,and the improvement of entanglement is closely related to the continuous measurement angle and feedback drive phase.We discussed in detail the influence of the two changes on entanglement and determined the best measurement Angle and drive phase.Finally,based on the above research,consider placing two YIG microspheres with Kerr nonlinearity in two long-distance unidirectionally coupled microwave cavities,continuously driving the first cavity,and using its output field to drive the second cavity.Studying the stable entanglement properties between the magnons in the two cavities at this time.Through analysis,we find that the entanglement between two long-distance magnons is weaker than the entanglement between two magnons placed in the same cavity in the linear stable region of the system.Similarly,in order to improve the entanglement between magnons,consider introduce measurement-based quantum feedback into the system,consider detecting the output of the second cavity field through continuous homodyne measurement,and then feedback the measurement results to the two cavity fields,Through analysis,it is found that feedback can also effectively improve the entanglement between magnons,and the maximum stable entanglement of two cavities after feedback is added is less than the maximum stable entanglement of one cavity.In addition,we also discussed in detail the relationship between entanglement changes with the measurement angle and drive phase,and found the best measurement angle and drive phase,discussed the relationship between entanglement and feedback intensity,and determined the best intensity.