Study On Ground State Cooling Of Magnomechanical Resonator In Parity Time Symmetric Cavity Magnomechanical System

In recent years,the collective excitation of spins in the cavity magnomechanical system has received extensive research attention due to its unique properties.Cavity mag-nomechanical system is a composite system composed of the microwave optical mode,the phonon mode,and the magnon mode.Quantum manipulation in cavity magnomechani-cal system is an important research object in basic physics applications,such as quantum information processing,ultra-high-precision metrology,and mechanical squeezing.How-ever,owing to the inevitable interaction with the thermal environment,the implementation of these applications may be destroyed.In order to suppress the uncontrollable thermal fluctuations,it is necessary to cool magnon resonator to the quantum ground state and many schemes of the ground state cooling of the magnon resonator have been proposed both in theoretically and experimentally.Among these studies,according to the relation-ship between the decay tate of cavity field and the magnon resonator frequency,it can be roughly divided into two categories,namely,the resolved sideband(?b>>ka)cooling and the unresolved sideband(?b<<ka)cooling.In this thesis,the ground-state cooling of the macroscopic magnomechanical resonator in the cavity magnomechanical system is studied under the limit of resolved sideband.And the main contents are as follows:Based on the parity-time(PT)symmetrical cavity magnomechanical system,we study the ground state cooling of the magnon resonator.In this scheme,the PT sym-metrical cavity magnomechanical system is composed of a loss yttrium iron garnet(YIG)sphere and a gain microwave cavity.Using the magnetic noise spectrum,we investi-gate the ground state cooling of the magnon resonator under the weak coupling regime(G<<ka)in PT symmetrical and non-PT symmetrical systems.It is found that the originally smoother Lorentz single-peak of the magnetic noise spectrum is significantly enhanced in PT symmetrical cavity magnomechanical system.However,the originally smoother Lorentz single-peak splits into a valley and two peaks in the non-PT symmet-rical cavity magnomechanical system.By comparing the magnetic noise spectrum of the two systems,we can find that ground state cooling of the magnon resonator is more obvious in the PT symmetrical cavity magnomechanical system.And the net cooling rate is significantly enhanced by four orders of magnitude.The rate equation is also used to solve the analytical expression of the final average number of phonons in the steady state,and the ground-state cooling of the magnon resonator is studied by selecting exper-imentally feasible parameters.The research results show that the ground state cooling of the magnon resonator can be achieved even under the conditions of the weak coupling regime.It is important to point out that this solution can directly achieve the ground state cooling of the magnon resonator at room temperature.In addition,an external magnetic field is also used to flexibly control the ground-state cooling of the magnon resonator.