自旋波与微波强耦合的量子理论

自旋波与微波之间的强耦合作用是近年来自旋领域的一个新兴研究方向。在理论研究中，大多数研究采用基于朗道-栗夫史兹方程和麦克斯韦方程组的唯象方法。这一方法在解释光子反馈系统的自旋波五重态等现象时存在较大困难，同时它不能拓展到超低温下的量子极限情况，因而发展量子理论就显得极为必要。本项目拟从以下几个方面开展研究：（1）建立能级吸引的正确的哈密顿量，揭示其背后的物理机理，研究本征态、含时演化与量子极限行为；（2）研究光子反馈机制下的反馈光子与微波腔之间的相互作用，发展新的理论方法来研究五重态的本征能与线宽；（3）发展强驱动下无平均场近似的双稳定性理论，研究涨落对双稳定性的影响以及量子极限行为；（4）建立非线性耦合哈密顿量，研究非线性耦合对于能谱和线宽的影响；通过本项目的研究，预期在能级吸引、光子反馈、强驱动和非线性耦合等物理现象上获得更新的理解，并预测更多的物理现象，发展更多的理论方法。

Recently, strong coupling between spin wave and microwave has attracted considerable attraction in the field of spintronics. In theoretical studies, the method used generally is the phenomenological Landau-Lifshitz-Gilbert equation and the Maxwell's equations. This method is hard to explain many experimental observation, such as the occurrence of magnon quintuplet in feedback-coupled cavities. Moreover, it can not be extended to the quantum limit at ultralow temperature, which makes the development of quantum theory very necessary. Motivated by these problems, we are intending to carry out systematic studies in the following subjects. First, the Hamiltonian of level attraction in the cavity magnon polariton will be set and the underlying physical mechanism will be revealed. The eigenstate, temporal dynamics and quantum limit behavior will be studied. Second, the interaction between microwave cavity and feedback cavity will be studied. New theory and computational methods will be developed for the building and diagonalization of the Hamiltonian and line-width calculation. Third, we will develop theory and numerical method to study bistability of cavity magnon polariton in the absence of mean field approximation. The effect of fluctuation on magnon bistability and the quantum limit behavior will be studied. Finally, the Hamiltonian of nonlinear magnon-photon coupling will be built in and the effect of nonlinear coupling on spectrum and line-width will be studied. After completing this proposal, we expect that new understanding on the existing theoretical and experimental results, e.g. the level attraction, photon feedback, strong driving and nonlinear coupling, will be obtained. Moreover, some new behavior will be predicted and new theory and method will be developed for future studies.