论文标题
磁铁的量子布朗运动
Quantum Brownian Motion for Magnets
论文作者
论文摘要
磁性材料中的自旋进动通常是用经典现象学Landau-Lifshitz-Gilbert（LLG）方程进行建模的。基于量化的自旋+环境哈密顿量，我们在这里得出了一个通用的自旋操作者运动方程，该运动描述了三维进动和阻尼，并始终如一地说明了由记忆，有色噪声和量子统计量产生的影响。 LLG方程被恢复为经典的欧姆近似。我们进一步介绍了共鸣的Lorentzian系统 - 库库耦合，从而可以系统地比较欧姆和非欧摩型制度之间的动态。最后，我们模拟了半经典极限中自旋的完整非马克维亚动力学。在低温下，我们的数值结果表明，由环境的量子统计量引起的稳态旋转对准与外部场的特征降低和变平。结果为探索量子热力学中的一般三维耗散提供了强大的框架。
Spin precession in magnetic materials is commonly modelled with the classical phenomenological Landau-Lifshitz-Gilbert (LLG) equation. Based on a quantized spin+environment Hamiltonian, we here derive a general spin operator equation of motion that describes three-dimensional precession and damping and consistently accounts for effects arising from memory, coloured noise and quantum statistics. The LLG equation is recovered as its classical, Ohmic approximation. We further introduce resonant Lorentzian system--reservoir couplings that allow a systematic comparison of dynamics between Ohmic and non--Ohmic regimes. Finally, we simulate the full non-Markovian dynamics of a spin in the semi--classical limit. At low temperatures, our numerical results demonstrate a characteristic reduction and flattening of the steady state spin alignment with an external field, caused by the quantum statistics of the environment. The results provide a powerful framework to explore general three-dimensional dissipation in quantum thermodynamics.
