热辐射场中四能级原子的量子相干性

原子与辐射场的相互作用,引起原子能量耗散或相对位相改变,导致原子由相干叠加态退化为混合态。该文针对四能级原子辐射和吸收情况,基于Kraus算子理论,利用约化密度矩阵方法,得到四能级原子密度矩阵元的演化规律,从而研究原子的量子相干特性。研究表明:初态处于相干叠加态的四能级原子,由于辐射和吸收,可能演化成相干叠加态、未完全混合态、完全混合态或单一纯态。

The Four-level Atomic Quantum Coherence in Thermal Radiation Field

The interactions between atoms and the radiation field lead to atoms energy dissipation or phase change,and eventually cause atoms degenerate from coherent superposition states into mixed states.This thesis analyzed the four-level atom radiation and absorption and using the reduced density matrix method to obtain the evolution of the four-level atom density matrix elements based on quantum mechanics and Kraus operator theory.According to these theoretical analysis,we draw the conclusion that the four-level atoms with a initial state of coherent superposition can evolved into coherent superposition state,noncompletely mixed state and completely mixed state or single vector state.