密度演化算子在量子系综演化中的应用

Application of density evolution operator in quantum ensemble evolution

讨论在4种情况下,用量子系综密度演化算子描述量子系统状态,并证明了存在包含ρ支集中任一状态的最小系综,使这一状态以固定概率出现.最后证明了当密度算子为纯态时,Bloch向量的模为1;为混合态时,Bloch向量的模小于1.

The quantum system state described by quantum ensemble density evolution operator in four cases is discussed,and the existence of a minimal ensemble which includes any state of ρ support and makes the state appear in a fixed probability of piis proved.Finally,that the module of Bloch vector equals to 1 when the density operator is pure state,and the module of Bloch vector is less than 1 when the density operator is mixed state are also proved.