Reference Section Method for Mixed State Geometric Phase in Nonunitary Evolution* *Supported in part by the Natural Science Foundation of China under Grant Nos. 10821504, 11075194, 11135003, 11275246, and 11475238, and by the National Basic Research Program of China (973 Program) under Grant No. 2010CB833000 (TL)

Abstract

We propose the reference section method to obtain a geometric phase for the mixed states in nonunitary evolution. The reference connection on density operator space is defined. That the parallel transport method and reference section method are essentially two aspects of in phase concept is pointed out.