Geometric phase for mixed states
L. C. Kwek, D. M. Tong, J. L. Chen, Jiangfeng Du, Keng Wah Choo, Ravishankar Ramanathan, Dagomir Kaszlikowski, C. H. Oh · Laser Physics · 2006
We present a kinematic approach for obtaining the geometric phase of a mixed state under nonunitary evolution. This phase is gauge-invariant and measurable and leads to well-known results for unitary evolution.