@misc{indiciae6e88185719e1,
  title = {Off-diagonal geometric phase for mixed states.},
  author = {Stefan Filipp and Erik Sjöqvist},
  year = {2003},
  doi = {10.1103/physrevlett.90.050403},
  url = {https://pubmed.ncbi.nlm.nih.gov/12633343/},
  note = {Source identifier: 12633343}
}