@misc{indiciaee0804903c381,
  title = {Density matrix and entropies for electromagnetic fields.},
  author = {IA Levín and D Otero and AN Proto},
  year = {1989},
  doi = {10.1103/physreva.40.5998},
  url = {https://pubmed.ncbi.nlm.nih.gov/9901977/},
  note = {Source identifier: 9901977}
}