Density matrices as polarization vectors

  title={Density matrices as polarization vectors},
  author={Ugo Fano},
  journal={Rendiconti Lincei},
  • U. Fano
  • Published 1 June 1995
  • Physics
  • Rendiconti Lincei
The concept of a density matrix originated about 1930 in the process of adapting to quantum mechanics the statistical descriptions of classical phenomena. A new light was cast on this concept when Felix Bloch formulated his NMR equation, inclusive of dissipative terms: This equation, ostensibly the time-dependent Schrödinger equation for a spin’s density matrix, governs in fact the expectation values of evolving observables, namely, the components of the spin’s polarization vector. It serves… 

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