- #1
auctor
- 8
- 0
The possible values of the diagonal elements of a density matrix are restricted by the condition [itex] \mathrm{Tr}~\rho = 1 [/itex]. Are there any restrictions on the possible values of off-diagonal elements, apart from the obvious [itex] \mathrm{Re}~\rho_{nm} = \mathrm{Re}~\rho_{mn}[/itex], [itex] \mathrm{Im}~\rho_{nm} = - \mathrm{Im}~\rho_{mn}[/itex]? If the off-diagonals are written in the form [itex] \left| \rho_{nm} \right| \exp{i \phi_{nm}} [/itex], do the absolute value and the phase have a simple physical meaning?