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?(adsbygoogle = window.adsbygoogle || []).push({});

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Density matrix off-diagonal elements

**Physics Forums | Science Articles, Homework Help, Discussion**