Thermal equilibrium density matrix.

sigma = sigeq(Ham,Temp)
sigma = sigeq(Ham,Temp,'pol')

This function calculates the thermal equilibrium density matrix for the system described by the Hamiltonian Ham (in units of MHz) for the temperature Temp (in units of K).

If 'pol' is given as a third argument, only the polarisation part of the thermal equilibrium density matrix is returned.

The returned density matrix sigma is in the same basis as Ham.

This is a straightforward implementation of

ham