Thermal density matrix

[mahmoud mohammadi]

 Hi Dear Group Members, I would like calculate  the Thermal density matrix for atom-cavity system with a specific Hamiltonian, but the Thermal density matrix in QUTIP is written based on an oscillator Hamiltonian while my Hamiltonian is different. How do I get a Thermal density matrix with another Hamiltonian? Thanks

[Simon Cross]

Hi Mahmoud,

Are you referring to `qutip.states.thermal_dm`? If so, I think the
answer depends on what your different Hamiltonian is. One option for a
general Hamiltonian is that you could evolve your system from an
initial density matrix to a steady state.

Yours sincerely,
Simon Cross

[Neill Lambert]

Just to add to what simon said, I guess you can also  do by hand with something like

energies, states = H.eigenstates()
rhoss = 0.
for kk, energ in enumerate(energies):
    rhoss += (states[kk]*states[kk].dag()*np.exp(-beta*energies[kk])) 

rhoss = rhoss/rhoss.norm()

where beta is the inverse temperature, and H is the qubit + cavity hamiltonian

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