For the QuTip backend it would be helpful to get the density matrix of multiple qubits and not just one

[stephendiadamo]

In the QuTip backend, current the the density_operator method takes one qubit at a time. This prevents getting the density matrix of a joint system. This can be easily modified to get the density matrix for a list of qubits which would make it more useful.

[stephendiadamo]

In development is the branch density-matrix. I'm not able to test at the moment due to Qutip installation problems. Will come back to it.