Catalyst treats a density matrix measurement as a state measurement

[albi3ro]

Issue description

Description of the issue - include code snippets and screenshots here if relevant. You may use the following template below

• Expected behavior: (What you expect to happen)

I would the expect the same behavior as in a non-qjit execution. Requesting qml.density_matrix(wires) should return a density matrix.

Without the qjit, I get:

array([[0.46939564+0.j        , 0.        +0.11985638j,
        0.46939564+0.j        , 0.        +0.11985638j],
       [0.        -0.11985638j, 0.03060436+0.j        ,
        0.        -0.11985638j, 0.03060436+0.j        ],
       [0.46939564+0.j        , 0.        +0.11985638j,
        0.46939564+0.j        , 0.        +0.11985638j],
       [0.        -0.11985638j, 0.03060436+0.j        ,
        0.        -0.11985638j, 0.03060436+0.j        ]])

• Actual behavior: (What actually happens)

We just get the state.

• Reproduces how often: (What percentage of the time does it reproduce?)

Every time I execute it.

• System information: (post the output of import pennylane as qml; qml.about())

master pennylane, recent catalyst

Source code and tracebacks

dev = qml.device('lightning.qubit', wires=2)

@qml.qjit
@qml.qnode(dev)
def circuit(phi):
    qml.Hadamard(0)
    qml.IsingXX(phi, wires=(0,1))
    return qml.density_matrix(wires=(0,1))

circuit(0.5)

array([0.68512454+0.j        , 0.        -0.17494102j,
       0.68512454+0.j        , 0.        -0.17494102j])

Please include any additional code snippets and error tracebacks related to the issue here.

Additional information

Any additional information, configuration or data that might be necessary to reproduce the issue.