How to convert from choi to chi matrix in qiskit

Question

I have done a quantum process tomography experiment on a two qubit system.

# Set up the QPT experiment
qpt = ProcessTomography(qc_h)

#Run
qstdata1 = qpt.run(backend, shots=(1024*2)).block_for_results()

#Result
for result in qstdata1.analysis_results():
    print(result)

The output contains a Choi matrix:

AnalysisResult
- name: state
- value: Choi([[ 0.52176658+0.00000000e+00j,  0.46669301-3.60389531e-03j,
        0.45464147-2.22373925e-02j, -0.45936069+1.54147696e-02j],
      [ 0.46669301+3.60389531e-03j,  0.47843409+1.30104261e-18j,
        0.47397839+1.01701620e-02j, -0.45466925+2.23604672e-02j],
      [ 0.45464147+2.22373925e-02j,  0.47397839-1.01701620e-02j,
        0.49722515+0.00000000e+00j, -0.47223203+1.56516697e-02j],
      [-0.45936069-1.54147696e-02j, -0.45466925-2.23604672e-02j,
       -0.47223203-1.56516697e-02j,  0.50257418+0.00000000e+00j]],
     input_dims=(2,), output_dims=(2,))

However, I would like it to be a Chi ($\chi$) matrix so I can plot it.

How do I go about turning that data above, from a Choi matrix, to a Chi matrix?

Cheers

Answer 1

The constructor of Chi class accepts an instance of Choi. So, if _choi is your Choi matrix, you can get Chi matrix by simply calling Chi(_choi)

from qiskit.quantum_info import Chi

_chi = Chi(_choi)