Output Bloch vector

[quantumjim]

What is the expected behavior?

It would be good to have a tool that takes a single qubit circuit and outputs the corresponding Bloch vector.

I don't think this currently exists, and I don't think it fits with the philosophy of Terra. But perhaps it could go somewhere here in Ignis?

[mtreinish]

You can do this today pretty easily with terra. For example:

backend_sv_sim = qiskit.BasicAer.get_backend('statevector_simulator')
qr = qiskit.QuantumRegister(1)
cr = qiskit.ClassicalRegister(1)
circ = qiskit.QuantumCircuit(qr, cr)
circ.h(qr)
circ.sdg(qr)
result = qiskit.execute(circ, backend_sv_sim).result()
qiskit.visualization.plot_bloch_multivector(result.get_statevector())

(I just copy and pasted that from the qiskit workshop I've given in the past)

which returns:

[quantumjim]

Thanks.

I think that only works for the statevector simulator, does it not. For the qasm simulator or real devices, one needs to implement x, y and z measurements and process and combine the results.

[mtreinish]

Yes, that's true, I didn't realize that's what you were talking about. I just assumed you wanted to go from an arbitrary circuit to a bloch vector. But yeah if you're running on a real device or using the qasm simulator you'll have to do more analysis to get that. It definitely feels like ignis would be the right place to do that.

[dcmckayibm]

You could loop it in with the tomography code, but I would just make it as a notebook example