How to calculate state fidelity in Qiskit?

Question

I have a circuit with different structures, now I'm trying to calculate the fidelity between those with the original one. How do I calculate the fidelity? I want also to initialize the state vector by myself. Can someone show how to compute fidelity for the below example?

For example if I have a circuit like below,

q = QuantumRegister(2)
qc = QuantumCircuit(q)
qc.cu1(3*pi/4, q[0], q[1]);
print(qc)

and different structure

q = QuantumRegister(2)
qc = QuantumCircuit(q)
qc.h(q[0]);
qc.h(q[1]);
qc.cu1(3*pi/4, q[0], q[1]);
qc.h(q[0]);
qc.h(q[1]);
print(qc)

Answer 1

There is more information towards the end of the tutorial here but essentially how you do this is you run both circuits on the state_vector simulator and then you can use the function state_fidelity to work out the fidelity between the two states.

The code to do this should look something like this

from qiskit.quantum_info import state_fidelity

# set up qc1 and qc2

backend = Aer.get_backend('statevector_simulator')

sv1 = execute(qc1, backend).result().get_statevector(qc1)
sv2 = execute(qc2, backend).result().get_statevector(qc2)

print(state_fidelity(sv1, sv2))