I am trying to implement the quantum teleportation protocol from the qiskit textbook in qiskit: I start with q_0 bit = 1 and I expect that q_3 = 1 at the end but it does not work.
from qiskit import *
qc = QuantumCircuit(3, 3)
qc.x(0) #q -> 1
qc.barrier()
qc.h(1)
qc.cx(1, 2)
qc.barrier()
# Next, apply the teleportation protocol.
qc.cx(0, 1)
qc.h(0)
qc.barrier()
# We measure these qubits and use the classical results to perform an operation
qc.measure(0, 0)
qc.measure(1, 1)
qc.cx(1, 2)
qc.cz(0, 2)
#qc.barrier()
backend = Aer.get_backend('qasm_simulator')
job = execute(qc, backend, shots=1, memory=True).result()
result = job.get_memory()[0]
qc.measure(2, 2)
print(job.get_memory()[0]) #q = 0
It looks like it is working as intended. In the textbook, it says towards the end of the code cell:
In principle, if the teleportation protocol worked, we have q[2] = secret_unitary|0> As a result, we should be able to recover q[2] = |0> by applying the reverse of secret_unitary since for a unitary u, u^dagger u = I.
You had your secret_unitary as 'x', which does in fact change Alice's first qubit to 1. But, at the end of the circuit, the dagger of the secret_unitary is applied, cancelling the original application of the secret_unitary. You should expect to see 0 for q[2], as that means that the state from q[0] (in this case, 1) was successfully teleported to q[2], and then brought back to 0 by the dagger of the secret_unitary.