Environment

• Qiskit Terra version:
  'qiskit-terra': '0.19.1'
  'qiskit': '0.33.1'
• Python version:
  3.9.7
• Operating system:
  Windows 10 Pro

What is happening?

I'm trying to implement a Parametric Hadamard Test.

I have already my parametric evolution gate exp(−iθH) where θ is the parameter.

When I defined the controlled-gate with Gate.control(1) and add it to the main circuit. I'm unable to correctly bind the parameters after and I can not get the state vector after the binded circuit.

How can we reproduce the issue?

thetas = ParameterVector('T', length=1)
it = iter(theta)

# Define Hadamard Test
qc = QuantumCircuit(3)
qc.initialize(psi_0, [1,2])

qc.h(0)

# Apply control gate

tr_g_k = tr_g(dt=next(it))  # tr_g is the evolution gate $\exp(-i\theta H)$
tr_g_c = tr_g_k.control(1)

qc.append(tr_g_c, [0,1,2])

qc.h(0)
# --------------------------------------------------------
# Get the StateVector

qc_b = qc.bind_parameters({theta: [np.pi]})

simulator = Aer.get_backend('aer_simulator')

qc_bt = transpile(qc_b, simulator)

qc_bt.save_statevector()

result = simulator.run(qc_bt).result()
statevector = result.get_statevector(qc_bt)

When running the circuit I get:

TypeError: ParameterExpression with unbound parameters ({ParameterVectorElement(T[0])}) cannot be cast to a float.

I have tried without the control, i.e, only the evolution in the qubit 1 and 2 and it works. I think it's because the control, but so far, I have not been able to solve it.

I tried .with the to_matrix() method of CircuitStateFn of Opflow, and I get the same error.

What should happen?

The circuit should bind the parameres correctly and it should give me the statevector at the end.

Any suggestions?

No response