Error when adding gate after circuit.initialize method

Environment

• Qiskit Terra version: 0.19.2
• Python version: 3.9.6
• Operating system: Windows 11

What is happening?

Failure to run quantum circuit after circuit.initialize() method and any gate, using either statevector or qasm simulator.

The circuit runs when only having an initialize method. But it fails when more gates are appended after the initialization.

How can we reproduce the issue?

beta = 0.3
alpha = np.sqrt(1 - abs(beta)**2)
qc = QuantumCircuit(1)
qc.initialize([alpha, beta], 0)
qc.h(0)
qc.measure_all()
qc.draw()

sv_sim = Aer.get_backend('statevector_simulator')
qasm_sim = Aer.get_backend('qasm_simulator')
execute(qc, qasm_sim).result().get_counts()

…

What should happen?

I would imagine we can initialize a state and apply any gate we want to it. Here, this code block should get a Python dictionary of measurement counts.

Any suggestions?

The second param of initialize() method can also be a bit misleading, causing ambiguity when reading the doc, since one may natively think “qubits” as the number of qubits. But I think I get the intention now.

[wyqian1027]

Could you try upgrading your version of Terra, and seeing if the bug persists? You’ve got a pretty old version (0.19.2) compared to the current 0.22.0.

(For what it’s worth, I ran this:

import numpy as np
from qiskit import QuantumCircuit, Aer, execute

beta = 0.3
alpha = np.sqrt(1 - abs(beta)**2)
qc = QuantumCircuit(1)
qc.initialize([alpha, beta], 0)
qc.h(0)
qc.measure_all()
qc.draw()

sv_sim = Aer.get_backend('statevector_simulator')
qasm_sim = Aer.get_backend('qasm_simulator')
execute(qc, qasm_sim).result().get_counts()

with Terra 0.22.0 and Aer 0.11.0 and got

{'1': 197, '0': 827}

which looks about right to me.)

Thanks a million, I will do so right away!

[jakelishman]

Could you try upgrading your version of Terra, and seeing if the bug persists? You’ve got a pretty old version (0.19.2) compared to the current 0.22.0.

(For what it’s worth, I ran this:

import numpy as np
from qiskit import QuantumCircuit, Aer, execute

beta = 0.3
alpha = np.sqrt(1 - abs(beta)**2)
qc = QuantumCircuit(1)
qc.initialize([alpha, beta], 0)
qc.h(0)
qc.measure_all()
qc.draw()

sv_sim = Aer.get_backend('statevector_simulator')
qasm_sim = Aer.get_backend('qasm_simulator')
execute(qc, qasm_sim).result().get_counts()

with Terra 0.22.0 and Aer 0.11.0 and got

{'1': 197, '0': 827}

which looks about right to me.)