Informations

• Qiskit Aer version: 0.13.0
• Python version: 3.10.8
• Operating system:

What is the current behavior?

The following code returns {'0':1000} with Aer 0.13.0:

import numpy as np
from qiskit_aer import QasmSimulator
from qiskit import QuantumCircuit

qc = QuantumCircuit(1)
qc.ry(- np.pi / 2, 0)
qc.rz(0, 0)
qc.sx(0)
qc.rz(np.pi / 2, 0)
qc.sx(0)
qc.rz(0, 0)
qc.measure_all()
QasmSimulator().run(qc, shots=1000).result().get_counts()

The expected result would be {'1':1000}, which is what older versions of Aer return. Furthermore, if instead of qc.ry(np.pi/2,0) a small angle is added:

qc.ry(- np.pi / 2 + 0.000000001, 0)

the result is again correct. Alternatively, transpiling the circuit gives the correct result, but as far as I know, transpiling shouldn't be necessary to run on a QasmSimulator.