Potential Bug with QiskitAer simulating statevector for qiskit quantum circuit

[yangcal]

Informations

• Qiskit Aer version:0.15.1
• Python version:3.12
• Operating system:linux

What is the current behavior?

For a fixed QuantumCircuit with custom unitary gate matrix, QiskitAer is producing different statevector simulation results for qiskit v.1.2.4 and v.1.3.0

Steps to reproduce the problem

Using qiskit-aer=0.15.1, run the following script with qiskit==1.2.4 and qiskit==1.3.0 will reproduce different statevector results

import qiskit

from qiskit_aer import AerSimulator
from qiskit.circuit.library import UnitaryGate
from qiskit.quantum_info import random_unitary

import numpy as np

def get_qiskit_unitary_gate(rng, control=None):
    rand_unitary = random_unitary(4, seed=rng)
    gate = UnitaryGate(rand_unitary)
    print(f"unitary gate matrix:")
    print(gate)
    if control is None:
        return gate
    else:
        return gate.control(control)
    
def get_qiskit_multi_control_circuit():
    qubits = qiskit.QuantumRegister(5)
    circuit = qiskit.QuantumCircuit(qubits)
    for q in qubits:
        circuit.h(q)
    qs = list(qubits)

    rng = np.random.default_rng(1234)
    for i in range(2):
        rng.shuffle(qs)
        ccu_gate = get_qiskit_unitary_gate(rng, control=2)
        print(f"{i}th gate on {qs}")
        circuit.append(ccu_gate, qs[:4])
    circuit.p(0.1, qubits[0])
    return circuit

print(f"{qiskit.__version__=}")

circuit = get_qiskit_multi_control_circuit()
print(circuit)

circuit.save_statevector()

# Transpile for simulator
simulator = AerSimulator(method='statevector')
circ = qiskit.transpile(circuit, simulator)

# Run and get statevector
result = simulator.run(circ).result()
sv = np.asarray(result.get_statevector(circ))
print("Sum of state vector:", sv.sum())

What is the expected behavior?

The gate matrices defining the custom unitary gates are identical between qiskit==1.2.4 and qiskit==1.3.0 and therefore the returned statevector should be the same. On my end I have the following results:

qiskit==1.2.4

qiskit.__version__='1.2.4'
unitary gate matrix:
Instruction(name='unitary', num_qubits=2, num_clbits=0, params=[array([[ 0.26093746+0.18318812j,  0.12558674-0.38936694j,
         0.56486648-0.53659333j, -0.03587912+0.35025885j],
       [-0.5208327 +0.41955884j,  0.38293134-0.20373037j,
        -0.26997299-0.01611016j,  0.47100825+0.26375647j],
       [-0.18047959-0.0114164j ,  0.42182388+0.05310412j,
         0.01892911-0.48459796j, -0.10334574-0.73530097j],
       [-0.44557601+0.46884564j, -0.63238151+0.25262043j,
         0.15882664-0.24378088j, -0.17446941-0.05317653j]])])
0th gate on [Qubit(QuantumRegister(5, 'q1'), 0), Qubit(QuantumRegister(5, 'q1'), 4), Qubit(QuantumRegister(5, 'q1'), 1), Qubit(QuantumRegister(5, 'q1'), 3), Qubit(QuantumRegister(5, 'q1'), 2)]
unitary gate matrix:
Instruction(name='unitary', num_qubits=2, num_clbits=0, params=[array([[-0.41490662-0.1027918j , -0.45229939-0.45892536j,
         0.1965442 +0.27907236j,  0.53283662+0.04090535j],
       [-0.54960898-0.38886747j, -0.18060452+0.35532657j,
        -0.42299907-0.41452735j,  0.00811512+0.19238008j],
       [-0.48710529+0.16105765j,  0.30802545-0.50934349j,
         0.16188328-0.37911161j, -0.36497996-0.28166686j],
       [ 0.16591044+0.27066769j,  0.26600357-0.02948626j,
         0.10303047-0.5934482j ,  0.6357136 +0.24628756j]])])
1th gate on [Qubit(QuantumRegister(5, 'q1'), 1), Qubit(QuantumRegister(5, 'q1'), 4), Qubit(QuantumRegister(5, 'q1'), 2), Qubit(QuantumRegister(5, 'q1'), 0), Qubit(QuantumRegister(5, 'q1'), 3)]                      
Sum of state vector: (3.450103311811794-0.308774856832824j)

qiskit==1.3.0

qiskit.__version__='1.3.0'
unitary gate matrix:
Instruction(name='unitary', num_qubits=2, num_clbits=0, params=[array([[ 0.26093746+0.18318812j,  0.12558674-0.38936694j,
         0.56486648-0.53659333j, -0.03587912+0.35025885j],
       [-0.5208327 +0.41955884j,  0.38293134-0.20373037j,
        -0.26997299-0.01611016j,  0.47100825+0.26375647j],
       [-0.18047959-0.0114164j ,  0.42182388+0.05310412j,
         0.01892911-0.48459796j, -0.10334574-0.73530097j],
       [-0.44557601+0.46884564j, -0.63238151+0.25262043j,
         0.15882664-0.24378088j, -0.17446941-0.05317653j]])])
0th gate on [Qubit(QuantumRegister(5, 'q1'), 0), Qubit(QuantumRegister(5, 'q1'), 4), Qubit(QuantumRegister(5, 'q1'), 1), Qubit(QuantumRegister(5, 'q1'), 3), Qubit(QuantumRegister(5, 'q1'), 2)]
unitary gate matrix:
Instruction(name='unitary', num_qubits=2, num_clbits=0, params=[array([[-0.41490662-0.1027918j , -0.45229939-0.45892536j,
         0.1965442 +0.27907236j,  0.53283662+0.04090535j],
       [-0.54960898-0.38886747j, -0.18060452+0.35532657j,
        -0.42299907-0.41452735j,  0.00811512+0.19238008j],
       [-0.48710529+0.16105765j,  0.30802545-0.50934349j,
         0.16188328-0.37911161j, -0.36497996-0.28166686j],
       [ 0.16591044+0.27066769j,  0.26600357-0.02948626j,
         0.10303047-0.5934482j ,  0.6357136 +0.24628756j]])])
1th gate on [Qubit(QuantumRegister(5, 'q1'), 1), Qubit(QuantumRegister(5, 'q1'), 4), Qubit(QuantumRegister(5, 'q1'), 2), Qubit(QuantumRegister(5, 'q1'), 0), Qubit(QuantumRegister(5, 'q1'), 3)]                        
Sum of state vector: (2.6579282427026834+2.2212546524499133j)

From our experiment, I believe the results from qiskit=1.2.4 are correct. There might be some parsing issue between qiskit-aer and qiskit==1.3.0

Suggested solutions