Incorrect results from simulation of inverse controlled swap gate

[hvenev-insait]

Informations

• Qiskit Aer version: 0.17
• Python version: 3.13.3
• Operating system: Fedora 42

What is the current behavior?

The inverse-controlled swap gate qiskit.circuit.library.SwapGate().control(1, ctrl_state=0) is simulated incorrectly. It appears that an X gate is applied to the first target qubit before and after the gate (a in the example below).

Steps to reproduce the problem

import qiskit
import qiskit_aer

ctl = qiskit.QuantumRegister(1, name='ctl')
a = qiskit.QuantumRegister(1, name='a')
b = qiskit.QuantumRegister(1, name='b')

qc = qiskit.QuantumCircuit(ctl, a, b)

# Set up superposition
qc.h(ctl)
qc.h(a)

# First do an negated controlled swap:
#   negctrl @ swap ctl, a, b
qc.append(qiskit.circuit.library.SwapGate().control(1, ctrl_state=0), [ctl, a, b])

# Then do an negated controlled swap again, this time inverting the control with X gates:
#   x ctl; ctrl @ swap ctl, a, b; x ctl
qc.x(ctl)
qc.cswap(ctl, a, b)
qc.x(ctl)

# Undo setting up superposition
qc.h(a)
qc.h(ctl)

qc.save_statevector()

sim = qiskit_aer.AerSimulator(method='statevector', precision='double', device='CPU')
res = sim.run(qc, shots=1).result()
sv = res.data()['statevector']

print(qc)
print(list(sv))
assert abs(sv[0]) > 0.999

The issue seems to affect multiple simulation methods, not just statevector.

What is the expected behavior?

The assertion should pass: the block labelled (2) exactly undoes the block labelled (1).

Suggested solutions

Fix the simulation so that it interprets the inverse-controlled swap gate correctly.