Add an example to the `to_openqasm` docs to show how to use the `wires` kwarg to avoid qubit reordering

[gsbgithub]

Expected behavior

The generated OpenQASM should preserve the wire ordering and gate semantics of the original PennyLane circuit.

Actual behavior

The exported OpenQASM remaps gate operands

Additional information

The OpenQASM generated by qml.to_openqasm() does not match the circuit definition for a simple 3-qubit circuit containing Pauli-X and Toffoli gates.

The circuit is defined as:

• Apply X on wire 0
• Apply X on wire 2
• Apply Toffoli with controls (0,1) and target (2)

However, the exported OpenQASM applies X on wire 1 instead of wire 2 and exports the Toffoli as ccx q[0],q[2],q[1],
which changes the circuit semantics.

Source code

import pennylane as qml
n_qubits = 3
dev = qml.device("default.qubit", wires=n_qubits)
@qml.qnode(dev)
def penny_qc():
  qml.X(0)
  qml.X(2)
  # controls = 0,1 ; target = 2
  qml.Toffoli(wires=[0, 1, 2])
  return qml.state()

# circuit structure
tape = qml.workflow.construct_tape(penny_qc)()
print("Operations:")
for op in tape.operations:
  print(op.name, list(op.wires))

print("\nCircuit:")
print(qml.draw(penny_qc)())

print("\nOpenQASM:")
qasm_str = qml.to_openqasm(penny_qc)()
print(qasm_str)


## Output:
## Operations


PauliX [0]
PauliX [2]
Toffoli [0, 1, 2]


## Circuit

0: ──X─╭●─┤
1: ────├●─┤
2: ──X─╰X─┤


## Generated OpenQASM


OPENQASM 2.0;
include "qelib1.inc";
qreg q[3];
creg c[3];

x q[0];
x q[1];
ccx q[0],q[2],q[1];

measure q[0] -> c[0];
measure q[1] -> c[1];
measure q[2] -> c[2];


## Expected OpenQASM


OPENQASM 2.0;
include "qelib1.inc";
qreg q[3];
creg c[3];

x q[0];
x q[2];
ccx q[0],q[1],q[2];

measure q[0] -> c[0];
measure q[1] -> c[1];
measure q[2] -> c[2];

Tracebacks

System information

Name: pennylane
Version: 0.45.1
Summary: PennyLane is a cross-platform Python library for quantum computing, quantum machine learning, and quantum chemistry. Train a quantum computer the same way as a neural network.
Home-page: 
Author: 
License: 
Location: F:\anaconda3\envs\qiskitenv\Lib\site-packages
Platform info:           Windows-10-10.0.19045-SP0
Python version:          3.11.5
Numpy version:           2.4.0
Scipy version:           1.16.3
JAX version:             None
Catalyst version:        None
Installed devices:
- default.clifford (pennylane-0.45.1)
- default.gaussian (pennylane-0.45.1)
- default.mixed (pennylane-0.45.1)
- default.qubit (pennylane-0.45.1)
- default.qutrit (pennylane-0.45.1)
- default.qutrit.mixed (pennylane-0.45.1)
- default.tensor (pennylane-0.45.1)
- null.qubit (pennylane-0.45.1)
- reference.qubit (pennylane-0.45.1)
- lightning.qubit (pennylane_lightning-0.45.0)
- qiskit.aer (PennyLane-qiskit-0.45.0)
- qiskit.basicaer (PennyLane-qiskit-0.45.0)
- qiskit.basicsim (PennyLane-qiskit-0.45.0)
- qiskit.remote (PennyLane-qiskit-0.45.0)

Existing GitHub issues

• I have searched existing GitHub issues to make sure the issue does not already exist.

[CatalinaAlbornoz]

Hi @gsbgithub , thanks for opening this report!

This behaviour is indeed confusing. Basically the operations are queued up in the order in which they appear so the X gate on the 2nd wire is moved to qubit 1 because it's the next available qubit. Many PennyLane features have a "wire_order" kwarg to avoid this confusion. For to_openqasm we don't have a "wire_order" kwarg but instead a wires kwarg. In your case you'd need to set wires=[0,1,2]. This is how you can use it:

qasm_str = qml.to_openqasm(penny_qc, wires=[0,1,2])()

I think it might be worth adding an example for this in the documentation for to_openqasm so I'll leave the issue open but I'll remove the bug label.

Thanks again for opening this issue and I hope my answer clarifies things for you!

[gsbgithub]

Thanks for the clarification.

…

On Tue, 7 Jul, 2026, 6:12 am Catalina Albornoz, ***@***.***> wrote: *CatalinaAlbornoz* left a comment (PennyLaneAI/pennylane#9768) <#9768 (comment)> Hi @gsbgithub <https://github.com/gsbgithub> , thanks for opening this report! This behaviour is indeed confusing. Basically the operations are queued up in the order in which they appear so the X gate on the 2nd wire is moved to qubit 1 because it's the next available qubit. Many PennyLane features have a "wire_order" kwarg to avoid this confusion. For to_openqasm we don't have a "wire_order" kwarg but instead a wires kwarg. In your case you'd need to set wires=[0,1,2]. This is how you can use it: qasm_str = qml.to_openqasm(penny_qc, wires=[0,1,2])() I think it might be worth adding an example for this in the documentation for to_openqasm so I'll leave the issue open but I'll remove the bug label. Thanks again for opening this issue and I hope my answer clarifies things for you! — Reply to this email directly, view it on GitHub <#9768?email_source=notifications&email_token=AK4QSVHHMD4SNMLIIMUSDKD5DRBPNA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOBZHA4TINBUHE4KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-4898944498>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AK4QSVGJ7UT3PSCCAWYD5VD5DRBPNAVCNFSNUABFKJSXA33TNF2G64TZHMYTEOJZGM3DGNRQHNEXG43VMU5TIOBQHA4DOOBXGA2KC5QC> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/AK4QSVA32Q3E3KKS5TZ6A4D5DRBPNA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOBZHA4TINBUHE4KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android <https://github.com/notifications/mobile/android/AK4QSVC33IBG47SYOEKYJQL5DRBPNA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIOBZHA4TINBUHE4KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you were mentioned.Message ID: ***@***.***>