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Fix qpy for MCX gates #9391

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merged 5 commits into from
Jan 20, 2023
Merged

Fix qpy for MCX gates #9391

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4827256
Add MCXGrayCode
ElePT Jan 19, 2023
43fd417
Add test and reno
ElePT Jan 19, 2023
97a2f80
Add other mcx gates
ElePT Jan 20, 2023
642bbfa
Fix test
ElePT Jan 20, 2023
3ff5e00
Merge branch 'main' into qpy-bugfix
mergify[bot] Jan 20, 2023
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2 changes: 1 addition & 1 deletion qiskit/qpy/binary_io/circuits.py
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Expand Up @@ -252,7 +252,7 @@ def _read_instruction(file_obj, circuit, registers, custom_operations, version,
if gate_name in {"IfElseOp", "WhileLoopOp"}:
gate = gate_class(condition_tuple, *params)
elif version >= 5 and issubclass(gate_class, ControlledGate):
if gate_name in {"MCPhaseGate", "MCU1Gate"}:
if gate_name in {"MCPhaseGate", "MCU1Gate", "MCXGrayCode"}:
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I'm just curious if there are other gates in the mcx family that have the same constructor and need this. I always get lost in all the mcx variants. But it might be good to check we've got all of them covered here

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@ElePT ElePT Jan 19, 2023 •
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You were right @mtreinish, qpy also fails for other MCX gates. Namely (I think these are all):

MCXRecursive
MCXVChain
MCXGate

I can add these to the PR. I though I had tested it before realizing that I was using 2 control qubits, so the gate ended up being of type CCXGate (of course my checks passed).

gate = gate_class(*params, instruction.num_ctrl_qubits)
else:
gate = gate_class(*params)
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6 changes: 6 additions & 0 deletions releasenotes/notes/fix-qpy-mcxgray-421cf8f673f24238.yaml
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@@ -0,0 +1,6 @@
---
fixes:
- |
Fixed a bug in QPY (:mod:`qiskit.qpy`) where circuits containing gates of class
:class:`.MCXGrayCode` would fail to serialize.
See `#9390 <https://github.com/Qiskit/qiskit-terra/issues/9390>`__.
14 changes: 12 additions & 2 deletions test/python/circuit/test_circuit_load_from_qpy.py
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Expand Up @@ -24,7 +24,15 @@
from qiskit.circuit.quantumregister import Qubit
from qiskit.circuit.random import random_circuit
from qiskit.circuit.gate import Gate
from qiskit.circuit.library import XGate, QFT, QAOAAnsatz, PauliEvolutionGate, DCXGate, MCU1Gate
from qiskit.circuit.library import (
XGate,
QFT,
QAOAAnsatz,
PauliEvolutionGate,
DCXGate,
MCU1Gate,
MCXGrayCode,
)
from qiskit.circuit.instruction import Instruction
from qiskit.circuit.parameter import Parameter
from qiskit.circuit.parametervector import ParameterVector
Expand Down Expand Up @@ -1043,9 +1051,11 @@ def test_open_controlled_gate(self):

def test_standard_control_gates(self):
"""Test standard library controlled gates."""
qc = QuantumCircuit(3)
qc = QuantumCircuit(6)
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mcu1_gate = MCU1Gate(np.pi, 2)
mcx_gray_gate = MCXGrayCode(5)
qc.append(mcu1_gate, [0, 2, 1])
qc.append(mcx_gray_gate, list(range(0, 6)))
qc.mcp(np.pi, [0, 2], 1)
qc.mct([0, 2], 1)
qc.mcx([0, 2], 1)
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