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Fix post-oxidization change in ConsolidateBlocks behavior #13450

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merged 4 commits into from
Nov 18, 2024
Merged

Fix post-oxidization change in ConsolidateBlocks behavior #13450

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caba840
Set decomposer to None if kak_gates not found during ConsolidateBlock…
ElePT Nov 18, 2024
67b9530
Add test that reproduces issue
ElePT Nov 18, 2024
e3124a6
Re-add rzz to list of kak gates
ElePT Nov 18, 2024
3238a61
Add path for rzx gate.
ElePT Nov 18, 2024
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12 changes: 9 additions & 3 deletions qiskit/transpiler/passes/optimization/consolidate_blocks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,9 +12,11 @@

"""Replace each block of consecutive gates by a single Unitary node."""
from __future__ import annotations
from math import pi

from qiskit.synthesis.two_qubit import TwoQubitBasisDecomposer
from qiskit.circuit.library.standard_gates import CXGate, CZGate, iSwapGate, ECRGate
from qiskit.circuit.library.standard_gates import CXGate, CZGate, iSwapGate, ECRGate, RXXGate

from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler.passmanager import PassManager
from qiskit._accelerate.consolidate_blocks import consolidate_blocks
Expand All @@ -27,6 +29,7 @@
"cz": CZGate(),
"iswap": iSwapGate(),
"ecr": ECRGate(),
"rxx": RXXGate(pi / 2),
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why is the angle here fixed to pi/2 ?

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It's because that's what UnitarySynthesis uses if it's a basis_gates only setup: https://github.com/Qiskit/qiskit/blob/main/qiskit/transpiler/passes/synthesis/unitary_synthesis.py#L98 the idea is that it's trying to match the decomposer used for estimating to what the synthesis pass will use later.

The whole logic between the passes is more than a bit hacky. ConsolidateBlocks tries to guess how many 2q gates will be used to decide whether to consolidate the block into a unitary or not. This is strongly coupled to the behavior of UnitarySynthesis because that's what actually does the synthesis later. But none of this actually takes into account multiple possible decomposers/synthesis methods being supported by a target, or the presence of a non-default plugin being used.

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FWIW, I did some testing locally with this and in some cases using TwoQubitBasisDecomposer(RXXGate(pi/2)) under estimates what the XXDecomposer estimates, 3 vs 4 gates. This might result in some blocks not getting consolidated which were before, but in practice I find it probably pretty unlikely since it only counts rzz gates when evaluating if the block's gates are more than the expected synthesis output.

}


Expand Down Expand Up @@ -70,7 +73,6 @@ def __init__(
if basis_gates is not None:
self.basis_gates = set(basis_gates)
self.force_consolidate = force_consolidate

if kak_basis_gate is not None:
self.decomposer = TwoQubitBasisDecomposer(kak_basis_gate)
elif basis_gates is not None:
Expand All @@ -79,8 +81,12 @@ def __init__(
self.decomposer = TwoQubitBasisDecomposer(
KAK_GATE_NAMES[kak_gates.pop()], basis_fidelity=approximation_degree or 1.0
)
elif "rzx" in basis_gates:
self.decomposer = TwoQubitBasisDecomposer(
CXGate(), basis_fidelity=approximation_degree or 1.0
)
else:
self.decomposer = TwoQubitBasisDecomposer(CXGate())
self.decomposer = None
else:
self.decomposer = TwoQubitBasisDecomposer(CXGate())

Expand Down
29 changes: 24 additions & 5 deletions test/python/transpiler/test_consolidate_blocks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,20 +16,19 @@

import unittest
import numpy as np
from ddt import ddt, data

from qiskit.circuit import QuantumCircuit, QuantumRegister, IfElseOp, Gate
from qiskit.circuit.library import U2Gate, SwapGate, CXGate, CZGate, UnitaryGate
from qiskit.converters import circuit_to_dag
from qiskit.transpiler.passes import ConsolidateBlocks
from qiskit.quantum_info.operators import Operator
from qiskit.quantum_info.operators.measures import process_fidelity
from qiskit.transpiler import PassManager
from qiskit.transpiler import Target
from qiskit.transpiler.passes import Collect1qRuns
from qiskit.transpiler.passes import Collect2qBlocks
from qiskit.transpiler import PassManager, Target, generate_preset_pass_manager
from qiskit.transpiler.passes import ConsolidateBlocks, Collect1qRuns, Collect2qBlocks
from test import QiskitTestCase # pylint: disable=wrong-import-order


@ddt
class TestConsolidateBlocks(QiskitTestCase):
"""
Tests to verify that consolidating blocks of gates into unitaries
Expand Down Expand Up @@ -571,6 +570,26 @@ def __init__(self):

self.assertEqual(res, qc)

@data(2, 3)
def test_no_kak_gates_in_preset_pm(self, opt_level):
"""Test correct initialization of ConsolidateBlocks pass when kak_gates aren't found.
Reproduces https://github.com/Qiskit/qiskit/issues/13438."""

qc = QuantumCircuit(2)
qc.cz(0, 1)
qc.sx([0, 1])
qc.cz(0, 1)

ref_pm = generate_preset_pass_manager(
optimization_level=1, basis_gates=["rz", "rzz", "sx", "x", "rx"]
)
ref_tqc = ref_pm.run(qc)
pm = generate_preset_pass_manager(
optimization_level=opt_level, basis_gates=["rz", "rzz", "sx", "x", "rx"]
)
tqc = pm.run(qc)
self.assertEqual(ref_tqc, tqc)


if __name__ == "__main__":
unittest.main()