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Do not unroll gates in basis in add_control (#13475) (#13528)
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* Do not unroll gates in basis

* add tests

* review comments

* Add reno

(cherry picked from commit 582070d)

Co-authored-by: Julien Gacon <[email protected]>
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@mergify @Cryoris
mergify[bot] and Cryoris authored Dec 5, 2024
1 parent 23f181c commit 1263d82
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Showing 3 changed files with 149 additions and 98 deletions.
202 changes: 110 additions & 92 deletions qiskit/circuit/add_control.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
"""Add control to operation if supported."""
from __future__ import annotations

from math import pi
from qiskit.circuit.exceptions import CircuitError
from qiskit.circuit.library import UnitaryGate
from qiskit.transpiler import PassManager
Expand Down Expand Up @@ -92,7 +93,6 @@ def control(
Raises:
CircuitError: gate contains non-gate in definition
"""
from math import pi

# pylint: disable=cyclic-import
from qiskit.circuit import controlledgate
Expand All @@ -101,22 +101,23 @@ def control(

q_control = QuantumRegister(num_ctrl_qubits, name="control")
q_target = QuantumRegister(operation.num_qubits, name="target")
q_ancillae = None # TODO: add
controlled_circ = QuantumCircuit(q_control, q_target, name=f"c_{operation.name}")
if isinstance(operation, controlledgate.ControlledGate):
original_ctrl_state = operation.ctrl_state
operation = operation.to_mutable()
operation.ctrl_state = None

global_phase = 0
if operation.name == "x" or (
isinstance(operation, controlledgate.ControlledGate) and operation.base_gate.name == "x"
):
controlled_circ.mcx(q_control[:] + q_target[:-1], q_target[-1], q_ancillae)
if operation.definition is not None and operation.definition.global_phase:
global_phase += operation.definition.global_phase

basis = ["p", "u", "x", "z", "rx", "ry", "rz", "cx"]

if operation.name in basis:
apply_basic_controlled_gate(controlled_circ, operation, q_control, q_target[0])
else:
basis = ["p", "u", "x", "z", "rx", "ry", "rz", "cx"]
if isinstance(operation, controlledgate.ControlledGate):
operation = operation.to_mutable()
operation.ctrl_state = None

unrolled_gate = _unroll_gate(operation, basis_gates=basis)
if unrolled_gate.definition.global_phase:
global_phase += unrolled_gate.definition.global_phase
Expand All @@ -130,87 +131,17 @@ def control(

for instruction in definition.data:
gate, qargs = instruction.operation, instruction.qubits
if gate.name == "x":
controlled_circ.mcx(q_control, q_target[bit_indices[qargs[0]]], q_ancillae)
elif gate.name == "rx":
controlled_circ.mcrx(
gate.definition.data[0].operation.params[0],
q_control,
q_target[bit_indices[qargs[0]]],
use_basis_gates=False,
)
elif gate.name == "ry":
controlled_circ.mcry(
gate.definition.data[0].operation.params[0],
q_control,
q_target[bit_indices[qargs[0]]],
q_ancillae,
mode="noancilla",
use_basis_gates=False,
)
elif gate.name == "rz":
controlled_circ.mcrz(
gate.definition.data[0].operation.params[0],
q_control,
q_target[bit_indices[qargs[0]]],
use_basis_gates=False,
)
continue
elif gate.name == "p":
from qiskit.circuit.library import MCPhaseGate

controlled_circ.append(
MCPhaseGate(gate.params[0], num_ctrl_qubits),
q_control[:] + [q_target[bit_indices[qargs[0]]]],
)
elif gate.name == "cx":
controlled_circ.mcx(
q_control[:] + [q_target[bit_indices[qargs[0]]]],
q_target[bit_indices[qargs[1]]],
q_ancillae,
)
elif gate.name == "u":
theta, phi, lamb = gate.params
if num_ctrl_qubits == 1:
if theta == 0 and phi == 0:
controlled_circ.cp(lamb, q_control[0], q_target[bit_indices[qargs[0]]])
else:
controlled_circ.cu(
theta, phi, lamb, 0, q_control[0], q_target[bit_indices[qargs[0]]]
)
else:
if phi == -pi / 2 and lamb == pi / 2:
controlled_circ.mcrx(
theta, q_control, q_target[bit_indices[qargs[0]]], use_basis_gates=True
)
elif phi == 0 and lamb == 0:
controlled_circ.mcry(
theta,
q_control,
q_target[bit_indices[qargs[0]]],
q_ancillae,
use_basis_gates=True,
)
elif theta == 0 and phi == 0:
controlled_circ.mcp(lamb, q_control, q_target[bit_indices[qargs[0]]])
else:
controlled_circ.mcp(lamb, q_control, q_target[bit_indices[qargs[0]]])
controlled_circ.mcry(
theta,
q_control,
q_target[bit_indices[qargs[0]]],
q_ancillae,
use_basis_gates=True,
)
controlled_circ.mcp(phi, q_control, q_target[bit_indices[qargs[0]]])
elif gate.name == "z":
controlled_circ.h(q_target[bit_indices[qargs[0]]])
controlled_circ.mcx(q_control, q_target[bit_indices[qargs[0]]], q_ancillae)
controlled_circ.h(q_target[bit_indices[qargs[0]]])
if len(qargs) == 1:
target = q_target[bit_indices[qargs[0]]]
else:
raise CircuitError(f"gate contains non-controllable instructions: {gate.name}")
if gate.definition is not None and gate.definition.global_phase:
target = [q_target[bit_indices[qarg]] for qarg in qargs]

apply_basic_controlled_gate(controlled_circ, gate, q_control, target)

if gate.definition is not None and gate.definition.global_phase and gate.name != "rz":
global_phase += gate.definition.global_phase

# apply controlled global phase
if global_phase:
if len(q_control) < 2:
Expand All @@ -228,6 +159,7 @@ def control(
new_ctrl_state = ctrl_state
base_name = operation.name
base_gate = operation

# In order to maintain some backward compatibility with gate names this
# uses a naming convention where if the number of controls is <=2 the gate
# is named like "cc<base_gate.name>", else it is named like
Expand All @@ -250,15 +182,101 @@ def control(
return cgate


def apply_basic_controlled_gate(circuit, gate, controls, target):
"""Apply a controlled version of ``gate`` to the circuit.
This implements multi-control operations for the following basis gates:
["p", "u", "x", "z", "rx", "ry", "rz", "cx"]
"""
num_ctrl_qubits = len(controls)

if gate.name == "x":
circuit.mcx(controls, target)

elif gate.name == "rx":
circuit.mcrx(
gate.definition.data[0].operation.params[0],
controls,
target,
use_basis_gates=False,
)
elif gate.name == "ry":
circuit.mcry(
gate.definition.data[0].operation.params[0],
controls,
target,
mode="noancilla",
use_basis_gates=False,
)
elif gate.name == "rz":
circuit.mcrz(
gate.definition.data[0].operation.params[0],
controls,
target,
use_basis_gates=False,
)
# continue
elif gate.name == "p":
from qiskit.circuit.library import MCPhaseGate

circuit.append(
MCPhaseGate(gate.params[0], num_ctrl_qubits),
controls[:] + [target],
)
elif gate.name == "cx":
circuit.mcx(
controls[:] + [target[0]], # CX has two targets
target[1],
)
elif gate.name == "u":
theta, phi, lamb = gate.params
if num_ctrl_qubits == 1:
if theta == 0 and phi == 0:
circuit.cp(lamb, controls[0], target)
else:
circuit.cu(theta, phi, lamb, 0, controls[0], target)
else:
if phi == -pi / 2 and lamb == pi / 2:
circuit.mcrx(theta, controls, target, use_basis_gates=True)
elif phi == 0 and lamb == 0:
circuit.mcry(
theta,
controls,
target,
use_basis_gates=True,
)
elif theta == 0 and phi == 0:
circuit.mcp(lamb, controls, target)
else:
circuit.mcp(lamb, controls, target)
circuit.mcry(
theta,
controls,
target,
use_basis_gates=True,
)
circuit.mcp(phi, controls, target)

elif gate.name == "z":
circuit.h(target)
circuit.mcx(controls, target)
circuit.h(target)

else:
raise CircuitError(f"Gate {gate} not in supported basis.")


def _gate_to_circuit(operation):
"""Converts a gate instance to a QuantumCircuit"""
if hasattr(operation, "definition") and operation.definition is not None:
return operation.definition
else:
qr = QuantumRegister(operation.num_qubits)
qc = QuantumCircuit(qr, name=operation.name)
qc.append(operation, qr)
return qc

qr = QuantumRegister(operation.num_qubits)
qc = QuantumCircuit(qr, name=operation.name)
qc.append(operation, qr)
return qc


def _unroll_gate(operation, basis_gates):
Expand Down
11 changes: 11 additions & 0 deletions releasenotes/notes/fix-mcrz-19d14a8d973a82cb.yaml
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
---
fixes:
- |
Fixed a bug in :meth:`.RZGate.control` for more than 1 control qubit, which used
an unnecessarily expensive decomposition.
Fixed `#13473 <https://github.com/Qiskit/qiskit/issues/13473>`__.
upgrade_circuits:
- |
The generic control method for gates now avoids attempting to translate gates
into a supported basis, if the gate is already supported. This can slightly change the
synthesis of the controlled gate, although it should not increase the two-qubit gate count.
34 changes: 28 additions & 6 deletions test/python/circuit/test_controlled_gate.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@
from qiskit.quantum_info.states import Statevector
import qiskit.circuit.add_control as ac
from qiskit.transpiler.passes import UnrollCustomDefinitions, BasisTranslator
from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager
from qiskit.converters.circuit_to_dag import circuit_to_dag
from qiskit.converters.dag_to_circuit import dag_to_circuit
from qiskit.quantum_info import Operator
Expand Down Expand Up @@ -1571,13 +1572,15 @@ def test_single_controlled_rotation_gates(self, gate, cgate):
uqc = dag_to_circuit(basis_translator.run(unroller.run(dag)))
self.log.info("%s gate count: %d", cgate.name, uqc.size())
self.log.info("\n%s", str(uqc))
# these limits could be changed
if gate.name == "ry":
self.assertLessEqual(uqc.size(), 32, f"\n{uqc}")

if gate.name in ["ry", "rx"]:
expected_cx = 8
elif gate.name == "rz":
self.assertLessEqual(uqc.size(), 43, f"\n{uqc}")
else:
self.assertLessEqual(uqc.size(), 20, f"\n{uqc}")
expected_cx = 4
else: # u1
expected_cx = 6

self.assertLessEqual(uqc.count_ops().get("cx", 0), expected_cx, f"\n{uqc}")

def test_composite(self):
"""Test composite gate count."""
Expand All @@ -1595,6 +1598,25 @@ def test_composite(self):
self.log.info("%s gate count: %d", uqc.name, uqc.size())
self.assertLessEqual(uqc.size(), 96, f"\n{uqc}") # this limit could be changed

def test_mcrz_complexity(self):
"""Test MCRZ is decomposed using the efficient MC-SU(2) algorithm.
Regression test of #13473.
"""
basis_gates = ["sx", "x", "rz", "ecr"]
pm = generate_preset_pass_manager(
optimization_level=3, basis_gates=basis_gates, seed_transpiler=12345
)

num_qubits = 6
angle = np.pi / 7
qc = QuantumCircuit(num_qubits)
qc.append(RZGate(angle).control(num_qubits - 1), qc.qubits)

isa_qc = pm.run(qc)

self.assertLessEqual(isa_qc.count_ops().get("ecr", 0), 40)


@ddt
class TestControlledStandardGates(QiskitTestCase):
Expand Down

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