From c7e397f65a09d06ab41beda27ce702fb1f0db303 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Pablo=20Le=20H=C3=A9naff?= Date: Fri, 23 Feb 2024 11:04:52 +0100 Subject: [PATCH] Add special case for single-CNOT decomposition of controlled-U --- opensquirrel/cnot_decomposer.py | 39 ++++++++++------- opensquirrel/merger.py | 8 ++-- test/test_cnot_decomposer.py | 9 ++-- test/test_integration.py | 76 ++++++++++++++++++++------------- 4 files changed, 79 insertions(+), 53 deletions(-) diff --git a/opensquirrel/cnot_decomposer.py b/opensquirrel/cnot_decomposer.py index 75fd5907..65365290 100644 --- a/opensquirrel/cnot_decomposer.py +++ b/opensquirrel/cnot_decomposer.py @@ -1,7 +1,8 @@ import math +from opensquirrel import merger from opensquirrel.common import ATOL -from opensquirrel.default_gates import cnot, ry, rz +from opensquirrel.default_gates import cnot, ry, rz, x from opensquirrel.identity_filter import filter_out_identities from opensquirrel.replacer import Decomposer from opensquirrel.squirrel_ir import BlochSphereRotation, ControlledGate, Float, Gate @@ -29,30 +30,36 @@ def decompose(g: Gate) -> [Gate]: # ControlledGate's with 2+ control qubits are ignored. return [g] + target_qubit = g.target_gate.qubit + # Perform ZYZ decomposition on the target gate. # This gives us an ABC decomposition (U = AXBXC, ABC = I) of the target gate. # See https://threeplusone.com/pubs/on_gates.pdf - theta0, theta1, theta2 = get_zyz_decomposition_angles(g.target_gate.angle, g.target_gate.axis) - target_qubit = g.target_gate.qubit - # First try to see if we can get away with a single CNOT. - # FIXME: see https://github.com/QuTech-Delft/OpenSquirrel/issues/99 this could be extended, I believe. - if abs(abs(theta0 + theta2) % (2 * math.pi)) < ATOL and abs(abs(theta1 - math.pi) % (2 * math.pi)) < ATOL: - # g == rz(theta0) Y rz(theta2) == rz(theta0 - pi / 2) X rz(theta2 + pi / 2) - # theta0 + theta2 == 0 + # Try special case first, see https://arxiv.org/pdf/quant-ph/9503016.pdf lemma 5.5 + controlled_rotation_times_x = merger.compose_bloch_sphere_rotations(x(target_qubit), g.target_gate) + theta0_with_x, theta1_with_x, theta2_with_x = get_zyz_decomposition_angles( + controlled_rotation_times_x.angle, controlled_rotation_times_x.axis + ) + if abs((theta0_with_x - theta2_with_x) % (2 * math.pi)) < ATOL: + # The decomposition can use a single CNOT according to the lemma. + + A = [ry(q=target_qubit, theta=Float(-theta1_with_x / 2)), rz(q=target_qubit, theta=Float(-theta2_with_x))] - alpha0 = theta0 - math.pi / 2 - alpha2 = theta2 + math.pi / 2 + B = [ + rz(q=target_qubit, theta=Float(theta2_with_x)), + ry(q=target_qubit, theta=Float(theta1_with_x / 2)), + ] return filter_out_identities( - [ - rz(q=target_qubit, theta=Float(alpha2)), - cnot(control=g.control_qubit, target=target_qubit), - rz(q=target_qubit, theta=Float(alpha0)), - rz(q=g.control_qubit, theta=Float(g.target_gate.phase - math.pi / 2)), - ] + B + + [cnot(control=g.control_qubit, target=target_qubit)] + + A + + [rz(q=g.control_qubit, theta=Float(g.target_gate.phase - math.pi / 2))] ) + theta0, theta1, theta2 = get_zyz_decomposition_angles(g.target_gate.angle, g.target_gate.axis) + A = [ry(q=target_qubit, theta=Float(theta1 / 2)), rz(q=target_qubit, theta=Float(theta2))] B = [ diff --git a/opensquirrel/merger.py b/opensquirrel/merger.py index 17309904..24e2af6a 100644 --- a/opensquirrel/merger.py +++ b/opensquirrel/merger.py @@ -16,9 +16,11 @@ def compose_bloch_sphere_rotations(a: BlochSphereRotation, b: BlochSphereRotatio """ assert a.qubit == b.qubit, "Cannot merge two BlochSphereRotation's on different qubits" - combined_angle = 2 * acos( - cos(a.angle / 2) * cos(b.angle / 2) - sin(a.angle / 2) * sin(b.angle / 2) * np.dot(a.axis, b.axis) - ) + acos_argument = cos(a.angle / 2) * cos(b.angle / 2) - sin(a.angle / 2) * sin(b.angle / 2) * np.dot(a.axis, b.axis) + # This fixes float approximations like 1.0000000000002 which acos doesn't like. + acos_argument = max(min(acos_argument, 1.0), -1.0) + + combined_angle = 2 * acos(acos_argument) if abs(sin(combined_angle / 2)) < ATOL: return BlochSphereRotation.identity(a.qubit) diff --git a/test/test_cnot_decomposer.py b/test/test_cnot_decomposer.py index fdbc0103..8e47a3e8 100644 --- a/test/test_cnot_decomposer.py +++ b/test/test_cnot_decomposer.py @@ -29,13 +29,12 @@ def test_cnot(self): def test_cz(self): self.assertEqual( CNOTDecomposer.decompose(cz(Qubit(0), Qubit(1))), - # FIXME: this should only be H-CNOT-H no? Check https://github.com/QuTech-Delft/OpenSquirrel/issues/99 [ - rz(Qubit(1), Float(math.pi / 2)), + rz(Qubit(1), Float(math.pi)), + ry(Qubit(1), Float(math.pi / 2)), cnot(Qubit(0), Qubit(1)), - rz(Qubit(1), Float(-math.pi / 2)), - cnot(Qubit(0), Qubit(1)), - rz(Qubit(0), Float(math.pi / 2)), + ry(Qubit(1), Float(-math.pi / 2)), + rz(Qubit(1), Float(math.pi)), ], ) diff --git a/test/test_integration.py b/test/test_integration.py index fc75fc93..8d31f2b0 100644 --- a/test/test_integration.py +++ b/test/test_integration.py @@ -166,9 +166,6 @@ def test_libqasm_error(self): use_libqasm=True, ) - @unittest.skipIf( - importlib.util.find_spec("quantify_scheduler") is None, reason="quantify_scheduler is not installed" - ) def test_export_quantify_scheduler(self): myCircuit = Circuit.from_string( """ @@ -177,12 +174,16 @@ def test_export_quantify_scheduler(self): qubit[3] qreg h qreg[1] + cz qreg[0], qreg[1] + cnot qreg[0], qreg[1] crk qreg[0], qreg[1], 4 h qreg[0] """ ) myCircuit.decompose(decomposer=CNOTDecomposer) + + # Quantify-scheduler prefers CZ. myCircuit.replace( cnot, lambda control, target: [ @@ -191,34 +192,51 @@ def test_export_quantify_scheduler(self): h(target), ], ) - myCircuit.merge_single_qubit_gates() - myCircuit.decompose(decomposer=ZYZDecomposer) # FIXME: for best gate count we need a Z-XY decomposer. - - exported_schedule = myCircuit.export(format=ExportFormat.QUANTIFY_SCHEDULER) - - self.assertEqual(exported_schedule.name, "Exported OpenSquirrel circuit") - operation_ids = [v["operation_id"] for k, v in exported_schedule.schedulables.items()] - operations = [exported_schedule.operations[operation_id].name for operation_id in operation_ids] + # Diminish gate count by single-qubit gate fusion. + myCircuit.merge_single_qubit_gates() - self.assertEqual( - operations, - [ - "Rz(1.5707963, 'qreg[1]')", - "Rxy(0.19634954, 1.5707963, 'qreg[1]')", - "Rz(-1.5707963, 'qreg[1]')", - "CZ (qreg[0], qreg[1])", - "Rz(1.5707963, 'qreg[1]')", - "Rxy(-0.19634954, 1.5707963, 'qreg[1]')", - "Rz(-1.5707963, 'qreg[1]')", - "CZ (qreg[0], qreg[1])", - "Rz(0.19634954, 'qreg[0]')", - "Rxy(-1.5707963, 1.5707963, 'qreg[0]')", - "Rz(3.1415927, 'qreg[0]')", - "Rz(3.1415927, 'qreg[1]')", - "Rxy(1.5707963, 1.5707963, 'qreg[1]')", - ], - ) + # FIXME: for best gate count we need a Z-XY decomposer. + # See https://github.com/QuTech-Delft/OpenSquirrel/issues/98 + myCircuit.decompose(decomposer=ZYZDecomposer) + + if importlib.util.find_spec("quantify_scheduler") is None: + with self.assertRaisesRegex( + Exception, "quantify-scheduler is not installed, or cannot be installed on " "your system" + ): + myCircuit.export(format=ExportFormat.QUANTIFY_SCHEDULER) + else: + exported_schedule = myCircuit.export(format=ExportFormat.QUANTIFY_SCHEDULER) + + self.assertEqual(exported_schedule.name, "Exported OpenSquirrel circuit") + + operation_ids = [v["operation_id"] for k, v in exported_schedule.schedulables.items()] + operations = [exported_schedule.operations[operation_id].name for operation_id in operation_ids] + + self.assertEqual( + operations, + [ + "Rz(3.1415927, 'qreg[1]')", + "Rxy(1.5707963, 1.5707963, 'qreg[1]')", + "CZ (qreg[0], qreg[1])", + "Rz(3.1415927, 'qreg[1]')", + "Rxy(1.5707963, 1.5707963, 'qreg[1]')", + "CZ (qreg[0], qreg[1])", + "Rz(1.5707963, 'qreg[1]')", + "Rxy(0.19634954, 1.5707963, 'qreg[1]')", + "Rz(-1.5707963, 'qreg[1]')", + "CZ (qreg[0], qreg[1])", + "Rz(1.5707963, 'qreg[1]')", + "Rxy(-0.19634954, 1.5707963, 'qreg[1]')", + "Rz(-1.5707963, 'qreg[1]')", + "CZ (qreg[0], qreg[1])", + "Rz(0.19634954, 'qreg[0]')", + "Rxy(-1.5707963, 1.5707963, 'qreg[0]')", + "Rz(3.1415927, 'qreg[0]')", + "Rz(3.1415927, 'qreg[1]')", + "Rxy(1.5707963, 1.5707963, 'qreg[1]')", + ], + ) if __name__ == "__main__":