def optimize_circuit(self, circuit: circuits.Circuit):
# Tracks qubit phases (in half turns; multiply by pi to get radians).
qubit_phase = defaultdict(lambda: 0) # type: Dict[ops.QubitId, float]
def dump_tracked_phase(qubits: Iterable[ops.QubitId],
index: int) -> None:
"""Zeroes qubit_phase entries by emitting Z gates."""
for q in qubits:
p = qubit_phase[q]
if not decompositions.is_negligible_turn(p, self.tolerance):
dump_op = ops.Z(q)**(p * 2)
insertions.append((index, dump_op))
qubit_phase[q] = 0
deletions = [] # type: List[Tuple[int, ops.Operation]]
inline_intos = [] # type: List[Tuple[int, ops.Operation]]
insertions = [] # type: List[Tuple[int, ops.Operation]]
for moment_index, moment in enumerate(circuit):
for op in moment.operations:
# Move Z gates into tracked qubit phases.
h = _try_get_known_z_half_turns(op)
if h is not None:
q = op.qubits[0]
qubit_phase[q] += h / 2
deletions.append((moment_index, op))
continue
# Z gate before measurement is a no-op. Drop tracked phase.
if ops.MeasurementGate.is_measurement(op):
for q in op.qubits:
qubit_phase[q] = 0
# If there's no tracked phase, we can move on.
phases = [qubit_phase[q] for q in op.qubits]
if all(
decompositions.is_negligible_turn(p, self.tolerance)
for p in phases):
continue
# Try to move the tracked phasing over the operation.
phased_op = op
for i, p in enumerate(phases):
if not decompositions.is_negligible_turn(
p, self.tolerance):
phased_op = protocols.phase_by(phased_op,
-p,
i,
default=None)
if phased_op is not None:
deletions.append((moment_index, op))
inline_intos.append(
(moment_index, cast(ops.Operation, phased_op)))
else:
dump_tracked_phase(op.qubits, moment_index)
dump_tracked_phase(qubit_phase.keys(), len(circuit))
circuit.batch_remove(deletions)
circuit.batch_insert_into(inline_intos)
circuit.batch_insert(insertions)
def _potential_cross_whole_w(moment_index: int, op: ops.Operation,
tolerance: float, state: _OptimizerState) -> None:
"""Grabs or cancels a held W gate against an existing W gate.
[Where W(a) is shorthand for PhasedX(phase_exponent=a).]
Uses the following identity:
───W(a)───W(b)───
≡ ───Z^-a───X───Z^a───Z^-b───X───Z^b───
≡ ───Z^-a───Z^-a───Z^b───X───X───Z^b───
≡ ───Z^-a───Z^-a───Z^b───Z^b───
≡ ───Z^2(b-a)───
"""
state.deletions.append((moment_index, op))
_, phase_exponent = cast(Tuple[float, float],
_try_get_known_phased_pauli(op))
q = op.qubits[0]
a = state.held_w_phases.get(q)
b = phase_exponent
if a is None:
# Collect the gate.
state.held_w_phases[q] = b
else:
# Cancel the gate.
state.held_w_phases[q] = None
t = 2 * (b - a)
if not decompositions.is_negligible_turn(t / 2, tolerance):
leftover_phase = ops.Z(q)**t
state.inline_intos.append((moment_index, leftover_phase))
def dump_tracked_phase(qubits: Iterable[ops.Qid], index: int) -> None:
"""Zeroes qubit_phase entries by emitting Z gates."""
for q in qubits:
p = qubit_phase[q]
if not decompositions.is_negligible_turn(p, self.tolerance):
dump_op = ops.Z(q)**(p * 2)
insertions.append((index, dump_op))
qubit_phase[q] = 0
def optimize_circuit(self, circuit: circuits.Circuit):
state = _OptimizerState()
for moment_index, moment in enumerate(circuit):
for op in moment.operations:
affected = [q for q in op.qubits
if state.held_w_phases.get(q) is not None]
# Collect, phase, and merge Ws.
w = _try_get_known_phased_pauli(op)
if w is not None:
if decompositions.is_negligible_turn(
w[0] - 1,
self.tolerance):
_potential_cross_whole_w(moment_index,
op,
self.tolerance,
state)
else:
_potential_cross_partial_w(moment_index, op, state)
continue
if not affected:
continue
# Absorb Z rotations.
t = _try_get_known_z_half_turns(op)
if t is not None:
_absorb_z_into_w(moment_index, op, state)
continue
# Dump coherent flips into measurement bit flips.
if ops.op_gate_of_type(op, ops.MeasurementGate):
_dump_into_measurement(moment_index, op, state)
# Cross CZs using kickback.
if _try_get_known_cz_half_turns(op) is not None:
if len(affected) == 1:
_single_cross_over_cz(moment_index,
op,
affected[0],
state)
else:
_double_cross_over_cz(op, state)
continue
# Don't know how to handle this situation. Dump the gates.
_dump_held(op.qubits, moment_index, state)
# Put anything that's still held at the end of the circuit.
_dump_held(state.held_w_phases.keys(), len(circuit), state)
circuit.batch_remove(state.deletions)
circuit.batch_insert_into(state.inline_intos)
circuit.batch_insert(state.insertions)
def dump_tracked_phase(qubits: Iterable[ops.Qid], index: int) -> None:
"""Zeroes qubit_phase entries by emitting Z gates."""
for q in qubits:
p = qubit_phase[q]
qubit_phase[q] = 0
if decompositions.is_negligible_turn(p, self.tolerance):
continue
dumped = False
moment_index = circuit.prev_moment_operating_on([q], index)
if moment_index is not None:
op = circuit.moments[moment_index][q]
if op and isinstance(op.gate, ops.PhasedXZGate):
# Attach z-rotation to replacing PhasedXZ gate.
idx = phased_xz_replacements[moment_index, q]
_, _, repl_op = replacements[idx]
gate = cast(ops.PhasedXZGate, repl_op.gate)
repl_op = gate.with_z_exponent(p * 2).on(q)
replacements[idx] = (moment_index, op, repl_op)
dumped = True
if not dumped:
# Add a new Z gate
dump_op = ops.Z(q)**(p * 2)
insertions.append((index, dump_op))
def optimize_circuit(self, circuit: circuits.Circuit):
# Tracks qubit phases (in half turns; multiply by pi to get radians).
qubit_phase: Dict[ops.Qid, float] = defaultdict(lambda: 0)
deletions: List[Tuple[int, ops.Operation]] = []
replacements: List[Tuple[int, ops.Operation, ops.Operation]] = []
insertions: List[Tuple[int, ops.Operation]] = []
phased_xz_replacements: Dict[Tuple[int, ops.Qid], int] = {}
def dump_tracked_phase(qubits: Iterable[ops.Qid], index: int) -> None:
"""Zeroes qubit_phase entries by emitting Z gates."""
for q in qubits:
p = qubit_phase[q]
qubit_phase[q] = 0
if decompositions.is_negligible_turn(p, self.tolerance):
continue
dumped = False
moment_index = circuit.prev_moment_operating_on([q], index)
if moment_index is not None:
op = circuit.moments[moment_index][q]
if op and isinstance(op.gate, ops.PhasedXZGate):
# Attach z-rotation to replacing PhasedXZ gate.
idx = phased_xz_replacements[moment_index, q]
_, _, repl_op = replacements[idx]
gate = cast(ops.PhasedXZGate, repl_op.gate)
repl_op = gate.with_z_exponent(p * 2).on(q)
replacements[idx] = (moment_index, op, repl_op)
dumped = True
if not dumped:
# Add a new Z gate
dump_op = ops.Z(q)**(p * 2)
insertions.append((index, dump_op))
for moment_index, moment in enumerate(circuit):
for op in moment.operations:
# Move Z gates into tracked qubit phases.
h = _try_get_known_z_half_turns(op, self.eject_parameterized)
if h is not None:
q = op.qubits[0]
qubit_phase[q] += h / 2
deletions.append((moment_index, op))
continue
# Z gate before measurement is a no-op. Drop tracked phase.
if isinstance(op.gate, ops.MeasurementGate):
for q in op.qubits:
qubit_phase[q] = 0
# If there's no tracked phase, we can move on.
phases = [qubit_phase[q] for q in op.qubits]
if not isinstance(op.gate, ops.PhasedXZGate) and all(
decompositions.is_negligible_turn(p, self.tolerance)
for p in phases):
continue
if _is_swaplike(op):
a, b = op.qubits
qubit_phase[a], qubit_phase[b] = qubit_phase[
b], qubit_phase[a]
continue
# Try to move the tracked phasing over the operation.
phased_op = op
for i, p in enumerate(phases):
if not decompositions.is_negligible_turn(
p, self.tolerance):
phased_op = protocols.phase_by(phased_op,
-p,
i,
default=None)
if phased_op is not None:
gate = phased_op.gate
if isinstance(gate, ops.PhasedXZGate) and (
self.eject_parameterized or
not protocols.is_parameterized(gate.z_exponent)):
qubit = phased_op.qubits[0]
qubit_phase[qubit] += gate.z_exponent / 2
phased_op = gate.with_z_exponent(0).on(qubit)
repl_idx = len(replacements)
phased_xz_replacements[moment_index, qubit] = repl_idx
replacements.append((moment_index, op, phased_op))
else:
dump_tracked_phase(op.qubits, moment_index)
dump_tracked_phase(qubit_phase.keys(), len(circuit))
circuit.batch_remove(deletions)
circuit.batch_replace(replacements)
circuit.batch_insert(insertions)
