def as_late_as_possible(circuit: QuantumCircuit,
schedule_config: ScheduleConfig) -> Schedule:
"""
Return the pulse Schedule which implements the input circuit using an "as late as possible"
(alap) scheduling policy.
Circuit instructions are first each mapped to equivalent pulse
Schedules according to the command definition given by the schedule_config. Then, this circuit
instruction-equivalent Schedule is appended at the latest time that it can be without allowing
unnecessary time between instructions or allowing instructions with common qubits to overlap.
This method should improves the outcome fidelity over ASAP scheduling, because we may
maximize the time that the qubit remains in the ground state.
Args:
circuit: The quantum circuit to translate.
schedule_config: Backend specific parameters used for building the Schedule.
Returns:
A schedule corresponding to the input ``circuit`` with pulses occurring as late as
possible.
"""
qubit_time_available = defaultdict(int)
def update_times(inst_qubits: List[int], time: int = 0) -> None:
"""Update the time tracker for all inst_qubits to the given time."""
for q in inst_qubits:
qubit_time_available[q] = time
rev_stop_times = []
circ_pulse_defs = lower_gates(circuit, schedule_config)
for circ_pulse_def in reversed(circ_pulse_defs):
start_time = max(qubit_time_available[q]
for q in circ_pulse_def.qubits)
stop_time = start_time
if not isinstance(circ_pulse_def.schedule, Barrier):
stop_time += circ_pulse_def.schedule.duration
rev_stop_times.append(stop_time)
update_times(circ_pulse_def.qubits, stop_time)
last_stop = max(
t
for t in qubit_time_available.values()) if qubit_time_available else 0
start_times = [last_stop - t for t in reversed(rev_stop_times)]
timed_schedules = [(time, cpd.schedule)
for time, cpd in zip(start_times, circ_pulse_defs)
if not isinstance(cpd.schedule, Barrier)]
schedule = Schedule.initialize_from(circuit)
for time, inst in timed_schedules:
schedule.insert(time, inst, inplace=True)
return schedule
def as_soon_as_possible(circuit: QuantumCircuit,
schedule_config: ScheduleConfig) -> Schedule:
"""
Return the pulse Schedule which implements the input circuit using an "as soon as possible"
(asap) scheduling policy.
Circuit instructions are first each mapped to equivalent pulse
Schedules according to the command definition given by the schedule_config. Then, this circuit
instruction-equivalent Schedule is appended at the earliest time at which all qubits involved
in the instruction are available.
Args:
circuit: The quantum circuit to translate.
schedule_config: Backend specific parameters used for building the Schedule.
Returns:
A schedule corresponding to the input ``circuit`` with pulses occurring as early as
possible.
"""
qubit_time_available = defaultdict(int)
def update_times(inst_qubits: List[int], time: int = 0) -> None:
"""Update the time tracker for all inst_qubits to the given time."""
for q in inst_qubits:
qubit_time_available[q] = time
start_times = []
circ_pulse_defs = lower_gates(circuit, schedule_config)
for circ_pulse_def in circ_pulse_defs:
start_time = max(qubit_time_available[q]
for q in circ_pulse_def.qubits)
stop_time = start_time
if not isinstance(circ_pulse_def.schedule, Barrier):
stop_time += circ_pulse_def.schedule.duration
start_times.append(start_time)
update_times(circ_pulse_def.qubits, stop_time)
timed_schedules = [(time, cpd.schedule)
for time, cpd in zip(start_times, circ_pulse_defs)
if not isinstance(cpd.schedule, Barrier)]
schedule = Schedule.initialize_from(circuit)
for time, inst in timed_schedules:
schedule.insert(time, inst, inplace=True)
return schedule
def sequence(scheduled_circuit: QuantumCircuit,
schedule_config: ScheduleConfig) -> Schedule:
"""
Return the pulse Schedule which implements the input scheduled circuit.
Assume all measurements are done at once at the last of the circuit.
Schedules according to the command definition given by the schedule_config.
Args:
scheduled_circuit: The scheduled quantum circuit to translate.
schedule_config: Backend specific parameters used for building the Schedule.
Returns:
A schedule corresponding to the input ``circuit``.
Raises:
QiskitError: If invalid scheduled circuit is supplied.
"""
circ_pulse_defs = lower_gates(scheduled_circuit, schedule_config)
# find the measurement start time (assume measurement once)
def _meas_start_time():
_qubit_time_available = defaultdict(int)
for inst, qubits, _ in scheduled_circuit.data:
if isinstance(inst, Measure):
return _qubit_time_available[qubits[0]]
for q in qubits:
_qubit_time_available[q] += inst.duration
return None
meas_time = _meas_start_time()
# restore start times
qubit_time_available = {}
start_times = []
out_circ_pulse_defs = []
for circ_pulse_def in circ_pulse_defs:
active_qubits = [
q for q in circ_pulse_def.qubits if q in qubit_time_available
]
start_time = max((qubit_time_available[q] for q in active_qubits),
default=0)
for q in active_qubits:
if qubit_time_available[q] != start_time:
# print(q, ":", qubit_time_available[q], "!=", start_time)
raise QiskitError("Invalid scheduled circuit.")
stop_time = start_time
if not isinstance(circ_pulse_def.schedule, Barrier):
stop_time += circ_pulse_def.schedule.duration
delay_overlaps_meas = False
for q in circ_pulse_def.qubits:
qubit_time_available[q] = stop_time
if (meas_time is not None
and circ_pulse_def.schedule.name == "delay"
and stop_time > meas_time):
qubit_time_available[q] = meas_time
delay_overlaps_meas = True
# skip to delays overlapping measures and barriers
if not delay_overlaps_meas and not isinstance(circ_pulse_def.schedule,
Barrier):
start_times.append(start_time)
out_circ_pulse_defs.append(circ_pulse_def)
timed_schedules = [(time, cpd.schedule)
for time, cpd in zip(start_times, out_circ_pulse_defs)]
sched = Schedule(*timed_schedules, name=scheduled_circuit.name)
return pad(sched)