# This code is part of Qiskit.
#
# (C) Copyright IBM 2020.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.
""" CircuitSampler Class """
from typing import Optional, Dict, List, Union, cast, Any, Tuple
import logging
from functools import partial
from time import time
from qiskit.providers import BaseBackend
from qiskit.providers import Backend
from qiskit.circuit import QuantumCircuit, Parameter, ParameterExpression
from qiskit import QiskitError
from qiskit.aqua import QuantumInstance, AquaError
from qiskit.aqua.utils.backend_utils import is_aer_provider, is_statevector_backend
from qiskit.aqua.operators.operator_base import OperatorBase
from qiskit.aqua.operators.list_ops.list_op import ListOp
from qiskit.aqua.operators.state_fns.state_fn import StateFn
from qiskit.aqua.operators.state_fns.circuit_state_fn import CircuitStateFn
from qiskit.aqua.operators.state_fns.dict_state_fn import DictStateFn
from qiskit.aqua.operators.converters.converter_base import ConverterBase
logger = logging.getLogger(__name__)
[docs]class CircuitSampler(ConverterBase):
"""
The CircuitSampler traverses an Operator and converts any CircuitStateFns into
approximations of the state function by a DictStateFn or VectorStateFn using a quantum
backend. Note that in order to approximate the value of the CircuitStateFn, it must 1) send
state function through a depolarizing channel, which will destroy all phase information and
2) replace the sampled frequencies with **square roots** of the frequency, rather than the raw
probability of sampling (which would be the equivalent of sampling the **square** of the
state function, per the Born rule.
The CircuitSampler aggressively caches transpiled circuits to handle re-parameterization of
the same circuit efficiently. If you are converting multiple different Operators,
you are better off using a different CircuitSampler for each Operator to avoid cache thrashing.
"""
[docs] def __init__(self,
backend: Union[Backend, BaseBackend, QuantumInstance],
statevector: Optional[bool] = None,
param_qobj: bool = False,
attach_results: bool = False) -> None:
"""
Args:
backend: The quantum backend or QuantumInstance to use to sample the circuits.
statevector: If backend is a statevector backend, whether to replace the
CircuitStateFns with DictStateFns (from the counts) or VectorStateFns (from the
statevector). ``None`` will set this argument automatically based on the backend.
attach_results: Whether to attach the data from the backend ``Results`` object for
a given ``CircuitStateFn``` to an ``execution_results`` field added the converted
``DictStateFn`` or ``VectorStateFn``.
param_qobj: Whether to use Aer's parameterized Qobj capability to avoid re-assembling
the circuits.
Raises:
ValueError: Set statevector or param_qobj True when not supported by backend.
"""
self._quantum_instance = backend if isinstance(backend, QuantumInstance) else\
QuantumInstance(backend=backend)
self._statevector = statevector if statevector is not None \
else self.quantum_instance.is_statevector
self._param_qobj = param_qobj
self._attach_results = attach_results
self._check_quantum_instance_and_modes_consistent()
# Object state variables
self._last_op = None
self._reduced_op_cache = None
self._circuit_ops_cache = {} # type: Dict[int, CircuitStateFn]
self._transpiled_circ_cache = None # type: Optional[List[Any]]
self._transpiled_circ_templates = None # type: Optional[List[Any]]
self._transpile_before_bind = True
self._binding_mappings = None
def _check_quantum_instance_and_modes_consistent(self) -> None:
""" Checks whether the statevector and param_qobj settings are compatible with the
backend
Raises:
ValueError: statevector or param_qobj are True when not supported by backend.
"""
if self._statevector and not is_statevector_backend(self.quantum_instance.backend):
raise ValueError('Statevector mode for circuit sampling requires statevector '
'backend, not {}.'.format(self.quantum_instance.backend))
if self._param_qobj and not is_aer_provider(self.quantum_instance.backend):
raise ValueError('Parameterized Qobj mode requires Aer '
'backend, not {}.'.format(self.quantum_instance.backend))
@property
def backend(self) -> Union[Backend, BaseBackend]:
""" Returns the backend.
Returns:
The backend used by the CircuitSampler
"""
return self.quantum_instance.backend
@backend.setter
def backend(self, backend: Union[Backend, BaseBackend]):
""" Sets backend without additional configuration. """
self.set_backend(backend)
[docs] def set_backend(self, backend: Union[Backend, BaseBackend], **kwargs) -> None:
""" Sets backend with configuration.
Raises:
ValueError: statevector or param_qobj are True when not supported by backend.
"""
self.quantum_instance = QuantumInstance(backend)
self.quantum_instance.set_config(**kwargs)
@property
def quantum_instance(self) -> QuantumInstance:
""" Returns the quantum instance.
Returns:
The QuantumInstance used by the CircuitSampler
"""
return self._quantum_instance
@quantum_instance.setter
def quantum_instance(self, quantum_instance: Union[QuantumInstance,
Backend, BaseBackend]) -> None:
""" Sets the QuantumInstance.
Raises:
ValueError: statevector or param_qobj are True when not supported by backend.
"""
if isinstance(quantum_instance, (Backend, BaseBackend)):
quantum_instance = QuantumInstance(quantum_instance)
self._quantum_instance = quantum_instance
self._check_quantum_instance_and_modes_consistent()
# pylint: disable=arguments-differ
[docs] def convert(self,
operator: OperatorBase,
params: Optional[Dict[Parameter,
Union[float, List[float], List[List[float]]]]] = None
) -> OperatorBase:
r"""
Converts the Operator to one in which the CircuitStateFns are replaced by
DictStateFns or VectorStateFns. Extracts the CircuitStateFns out of the Operator,
caches them, calls ``sample_circuits`` below to get their converted replacements,
and replaces the CircuitStateFns in operator with the replacement StateFns.
Args:
operator: The Operator to convert
params: A dictionary mapping parameters to either single binding values or lists of
binding values.
Returns:
The converted Operator with CircuitStateFns replaced by DictStateFns or VectorStateFns.
Raises:
AquaError: if extracted circuits are empty.
"""
if self._last_op is None or id(operator) != id(self._last_op):
# Clear caches
self._last_op = operator
self._reduced_op_cache = None
self._circuit_ops_cache = None
self._transpiled_circ_cache = None
self._transpile_before_bind = True
if not self._reduced_op_cache:
operator_dicts_replaced = operator.to_circuit_op()
self._reduced_op_cache = operator_dicts_replaced.reduce()
if not self._circuit_ops_cache:
self._circuit_ops_cache = {}
self._extract_circuitstatefns(self._reduced_op_cache)
if not self._circuit_ops_cache:
raise AquaError(
'Circuits are empty. '
'Check that the operator is an instance of CircuitStateFn or its ListOp.'
)
if params:
p_0 = list(params.values())[0] # type: ignore
num_parameterizations = len(cast(List, p_0))
param_bindings = [{param: value_list[i] # type: ignore
for (param, value_list) in params.items()}
for i in range(num_parameterizations)]
else:
param_bindings = None
num_parameterizations = 1
# Don't pass circuits if we have in the cache, the sampling function knows to use the cache
circs = list(self._circuit_ops_cache.values()) if not self._transpiled_circ_cache else None
p_b = cast(List[Dict[Parameter, List[float]]], param_bindings)
sampled_statefn_dicts = self.sample_circuits(circuit_sfns=circs,
param_bindings=p_b)
def replace_circuits_with_dicts(operator, param_index=0):
if isinstance(operator, CircuitStateFn):
return sampled_statefn_dicts[id(operator)][param_index]
elif isinstance(operator, ListOp):
return operator.traverse(partial(replace_circuits_with_dicts,
param_index=param_index))
else:
return operator
if params:
return ListOp([replace_circuits_with_dicts(self._reduced_op_cache, param_index=i)
for i in range(num_parameterizations)])
else:
return replace_circuits_with_dicts(self._reduced_op_cache, param_index=0)
def _extract_circuitstatefns(self, operator: OperatorBase) -> None:
r"""
Recursively extract the ``CircuitStateFns`` contained in operator into the
``_circuit_ops_cache`` field.
"""
if isinstance(operator, CircuitStateFn):
self._circuit_ops_cache[id(operator)] = operator
elif isinstance(operator, ListOp):
for op in operator.oplist:
self._extract_circuitstatefns(op)
[docs] def sample_circuits(self,
circuit_sfns: Optional[List[CircuitStateFn]] = None,
param_bindings: Optional[List[Dict[Parameter, List[float]]]] = None
) -> Dict[int, Union[StateFn, List[StateFn]]]:
r"""
Samples the CircuitStateFns and returns a dict associating their ``id()`` values to their
replacement DictStateFn or VectorStateFn. If param_bindings is provided,
the CircuitStateFns are broken into their parameterizations, and a list of StateFns is
returned in the dict for each circuit ``id()``. Note that param_bindings is provided here
in a different format than in ``convert``, and lists of parameters within the dict is not
supported, and only binding dicts which are valid to be passed into Terra can be included
in this list.
Args:
circuit_sfns: The list of CircuitStateFns to sample.
param_bindings: The parameterizations to bind to each CircuitStateFn.
Returns:
The dictionary mapping ids of the CircuitStateFns to their replacement StateFns.
Raises:
AquaError: if extracted circuits are empty.
"""
if not circuit_sfns and not self._transpiled_circ_cache:
raise AquaError('CircuitStateFn is empty and there is no cache.')
if circuit_sfns:
if self._statevector:
circuits = [op_c.to_circuit(meas=False) for op_c in circuit_sfns]
else:
circuits = [op_c.to_circuit(meas=True) for op_c in circuit_sfns]
try:
self._transpiled_circ_cache = self.quantum_instance.transpile(circuits)
except QiskitError:
logger.debug(r'CircuitSampler failed to transpile circuits with unbound '
r'parameters. Attempting to transpile only when circuits are bound '
r'now, but this can hurt performance due to repeated transpilation.')
self._transpile_before_bind = False
self._transpiled_circ_cache = circuits
else:
circuit_sfns = list(self._circuit_ops_cache.values())
if param_bindings is not None:
if self._param_qobj:
start_time = time()
ready_circs = self._prepare_parameterized_run_config(param_bindings)
end_time = time()
logger.debug('Parameter conversion %.5f (ms)', (end_time - start_time) * 1000)
else:
start_time = time()
ready_circs = [circ.assign_parameters(binding)
for circ in self._transpiled_circ_cache
for binding in param_bindings]
end_time = time()
logger.debug('Parameter binding %.5f (ms)', (end_time - start_time) * 1000)
else:
ready_circs = self._transpiled_circ_cache
results = self.quantum_instance.execute(ready_circs,
had_transpiled=self._transpile_before_bind)
if param_bindings is not None and self._param_qobj:
self._clean_parameterized_run_config()
# Wipe parameterizations, if any
# self.quantum_instance._run_config.parameterizations = None
sampled_statefn_dicts = {}
for i, op_c in enumerate(circuit_sfns):
# Taking square root because we're replacing a statevector
# representation of probabilities.
reps = len(param_bindings) if param_bindings is not None else 1
c_statefns = []
for j in range(reps):
circ_index = (i * reps) + j
circ_results = results.data(circ_index)
if 'expval_measurement' in circ_results.get('snapshots', {}).get(
'expectation_value', {}):
snapshot_data = results.data(circ_index)['snapshots']
avg = snapshot_data['expectation_value']['expval_measurement'][0]['value']
if isinstance(avg, (list, tuple)):
# Aer versions before 0.4 use a list snapshot format
# which must be converted to a complex value.
avg = avg[0] + 1j * avg[1]
# Will be replaced with just avg when eval is called later
num_qubits = circuit_sfns[0].num_qubits
result_sfn = DictStateFn('0' * num_qubits,
is_measurement=op_c.is_measurement) * avg
elif self._statevector:
result_sfn = StateFn(op_c.coeff * results.get_statevector(circ_index),
is_measurement=op_c.is_measurement)
else:
shots = self.quantum_instance._run_config.shots
result_sfn = StateFn({b: (v / shots) ** 0.5 * op_c.coeff
for (b, v) in results.get_counts(circ_index).items()},
is_measurement=op_c.is_measurement)
if self._attach_results:
result_sfn.execution_results = circ_results
c_statefns.append(result_sfn)
sampled_statefn_dicts[id(op_c)] = c_statefns
return sampled_statefn_dicts
def _build_aer_params(self,
circuit: QuantumCircuit,
building_param_tables: Dict[Tuple[int, int], List[float]],
input_params: Dict[Parameter, List[float]]
) -> None:
def resolve_param(inst_param):
if not isinstance(inst_param, ParameterExpression):
return None
param_mappings = {}
for param in inst_param._parameter_symbols.keys():
if param not in input_params:
raise ValueError('unexpected parameter: {0}'.format(param))
param_mappings[param] = input_params[param]
return float(inst_param.bind(param_mappings))
gate_index = 0
for inst, _, _ in circuit.data:
param_index = 0
for inst_param in inst.params:
val = resolve_param(inst_param)
if val is not None:
param_key = (gate_index, param_index)
if param_key in building_param_tables:
building_param_tables[param_key].append(val)
else:
building_param_tables[param_key] = [val]
param_index += 1
gate_index += 1
def _prepare_parameterized_run_config(self, param_bindings:
List[Dict[Parameter, List[float]]]) -> List[Any]:
self.quantum_instance._run_config.parameterizations = []
if self._transpiled_circ_templates is None \
or len(self._transpiled_circ_templates) != len(self._transpiled_circ_cache):
# temporally resolve parameters of self._transpiled_circ_cache
# They will be overridden in Aer from the next iterations
self._transpiled_circ_templates = [circ.assign_parameters(param_bindings[0])
for circ in self._transpiled_circ_cache]
for circ in self._transpiled_circ_cache:
building_param_tables = {} # type: Dict[Tuple[int, int], List[float]]
for param_binding in param_bindings:
self._build_aer_params(circ, building_param_tables, param_binding)
param_tables = []
for gate_and_param_indices in building_param_tables:
gate_index = gate_and_param_indices[0]
param_index = gate_and_param_indices[1]
param_tables.append([
[gate_index, param_index], building_param_tables[(gate_index, param_index)]])
self.quantum_instance._run_config.parameterizations.append(param_tables)
return self._transpiled_circ_templates
def _clean_parameterized_run_config(self) -> None:
self.quantum_instance._run_config.parameterizations = []