Source code for pennylane_qiskit.converter
# Copyright 2019 Xanadu Quantum Technologies Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
r"""
This module contains functions for converting Qiskit QuantumCircuit objects
into PennyLane circuit templates.
"""
from typing import Dict, Any, Iterable, Sequence, Union
import warnings
from functools import partial, reduce
import numpy as np
from qiskit import QuantumCircuit
from qiskit.circuit import Parameter, ParameterExpression, ParameterVector
from qiskit.circuit import Measure, Barrier, ControlFlowOp, Clbit
from qiskit.circuit.classical import expr
from qiskit.circuit.controlflow.switch_case import _DefaultCaseType
from qiskit.circuit.library import GlobalPhaseGate
from qiskit.circuit.parametervector import ParameterVectorElement
from qiskit.exceptions import QiskitError
from qiskit.quantum_info import SparsePauliOp
from sympy import lambdify
import pennylane as qml
import pennylane.ops as pennylane_ops
from pennylane_qiskit.qiskit_device import QISKIT_OPERATION_MAP
# pylint: disable=too-many-instance-attributes
inv_map = {v.__name__: k for k, v in QISKIT_OPERATION_MAP.items()}
dagger_map = {
"SdgGate": qml.S,
"TdgGate": qml.T,
"SXdgGate": qml.SX,
"GlobalPhaseGate": qml.GlobalPhase,
}
referral_to_forum = (
"\n \nIf you are experiencing any difficulties with converting circuits from Qiskit, you can reach out "
"\non the PennyLane forum at https://discuss.pennylane.ai/c/pennylane-plugins/pennylane-qiskit/"
)
def _check_parameter_bound(
param: Parameter,
unbound_params: Dict[Union[Parameter, ParameterVector], Any],
):
"""Utility function determining if a certain parameter in a QuantumCircuit has
been bound.
Args:
param (qiskit.circuit.Parameter): the parameter to be checked
unbound_params (dict[qiskit.circuit.Parameter | qiskit.circuit.ParameterVector, Any]):
a dictionary mapping qiskit parameters (or vectors) to trainable parameter values
"""
if isinstance(param, ParameterVectorElement):
if param.vector not in unbound_params:
raise ValueError(f"The vector of parameter {param} was not bound correctly.")
elif isinstance(param, Parameter):
if param not in unbound_params:
raise ValueError(f"The parameter {param} was not bound correctly.")
def _process_basic_param_args(params, *args, **kwargs):
"""Process the basic conditions for parameter dictionary computation.
Returns:
params (dict): A dictionary mapping ``quantum_circuit.parameters`` to values
flag (bool): Indicating whether the returned ``params`` can be used.
"""
# if no kwargs are passed, and a dictionary has been passed as a single argument, then assume it is params
if params is None and not kwargs and (len(args) == 1 and isinstance(args[0], dict)):
return (args[0], True)
if not args and not kwargs:
return (params, True)
# make params dict if using args and/or kwargs
if params is not None:
raise RuntimeError(
"Cannot define parameters via the params kwarg when passing Parameter values "
"as individual args or kwargs."
)
return ({}, False)
def _expected_parameters(quantum_circuit):
"""Gets the expected parameters and a string of their names from the QuantumCircuit.
Primarily serves to change a list of Parameters and ParameterVectorElements into a list
of Parameters and ParameterVectors. I.e.:
[Parameter('a'), ParameterVectorElement('v[0]'), ParameterVectorElement('v[1]'), ParameterVectorElement('v[2]')]
becomes [Parameter('a'), ParameterVector(name='v', length=3)].
Returns:
expected_params: The reorganized list of Parameters, containing Parameter and ParameterVector
param_name_string: a string listing the parameter names, i.e. in the example above, 'a, v'
"""
expected_params = {}
for p in quantum_circuit.parameters:
# we want the p.vector if p is a ParameterVectorElement, otherwise p
param = getattr(p, "vector", p)
expected_params.update({param.name: param})
param_name_string = ", ".join(expected_params.keys())
return expected_params, param_name_string
def _format_params_dict(quantum_circuit, params, *args, **kwargs):
"""Processes the inputs for calling the quantum function and returns
a dictionary of the format ``{Parameter("name"): value}`` for all the parameters.
For a ``quantum_circuit`` with parameters ``[Parameter("phi"), Parameter("psi"), Parameter("theta")]``,
inputs can be one of the following:
1. the kwargs passed to when calling the qfunc, other than ``params`` and ``wires``.
The keys in kwargs are expected to correspond to the names of the Parameters on
the QuantumCircuit, i.e. ``(qc, None, phi=0.35, theta=0.2, psi=1.7)``
2. the args passed when calling the qfunc, i.e. ``(qc, None, 0.35, 1.7, 0.2)``. These
are assigned to the Parameters as the are ordered on the Qiskit QuantumCircuit:
alphabetized by Parameter name
3. Some combination of args and kwargs, i.e. ``(qc, None, 0.35, 0.2, psi=1.7)``
4. (legacy) ``params`` from the kwarg ``params`` of the qfunc call, which is expected
to already be a dictionary of the format ``{Parameter("name"): value}``, i.e.
``(qc, {Parameter("phi"): 0.35, Parameter("psi"): 1.7, Parameter("theta"): 0.2})``
5. (legacy) ``params`` passed as a single arg, which is expected
to already be a dictionary of the format ``{Parameter("name"): value}``, i.e.
``(qc, None, {Parameter("phi"): 0.35, Parameter("psi"): 1.7, Parameter("theta"): 0.2})``
Returns:
params (dict): A dictionary mapping ``quantum_circuit.parameters`` to values
"""
params, flag = _process_basic_param_args(params, *args, **kwargs)
if flag:
return params
expected_params, param_name_string = _expected_parameters(quantum_circuit)
# populate it with any parameters defined as kwargs
for k, v in kwargs.items():
# the key needs to be the actual Parameter, whereas kwargs keys are parameter names
if not k in expected_params:
raise TypeError(
f"Got unexpected parameter keyword argument '{k}'. Circuit contains parameters: {param_name_string} {referral_to_forum}"
)
params[expected_params[k]] = v
# get any parameters not defined in kwargs (may be all of them) and match to args in order
expected_arg_params = [param for name, param in expected_params.items() if name not in kwargs]
has_param_vectors = np.any([isinstance(p, ParameterVector) for p in expected_arg_params])
# if too many args were passed to the function call, raise an error
# all other checks regarding correct arguments will be processed in _check_circuit_and_assign_parameters
# (based on the full params dict generated by this function), but this information can only be captured here
if len(args) > len(expected_arg_params):
param_vector_info = (
"Note that PennyLane expects to recieve a ParameterVector as a single argument "
"containing all ParameterVectorElements."
if has_param_vectors
else ""
)
raise TypeError(
f"Expected {len(expected_arg_params)} positional argument{'s' if len(expected_arg_params) > 1 else ''} but {len(args)} were given. {param_vector_info} {referral_to_forum}"
)
params.update(dict(zip(expected_arg_params, args)))
return params
def _extract_variable_refs(params: Dict[Parameter, Any]) -> Dict[Parameter, Any]:
"""Iterate through the parameter mapping to be bound to the circuit,
and return a dictionary containing the trainable parameters.
Args:
params (dict): dictionary of the parameters in the circuit to their corresponding values
Returns:
dict[qiskit.circuit.Parameter, Any]: a dictionary mapping
qiskit parameters to trainable parameter values
"""
variable_refs = {}
# map qiskit parameters to PennyLane trainable parameter values
if params is not None:
for k, v in params.items():
if qml.math.requires_grad(v):
# Values can be arrays of size 1, need to extract the Python scalar
# (this can happen e.g. when indexing into a PennyLane numpy array)
if isinstance(v, np.ndarray) and v.size == 1:
v = v.item()
variable_refs[k] = v
return variable_refs # map qiskit parameters to trainable parameter values
def _check_circuit_and_assign_parameters(
quantum_circuit: QuantumCircuit, params: dict, diff_params: dict
) -> QuantumCircuit:
"""Utility function for checking for a valid quantum circuit and then assigning the parameters.
Args:
quantum_circuit (QuantumCircuit): the quantum circuit to check and bind the parameters for
params (dict): dictionary of the parameters in the circuit to their corresponding values
diff_params (dict): dictionary mapping the differentiable parameters to trainable parameter
values
Returns:
QuantumCircuit: quantum circuit with bound parameters
"""
if not isinstance(quantum_circuit, QuantumCircuit):
raise ValueError(f"The circuit {quantum_circuit} is not a valid Qiskit QuantumCircuit.")
# confirm parameter names are valid for conversion to PennyLane
for name in ["wires", "params"]:
if name in [p.name for p in quantum_circuit.parameters]:
raise RuntimeError(
f"Cannot interpret QuantumCircuit with parameter '{name}' as a PennyLane "
f"quantum function, as this argument is reserved. {referral_to_forum}"
)
expected_params, param_name_string = _expected_parameters(quantum_circuit)
if params is None:
if quantum_circuit.parameters:
s = "s" if len(quantum_circuit.parameters) > 1 else ""
raise TypeError(
f"Missing required argument{s} to define Parameter value{s} for: {param_name_string} {referral_to_forum}"
)
return quantum_circuit
# if any parameters are missing a value, raise an error
undefined_params = [name for name, param in expected_params.items() if param not in params]
if undefined_params:
s = "s" if len(undefined_params) > 1 else ""
param_names = ", ".join(undefined_params)
raise TypeError(
f"Missing {len(undefined_params)} required argument{s} to define Parameter value{s} for: {param_names}. {referral_to_forum}"
)
for k in diff_params:
# Since we don't bind trainable values to Qiskit circuits,
# we must remove them from the binding dictionary before binding.
del params[k]
# Disabling "strict" assignment allows extra parameters to be ignored.
return quantum_circuit.assign_parameters(params, strict=False)
def _get_operation_params(instruction, unbound_params) -> list:
"""Extract the bound parameters from the operation.
If the bound parameters are a Qiskit ParameterExpression, then replace it with
the corresponding PennyLane variable from the unbound_params dictionary.
Args:
instruction (qiskit.circuit.Instruction): a qiskit's quantum circuit instruction
unbound_params dict[qiskit.circuit.Parameter, Any]: a dictionary mapping
qiskit parameters to trainable parameter values
Returns:
list: bound parameters of the given instruction
"""
operation_params = []
for p in instruction.params:
_check_parameter_bound(p, unbound_params)
if isinstance(p, ParameterExpression):
if p.parameters: # non-empty set = has unbound parameters
f_args = []
f_params = []
# Ensure duplicate subparameters are only appended once.
f_param_names = set()
for subparam in p.parameters:
if isinstance(subparam, ParameterVectorElement):
# Unfortunately, parameter vector elements are named using square brackets.
# As a result, element names are not a valid Python identifier which causes
# issues with SymPy. To get around this, we create a temporary parameter
# representing the entire vector and pass that into the SymPy function.
parameter = Parameter(subparam.vector.name)
argument = unbound_params.get(subparam.vector)
else:
parameter = subparam
argument = unbound_params.get(subparam)
if parameter.name not in f_param_names:
f_param_names.add(parameter.name)
f_params.append(parameter)
f_args.append(argument)
f_expr = getattr(p, "_symbol_expr")
f = lambdify(f_params, f_expr, modules=qml.numpy)
operation_params.append(f(*f_args))
else: # needed for qiskit<0.43.1
operation_params.append(float(p)) # pragma: no cover
else:
operation_params.append(p)
return operation_params
def map_wires(qc_wires: list, wires: list) -> dict:
"""Utility function mapping the wires specified in a quantum circuit with the wires
specified by the user for the template.
Args:
qc_wires (list): wires from the converted quantum circuit
wires (list): wires specified for the template
Returns:
dict[int, int]: map from quantum circuit wires to the user defined wires
"""
if wires is None:
return dict(zip(qc_wires, range(len(qc_wires))))
if len(qc_wires) == len(wires):
return dict(zip(qc_wires, wires))
raise qml.QuantumFunctionError(
f"The specified number of wires - {len(wires)} - does not match "
"the number of wires the loaded quantum circuit acts on."
)
# pylint:disable=too-many-statements, too-many-branches
[docs]
def load(quantum_circuit: QuantumCircuit, measurements=None):
"""Loads a PennyLane template from a Qiskit QuantumCircuit.
Warnings are created for each of the QuantumCircuit instructions that were
not incorporated in the PennyLane template.
Args:
quantum_circuit (qiskit.QuantumCircuit): the QuantumCircuit to be converted
measurements (None | pennylane.measurements.MeasurementProcess | list[pennylane.measurements.MeasurementProcess]):
the PennyLane `measurements <https://docs.pennylane.ai/en/stable/introduction/measurements.html>`_
that override the terminal measurements that may be present in the input circuit
Returns:
function: The resulting PennyLane template.
"""
# pylint:disable=too-many-branches, fixme, protected-access
def _function(*args, params: dict = None, wires: list = None, **kwargs):
"""Returns a PennyLane quantum function created based on the input QuantumCircuit.
Warnings are created for each of the QuantumCircuit instructions that were
not incorporated in the PennyLane template.
If the QuantumCircuit contains unbound parameters, this function must be passed
parameter values. These can be passed as positional arguments (provided in the same
order that they are stored on the QuantumCircuit used to generate this function),
keyword arguments with keywords matching the parameter names, or as a single dictionary
with the parameters (not parameter names) as keys.
Args:
*args: positional arguments defining the value of the parameters that need to be assigned
in the QuantumCircuit
Kwargs:
**kwargs: keyword arguments matching the names of the parameters beind defined
params (dict): a dictionary with Parameter keys, specifying the parameters that need
to be bound in the QuantumCircuit
wires (Sequence[int] or int): The wires the converted template acts on.
Note that if the original QuantumCircuit acted on :math:`N` qubits,
then this must be a list of length :math:`N`.
Returns:
function: the new PennyLane template
.. warning::
Because this function takes ``params`` and ``wires`` as arguments in addition to taking
any args and kwargs to set parameter values, the ``params`` and ``wires`` arguments are
reserved, and cannot be parameter names in the QuantumCircuit.
**Example**
This function was created by doing something like:
.. code-block:: python
from qiskit.circuit import Parameter, QuantumCircuit
import pennylane as qml
a = Parameter("alpha")
b = Parameter("beta")
c = Parameter("gamma")
qc = QuantumCircuit(2, 2)
qc.rx(a, 0)
qc.rx(b * c, 1)
this_function = qml.from_qiskit(qc, measurements=[qml.PauliZ(0), qml.PauliZ(1)])
For the circuit above, based on ``Parameters`` with names 'alpha', 'beta' and 'gamma', all of the following are
valid inputs to set the Parameter values for this template:
.. code-block:: python
# positional arguments passed in alphabetical order (alpha, beta, gamma)
circuit = this_function(np.pi, 0.5, np.pi)
# kwargs are parameter names
circuit = this_function(alpha=np.pi, beta=0.5, gamma=np.pi)
# kwargs and args can be combined
circuit = this_function(np.pi, np.pi, beta=0.5)
# a dictionary - note that keys are not the names, but the Parameters themselves
circuit = this_function(params={a: np.pi, b: 0.5, c: np.pi})
"""
# organize parameters, format trainable parameter values correctly,
# and then bind the parameters to the circuit
params = _format_params_dict(quantum_circuit, params, *args, **kwargs)
unbound_params = _extract_variable_refs(params)
qc = _check_circuit_and_assign_parameters(quantum_circuit, params, unbound_params)
# Wires from a qiskit circuit have unique IDs, so their hashes are unique too
qc_wires = [hash(q) for q in qc.qubits]
wire_map = map_wires(qc_wires, wires)
# Stores the measurements encountered in the circuit
# terminal_meas / mid_circ_meas -> terminal / mid-circuit measurements
# mid_circ_regs -> maps the classical registers to the measurements done
terminal_meas, mid_circ_meas = [], []
mid_circ_regs = {}
# Processing the dictionary of parameters passed
for idx, circuit_instruction in enumerate(qc.data):
(instruction, qargs, cargs) = circuit_instruction
# the new Singleton classes have different names than the objects they represent,
# but base_class.__name__ still matches
instruction_name = getattr(instruction, "base_class", instruction.__class__).__name__
# New Qiskit gates that are not natively supported by PL (identical
# gates exist with a different name)
# TODO: remove the following when gates have been renamed in PennyLane
instruction_name = "U3Gate" if instruction_name == "UGate" else instruction_name
# Define operator builders and helpers
# operation_class -> PennyLane operation class object mapped from the Qiskit operation
# operation_args and operation_kwargs -> Parameters required for the
# instantiation of `operation_class`
operation_class = None
operation_wires = [wire_map[hash(qubit)] for qubit in qargs]
operation_kwargs = {"wires": operation_wires}
operation_args = []
# Extract the bound parameters from the operation. If the bound parameters are a
# Qiskit ParameterExpression, then replace it with the corresponding PennyLane
# variable from the unbound_params dictionary.
operation_params = _get_operation_params(instruction, unbound_params)
if instruction_name in dagger_map:
operation_class = qml.adjoint(dagger_map[instruction_name])
operation_args.extend(operation_params)
elif instruction_name in inv_map:
operation_class = getattr(pennylane_ops, inv_map[instruction_name])
operation_args.extend(operation_params)
if operation_class in (qml.QubitStateVector, qml.StatePrep):
operation_args = [np.array(operation_params)]
elif isinstance(instruction, Measure):
# Store the current operation wires and registers
op_wires, op_cregs = set(operation_wires), set(cargs)
# If final measurements are given then discriminate
# between the types of measurement encountered.
meas_terminal = False
if measurements is not None:
# Look-ahead for more gate(s) on its wire(s)
meas_terminal = True
for next_op, next_qargs, next_cargs in qc.data[idx + 1 :]:
# Check if the subsequent conditional is measurement needing
if isinstance(next_op, ControlFlowOp):
if set(next_cargs) & op_cregs:
meas_terminal = False
break
elif next_op.condition: # For legacy c_if
next_op_reg = next_op.condition[0]
if isinstance(next_op_reg, Clbit):
next_op_reg = [next_op_reg]
if set(next_op_reg) & op_cregs:
meas_terminal = False
break
# Check if the subsequent next_op is measurement interfering
if not isinstance(next_op, (Barrier, GlobalPhaseGate)):
next_op_wires = set(wire_map[hash(qubit)] for qubit in next_qargs)
# Check if there's any overlapping wires
if next_op_wires & op_wires:
meas_terminal = False
break
# Allows for adding terminal measurements
if meas_terminal:
terminal_meas.extend(operation_wires)
# Allows for queing the mid-circuit measurements
else:
operation_class = qml.measure
mid_circ_meas.append(qml.measure(wires=operation_wires))
# Allows for tracking conditional operations
for carg in cargs:
mid_circ_regs[carg] = mid_circ_meas[-1]
else:
try:
if not isinstance(instruction, (ControlFlowOp,)):
operation_args = [instruction.to_matrix()]
operation_class = qml.QubitUnitary
except (AttributeError, QiskitError):
warnings.warn(
f"{__name__}: The {instruction_name} instruction is not supported by PennyLane,"
" and has not been added to the template.",
UserWarning,
)
# Check if it is a conditional operation or conditional instruction
if instruction.condition or isinstance(instruction, ControlFlowOp):
# Iteratively recurse over to build different branches for the condition
with qml.QueuingManager.stop_recording():
branch_funcs = [
partial(load(branch_inst, measurements=None), params=params, wires=wires)
for branch_inst in operation_params
if isinstance(branch_inst, QuantumCircuit)
]
# Get the functions for handling condition
# true fns | false fns -> true | false branches
# inst_cond -> qiskit's conditional expression
true_fns, false_fns, inst_cond = _conditional_funcs(
instruction, operation_class, branch_funcs, instruction_name
)
# Process qiskit condition to PL mid-circ meas conditions
# pl_meas_conds -> PL's conditional expression with mid-circuit meas.
# length(pl_meas_conds) == len(true_fns) ==> True
pl_meas_conds = _process_condition(inst_cond, mid_circ_regs, instruction_name)
# Iterate over each of the conditional triplet and apply the condition via qml.cond
for pl_meas_cond, true_fn, false_fn in zip(pl_meas_conds, true_fns, false_fns):
qml.cond(pl_meas_cond, true_fn, false_fn)(*operation_args, **operation_kwargs)
# Check if it is not a mid-circuit measurement
elif operation_class and not isinstance(instruction, Measure):
operation_class(*operation_args, **operation_kwargs)
# Use the user-provided measurements
# an empty iterable is treated as a user-provided measurement with no measurements to queue
if measurements is not None:
if not qml.queuing.QueuingManager.active_context():
return measurements
if isinstance(measurements, Iterable):
return [qml.apply(meas) for meas in measurements]
return qml.apply(measurements)
return tuple(mid_circ_meas + list(map(qml.measure, terminal_meas))) or None
return _function
[docs]
def load_qasm(qasm_string: str):
"""Loads a PennyLane template from a QASM string.
Args:
qasm_string (str): the name of the QASM string
Returns:
function: the new PennyLane template
"""
return load(QuantumCircuit.from_qasm_str(qasm_string), measurements=[])
[docs]
def load_qasm_from_file(file: str):
"""Loads a PennyLane template from a QASM file.
Args:
file (str): the name of the QASM file
Returns:
function: the new PennyLane template
"""
return load(QuantumCircuit.from_qasm_file(file), measurements=[])
[docs]
def load_pauli_op(
pauli_op: SparsePauliOp,
params: Any = None,
wires: Union[Sequence, None] = None,
) -> qml.operation.Operator:
"""Loads a PennyLane ``Operator`` from a Qiskit `SparsePauliOp
<https://docs.quantum.ibm.com/api/qiskit/qiskit.quantum_info.SparsePauliOp>`_.
Args:
pauli_op (qiskit.quantum_info.SparsePauliOp): the ``SparsePauliOp`` to be converted
params (Any): optional assignment of coefficient values for the ``SparsePauliOp``; see the
`Qiskit documentation <https://docs.quantum.ibm.com/api/qiskit/qiskit.quantum_info.SparsePauliOp#assign_parameters>`__
to learn more about the expected format of these parameters
wires (Sequence | None): optional assignment of wires for the converted ``SparsePauliOp``;
if the original ``SparsePauliOp`` acted on :math:`N` qubits, then this must be a
sequence of length :math:`N`
Returns:
pennylane.operation.Operator: The equivalent PennyLane operator.
.. note::
The wire ordering convention differs between PennyLane and Qiskit: PennyLane wires are
enumerated from left to right, while the Qiskit convention is to enumerate from right to
left. This means a ``SparsePauliOp`` term defined by the string ``"XYZ"`` applies ``Z`` on
wire 0, ``Y`` on wire 1, and ``X`` on wire 2. For more details, see the
`String representation <https://docs.quantum.ibm.com/api/qiskit/qiskit.quantum_info.Pauli>`_
section of the Qiskit documentation for the ``Pauli`` class.
**Example**
Consider the following script which creates a Qiskit ``SparsePauliOp``:
.. code-block:: python
from qiskit.quantum_info import SparsePauliOp
qiskit_op = SparsePauliOp(["II", "XY"])
The ``SparsePauliOp`` contains two terms and acts over two qubits:
>>> qiskit_op
SparsePauliOp(['II', 'XY'],
coeffs=[1.+0.j, 1.+0.j])
To convert the ``SparsePauliOp`` into a PennyLane ``Operator``, use:
>>> from pennylane_qiskit import load_pauli_op
>>> load_pauli_op(qiskit_op)
I(0) + X(1) @ Y(0)
.. details::
:title: Usage Details
You can convert a parameterized ``SparsePauliOp`` into a PennyLane operator by assigning
literal values to each coefficient parameter. For example, the script
.. code-block:: python
import numpy as np
from qiskit.circuit import Parameter
a, b, c = [Parameter(var) for var in "abc"]
param_qiskit_op = SparsePauliOp(["II", "XZ", "YX"], coeffs=np.array([a, b, c]))
defines a ``SparsePauliOp`` with three coefficients (parameters):
>>> param_qiskit_op
SparsePauliOp(['II', 'XZ', 'YX'],
coeffs=[ParameterExpression(1.0*a), ParameterExpression(1.0*b),
ParameterExpression(1.0*c)])
The ``SparsePauliOp`` can be converted into a PennyLane operator by calling the conversion
function and specifying the value of each parameter using the ``params`` argument:
>>> load_pauli_op(param_qiskit_op, params={a: 2, b: 3, c: 4})
(
(2+0j) * I(0)
+ (3+0j) * (X(1) @ Z(0))
+ (4+0j) * (Y(1) @ X(0))
)
Similarly, a custom wire mapping can be applied to a ``SparsePauliOp`` as follows:
>>> wired_qiskit_op = SparsePauliOp("XYZ")
>>> wired_qiskit_op
SparsePauliOp(['XYZ'],
coeffs=[1.+0.j])
>>> load_pauli_op(wired_qiskit_op, wires=[3, 5, 7])
Y(5) @ Z(3) @ X(7)
"""
if not isinstance(pauli_op, SparsePauliOp):
raise ValueError(f"The operator {pauli_op} is not a valid Qiskit SparsePauliOp.")
if wires is not None and len(wires) != pauli_op.num_qubits:
raise RuntimeError(
f"The specified number of wires - {len(wires)} - does not match the "
f"number of qubits the SparsePauliOp acts on."
)
wire_map = map_wires(range(pauli_op.num_qubits), wires)
if params:
pauli_op = pauli_op.assign_parameters(params)
op_map = {"X": qml.PauliX, "Y": qml.PauliY, "Z": qml.PauliZ, "I": qml.Identity}
coeffs = pauli_op.coeffs
if ParameterExpression in [type(c) for c in coeffs]:
raise RuntimeError(f"Not all parameter expressions are assigned in coeffs {coeffs}")
qiskit_terms = pauli_op.paulis
pl_terms = []
for term in qiskit_terms:
# term is a special Qiskit type. Iterating over the term goes right to left
# in accordance with Qiskit wire order convention, i.e. `enumerate("XZ")` will be
# [(0, "Z"), (1, "X")], so we don't need to reverse to match the PL convention.
operators = [op_map[str(op)](wire_map[wire]) for wire, op in enumerate(term)]
pl_terms.append(qml.prod(*operators).simplify())
return qml.dot(coeffs, pl_terms)
# pylint:disable=protected-access
def _conditional_funcs(inst, operation_class, branch_funcs, ctrl_flow_type):
"""Builds the conditional functions for Controlled flows.
This method returns the arguments to be used by the ``qml.cond``
for creating the classically controlled flow. These are the
branches - ``true_fns`` and ``false_fns``, that contains the quantum
functions to be applied based on the results of the condition.
Additionally, we also return qiskit's classical condition,
which we convert to the corresponding PennyLane mid-circuit
measurement in the ``_process_condition`` method. These conditions
are stored in the ``condition`` attribute for all the controlled ops,
except for ``SwitchCaseOp`` for which it is stored in the ``target``
attribute. For the latter operation, we set the ``condition`` ourselves
with information from ``target`` and the information required
by us for the processing of the condition.
Args:
inst (Instruction): Qiskit's ``Instruction`` object
operation_class (Operation): PennyLane ``Operation`` for legacy controlled functionality
branch_funcs (List[partial]): Iterable of possible branching circuits for the condition.
ctrl_flow_type (str): represents the type of ``ControlledFlowOp``
Returns:
Tuple[true_fns, false_fns, condition]: the condition and the corresponding branches
"""
true_fns, false_fns = [operation_class], [None]
# Logic for using legacy c_if
if not isinstance(inst, ControlFlowOp):
return true_fns, false_fns, inst.condition
# Logic for handling IfElseOp
if ctrl_flow_type == "IfElseOp":
true_fns[0] = branch_funcs[0]
if len(branch_funcs) == 2:
false_fns[0] = branch_funcs[1]
# Logic for handling SwitchCaseOp
elif ctrl_flow_type == "SwitchCaseOp":
true_fns, res_bits = [], []
for case, b_idx in inst._case_map.items():
if not isinstance(case, _DefaultCaseType):
true_fns.append(branch_funcs[b_idx])
res_bits.append(case)
# Switch ops condition is None by default
# So we make up a custom one for it ourselves
inst.condition = [inst.target, res_bits, "SwitchCase"]
if any((isinstance(case, _DefaultCaseType) for case in inst._case_map)):
true_fns.append(branch_funcs[-1])
# Marker for we have a default case scenario
inst.condition[-1] = "SwitchDefault"
false_fns = [None] * len(true_fns)
return true_fns, false_fns, inst.condition
def _process_condition(cond_op, mid_circ_regs, instruction_name):
"""Process the condition to corresponding measurement value.
In Qiskit, the generic form of condition is of two types:
1. ``tuple[ClassicalRegister, int] or tuple[Clbit, int]``
2. ``expr.Expr``
In addition for this, we have another custom type:
3. ``List(Target: Condition, Vals: List[Int], Type: str)``
Args:
cond_op (condition): condition as described above
mid_circ_regs (dict): dictionary that maps the utilized qiskit's classical bits
to the performed PennyLane's mid-circuit measurements
instruction_name (str): represents the name of the instruction. Used in raising
an informative warning in case processing of the condition fails.
Returns:
pl_meas: list of corresponding mid-circuit measurements to be used in ``qml.cond``
"""
# container for PL measurements operators
pl_meas = []
condition = cond_op
# Check if the condition is as a tuple -> (Clbit/Clreg, Val)
if isinstance(condition, tuple):
clbits = [condition[0]] if isinstance(condition[0], Clbit) else list(condition[0])
# Proceed only if we have access to all conditioned classical bits
if all(clbit in mid_circ_regs for clbit in clbits):
pl_meas.append(
sum(2**idx * mid_circ_regs[clbit] for idx, clbit in enumerate(clbits))
== condition[1]
)
# Check if the condition is coming form a SwitchCase -> (Target, Vals, Type)
if isinstance(condition, list):
meas_pl_ops = _process_switch_condition(condition, mid_circ_regs)
pl_meas.extend(meas_pl_ops)
# Check if the condition is an Expr
if isinstance(condition, expr.Expr):
meas_pl_op = _expr_evaluation(condition, mid_circ_regs)
if meas_pl_op is not None:
pl_meas.append(meas_pl_op)
# Check if were able to add the meas values
# Else raise a warning before returning
if pl_meas:
return pl_meas
warnings.warn(
f"The provided {condition} for {instruction_name} uses additional classical information that cannot be returned or processed.",
UserWarning,
)
return pl_meas
def _process_switch_condition(condition, mid_circ_regs):
"""Helper method for processing condition for SwtichCaseOp.
Args:
condition (condition): condition as described in ``_process_condition`` of the
third type - ``List(Target: Condition, Vals: List[Int], Type: str)``
mid_circ_regs (dict): dictionary that maps the utilized qiskit's classical bits
to the performed PennyLane's mid-circuit measurements
Returns:
meas_pl_ops: list of corresponding mid-circuit measurements to be used in ``qml.cond``
"""
# if the target is not an Expr
if not isinstance(condition[0], expr.Expr):
# Prepare the classical bits used for the condition
clbits = [condition[0]] if isinstance(condition[0], Clbit) else list(condition[0])
# Proceed only if we have access to all conditioned classical bits
meas_pl_op = None
if all(clbit in mid_circ_regs for clbit in clbits):
# Build an integer representation for each switch case
meas_pl_op = sum(2**idx * mid_circ_regs[clbit] for idx, clbit in enumerate(clbits))
# if the target is an Expr
else:
meas_pl_op = _expr_evaluation(condition[0], mid_circ_regs)
meas_pl_ops = []
if meas_pl_op is not None:
# Add a measurement for each of the switch cases
meas_pl_ops.extend([meas_pl_op == clval for clval in condition[1]])
# If we have default case, add an additional measurement for it
if condition[2] == "SwitchDefault":
meas_pl_ops.append(
reduce(
lambda m0, m1: m0 & m1,
[(meas_pl_op != clval) for clval in condition[1]],
)
)
return meas_pl_ops
# pylint:disable = unbalanced-tuple-unpacking
def _expr_evaluation(condition, mid_circ_regs):
"""Evaluates the ``Expr`` condition
Args:
condition (condition): condition as described in ``_process_condition``
of the second type - ``Expr``
mid_circ_regs (dict): dictionary that maps the utilized qiskit's classical bits
to the performed PennyLane's mid-circuit measurements
Returns:
condition_res: corresponding mid-circuit measurements to be used in ``qml.cond``
"""
# Maps qiskit `expr` names to their mathematical logic
_expr_mapping = {
"BIT_AND": lambda meas1, meas2: meas1 & meas2,
"BIT_OR": lambda meas1, meas2: meas1 | meas2,
"BIT_XOR": lambda meas1, meas2: meas1 ^ meas2,
"LOGIC_AND": lambda meas1, meas2: meas1 and meas2,
"LOGIC_OR": lambda meas1, meas2: meas1 or meas2,
"EQUAL": lambda meas1, meas2: meas1 == meas2,
"NOT_EQUAL": lambda meas1, meas2: meas1 != meas2,
"LESS": lambda meas1, meas2: meas1 < meas2,
"LESS_EQUAL": lambda meas1, meas2: meas1 <= meas2,
"GREATER": lambda meas1, meas2: meas1 > meas2,
"GREATER_EQUAL": lambda meas1, meas2: meas1 >= meas2,
}
# Get the left and right classical controls
cond1, cond2 = condition.left, condition.right
# Iterate over each and extract classical bits
clbits, clvals = [], []
for _, carg in enumerate([cond1, cond2]):
# We don't need to work with Qiskit's Cast expr op,
# as we'll be casting stuff manually by ourselves.
if isinstance(carg, expr.Cast):
carg = carg.operand
if isinstance(carg, expr.Value):
clvals.append([carg.value])
elif isinstance(carg, expr.Var):
clbits.append([carg.var] if isinstance(carg.var, Clbit) else list(carg.var))
# Proceed only if we have access to all conditioned classical bits
for idx, clreg in enumerate(clbits):
if not all(clbit in mid_circ_regs for clbit in clreg):
return None
clbits[idx] = [mid_circ_regs[clbit] for clbit in clreg]
# Flag for tracking if it is a bitwise operation.
# bitwise = true -> apply on each bit of the binary forms
# bitwise = false -> apply on the integer forms as whole
bitwise_flag = False
condition_name = condition.op.name
if condition_name[:3] == "BIT":
bitwise_flag = True
# divide the bits among left and right cbit registers
if len(clbits) == 2:
condition_res = _expr_eval_clregs(clbits, _expr_mapping[condition_name], bitwise_flag)
# divide the bits into a cbit register and integer
else:
condition_res = _expr_eval_clvals(
clbits, clvals, _expr_mapping[condition_name], bitwise_flag
)
return condition_res
def _expr_eval_clregs(clbits, expr_func, bitwise=False):
"""Helper method for ``Expr`` evaluation when two registers are present.
Args:
clbits (List[List[int], List[int]]): list of two registers represented by the
corresponding mid-circuit measurements mapped from their classical bits.
expr_func (lambda): mapped lambda func from ``_expr_mapping`` in the ``_expr_evaluation``
method that performs the corresponding mathematical logic.
bitwise (bool): flag that specifies if the ``expr_func`` is performed on individual bits.
Returns:
condition_res: corresponding mid-circuit measurements to be used in ``qml.cond``
"""
clreg1, clreg2 = clbits
# Make both the bits of the same width with padding
# We swap the registers so that we only have to pad right one.
if len(clreg1) < len(clreg2):
clreg1, clreg2 = clreg2, clreg1
clreg2 = [0] * (len(clreg2) - len(clreg1)) + clreg2
# For bitwise operations we need to work with individual bits
# So we build an integer form 'after' performing the operation.
if bitwise:
condition_res = sum(
2**idx * expr_func(meas1, meas2)
for idx, (meas1, meas2) in enumerate(zip(clreg1, clreg2))
)
# For other operations we need to work with all bits at once,
# So we build an integer form 'before' performing the operation.
else:
meas1, meas2 = [
sum(2**idx * meas for idx, meas in enumerate(clreg)) for clreg in [clreg1, clreg2]
]
condition_res = expr_func(meas1, meas2)
return condition_res
def _expr_eval_clvals(clbits, clvals, expr_func, bitwise=False):
"""Helper method for ``Expr`` evaluation when one register and one integer value is present.
Args:
clbits (List[List[int]]): list of two registers represented by the
corresponding mid-circuit measurements mapped from their classical bits.
clvals (List[List[int]])
expr_func (lambda): mapped lambda func from ``_expr_mapping`` in the ``_expr_evaluation``
method that performs the corresponding mathematical logic.
bitwise (bool): flag that specifies if the ``expr_func`` is performed on individual bits.
Returns:
condition_res: corresponding mid-circuit measurements to be used in ``qml.cond``
"""
[clreg1], [[clreg2]] = clbits, clvals
# For bitwise operations, we first need a binary form for clreg2
if bitwise:
# Number of bits should be max of the binary-rep of the clvals or clreg.
num_bits = max(len(clreg1), int(np.ceil(np.log2(clreg2))))
clreg2 = map(int, np.binary_repr(clreg2, width=num_bits))
clreg1 = [0] * (num_bits - len(clreg1)) + clreg1
condition_res = sum(
2**idx * expr_func(meas1, meas2)
for idx, (meas1, meas2) in enumerate(zip(clreg1, clreg2))
)
# For other operations, we just need the integer form of clreg1
else:
meas1 = sum(2**idx * meas for idx, meas in enumerate(clreg1))
condition_res = expr_func(meas1, clreg2)
return condition_res
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