# Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file 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.
from __future__ import annotations
import numbers
from collections.abc import Sequence
from copy import deepcopy
import numpy as np
from braket.circuits.gate import Gate
from braket.circuits.quantum_operator import QuantumOperator
from braket.circuits.serialization import (
IRType,
OpenQASMSerializationProperties,
SerializationProperties,
)
from braket.registers import QubitInput, QubitSet, QubitSetInput
EULER_OBSERVABLE_PREFIX = "_OBSERVABLE_"
EULER_Z1_PREFIX = f"{EULER_OBSERVABLE_PREFIX}THETA_"
EULER_X_PREFIX = f"{EULER_OBSERVABLE_PREFIX}PHI_"
EULER_Z2_PREFIX = f"{EULER_OBSERVABLE_PREFIX}OMEGA_"
[docs]
class Observable(QuantumOperator):
"""Class `Observable` to represent a quantum observable.
Objects of this type can be used as input to `ResultType.Sample`, `ResultType.Variance`,
`ResultType.Expectation` to specify the measurement basis.
"""
def __init__(
self, qubit_count: int, ascii_symbols: Sequence[str], targets: QubitSetInput | None = None
):
super().__init__(qubit_count=qubit_count, ascii_symbols=ascii_symbols)
targets = QubitSet(targets)
if targets and (num_targets := len(targets)) != qubit_count:
raise ValueError(
f"Length of target {num_targets} does not match qubit count {qubit_count}"
)
self._targets = targets
self._coef = 1
def _unscaled(self) -> Observable:
return Observable(
qubit_count=self.qubit_count, ascii_symbols=self.ascii_symbols, targets=self._targets
)
[docs]
def to_ir(
self,
target: QubitSetInput | None = None,
ir_type: IRType = IRType.JAQCD,
serialization_properties: SerializationProperties | None = None,
) -> str | list[str | list[list[list[float]]]]:
"""Returns the IR representation for the observable
Args:
target (QubitSetInput | None): target qubit(s). Defaults to None.
ir_type(IRType) : The IRType to use for converting the result type object to its
IR representation. Defaults to IRType.JAQCD.
serialization_properties (SerializationProperties | None): The serialization properties
to use while serializing the object to the IR representation. The serialization
properties supplied must correspond to the supplied `ir_type`. Defaults to None.
Returns:
str | list[str | list[list[list[float]]]]: The IR representation for
the observable.
Raises:
ValueError: If the supplied `ir_type` is not supported, or if the supplied serialization
properties don't correspond to the `ir_type`.
"""
if ir_type == IRType.JAQCD:
return self._to_jaqcd()
if ir_type == IRType.OPENQASM:
if serialization_properties and not isinstance(
serialization_properties, OpenQASMSerializationProperties
):
raise ValueError(
"serialization_properties must be of type OpenQASMSerializationProperties "
"for IRType.OPENQASM."
)
return self._to_openqasm(
serialization_properties or OpenQASMSerializationProperties(), target
)
raise ValueError(f"Supplied ir_type {ir_type} is not supported.")
def _to_jaqcd(self) -> list[str | list[list[list[float]]]]:
"""Returns the JAQCD representation of the observable."""
raise NotImplementedError("to_jaqcd has not been implemented yet.")
def _to_openqasm(
self,
serialization_properties: OpenQASMSerializationProperties,
targets: QubitSetInput | None = None,
) -> str:
"""Returns the openqasm string representation of the result type.
Args:
serialization_properties (OpenQASMSerializationProperties): The serialization properties
to use while serializing the object to the IR representation.
targets (QubitSetInput | None): target qubit(s). Defaults to None.
Returns:
str: Representing the openqasm representation of the result type.
"""
raise NotImplementedError("to_openqasm has not been implemented yet.")
@property
def targets(self) -> QubitSet | None:
"""QubitSet | None: The target qubits of this observable
If `None`, this is provided by the enclosing result type.
"""
return self._targets
@property
def coefficient(self) -> int:
"""int: coefficient value of the observable."""
return self._coef
@property
def basis_rotation_gates(self) -> tuple[Gate, ...]:
"""tuple[Gate, ...]: The basis rotation gates for this observable."""
raise NotImplementedError
@property
def euler_angles(self) -> dict[str, float]:
"""dict[str, float]: A mapping of standardized free parameter name to ZXZ Euler angle value
that diagonalizes this observable."""
raise NotImplementedError
[docs]
@staticmethod
def get_euler_angles(targets: QubitSetInput) -> dict[str, float]:
"""Get the ZXZ Euler angle mapping of this observable for the given qubit.
Args:
targets (QubitSetInput): The target qubits; this is used for the parameter names in the
output mapping.
Returns:
dict[str, float]: A mapping of standardized free parameter name to ZXZ Euler angle value
that diagonalizes this observable.
"""
raise NotImplementedError
@property
def eigenvalues(self) -> np.ndarray:
"""np.ndarray: The eigenvalues of this observable."""
raise NotImplementedError
[docs]
def eigenvalue(self, index: int) -> float:
"""Returns the eigenvalue of this observable at the given index.
The eigenvalues are ordered by their corresponding computational basis state
after diagonalization.
Args:
index (int): The index of the desired eigenvalue
Returns:
float: The `index` th eigenvalue of the observable.
"""
raise NotImplementedError
[docs]
@classmethod
def register_observable(cls, observable: Observable) -> None:
"""Register an observable implementation by adding it into the `Observable` class.
Args:
observable (Observable): Observable class to register.
"""
setattr(cls, observable.__name__, observable)
def __matmul__(self, other: Observable) -> Observable.TensorProduct:
if isinstance(other, Observable):
return Observable.TensorProduct([self, other])
raise TypeError("Can only perform tensor products between observables.")
def __mul__(self, other: Observable) -> Observable:
"""Scalar multiplication"""
if isinstance(other, numbers.Number):
observable_copy = deepcopy(self)
observable_copy._coef *= other
return observable_copy
raise TypeError("Observable coefficients must be numbers.")
def __rmul__(self, other: Observable) -> Observable:
return self * other
def __add__(self, other: Observable):
if not isinstance(other, Observable):
raise TypeError("Can only perform addition between observables.")
return Observable.Sum([self, other])
def __sub__(self, other: Observable):
if not isinstance(other, Observable):
raise TypeError("Can only perform subtraction between observables.")
return self + (-1 * other)
def __repr__(self) -> str:
return (
f"{self.name}('qubit_count': {self._qubit_count})"
if not self._targets
else f"{self.name}('qubit_count': {self._qubit_count}, 'target': {self._targets})"
)
def __eq__(self, other: Observable) -> bool:
if isinstance(other, Observable):
return self.name == other.name
return NotImplemented
[docs]
class StandardObservable(Observable):
"""Class `StandardObservable` to represent a Pauli-like quantum observable with
eigenvalues of (+1, -1).
"""
def __init__(self, ascii_symbols: Sequence[str], target: QubitInput | None = None):
super().__init__(
qubit_count=1,
ascii_symbols=ascii_symbols,
targets=[target] if target is not None else None,
)
self._eigenvalues = (1.0, -1.0) # immutable
def _unscaled(self) -> StandardObservable:
return StandardObservable(ascii_symbols=self.ascii_symbols)
@property
def eigenvalues(self) -> np.ndarray:
return self.coefficient * np.array(self._eigenvalues)
[docs]
def eigenvalue(self, index: int) -> float:
return self.coefficient * self._eigenvalues[index]
@property
def ascii_symbols(self) -> tuple[str, ...]:
return tuple(
f"{self.coefficient if self.coefficient != 1 else ''}{ascii_symbol}"
for ascii_symbol in self._ascii_symbols
)
[docs]
def euler_angle_parameter_names(target: QubitInput) -> tuple[str, str, str]:
qubit = str(int(target))
return (
f"{EULER_Z1_PREFIX}{qubit}",
f"{EULER_X_PREFIX}{qubit}",
f"{EULER_Z2_PREFIX}{qubit}",
)