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# Licensed under the Apache License, Version 2.0 (the "License"). You
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from __future__ import annotations
from typing import List, Sequence, Tuple, Union
import numpy as np
from braket.circuits.gate import Gate
from braket.circuits.quantum_operator import QuantumOperator
from braket.circuits.quantum_operator_helpers import get_pauli_eigenvalues
[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]):
super().__init__(qubit_count=qubit_count, ascii_symbols=ascii_symbols)
[docs] def to_ir(self) -> List[Union[str, List[List[List[float]]]]]:
"""List[Union[str, List[List[List[float]]]]]: Returns the IR
representation for the observable"""
raise NotImplementedError
@property
def basis_rotation_gates(self) -> Tuple[Gate]:
"""Tuple[Gate]: Returns the basis rotation gates for this observable."""
raise NotImplementedError
@property
def eigenvalues(self) -> np.ndarray:
"""np.ndarray: Returns the eigenvalues of this 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.TensorProduct:
if isinstance(other, Observable.TensorProduct):
return other.__rmatmul__(self)
if isinstance(other, Observable):
return Observable.TensorProduct([self, other])
raise ValueError("Can only perform tensor products between observables.")
def __repr__(self) -> str:
return f"{self.name}('qubit_count': {self.qubit_count})"
def __eq__(self, other) -> bool:
if isinstance(other, Observable):
return self.name == other.name
return NotImplemented
[docs]class StandardObservable(Observable):
"""
Class `StandardObservable` to represent a standard quantum observable with
eigenvalues of +/-1, each with a multiplicity of 1.
"""
def __init__(self, qubit_count: int, ascii_symbols: Sequence[str]):
super().__init__(qubit_count=qubit_count, ascii_symbols=ascii_symbols)
@property
def eigenvalues(self) -> np.ndarray:
return get_pauli_eigenvalues(self.qubit_count)