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#
# Licensed under the Apache License, Version 2.0 (the "License"). You
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#
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from __future__ import annotations
import numbers
from collections.abc import Sequence
from copy import deepcopy
from typing import Union
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.qubit_set import QubitSet
[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)
self._coef = 1
def _unscaled(self) -> Observable:
return Observable(qubit_count=self.qubit_count, ascii_symbols=self.ascii_symbols)
[docs]
def to_ir(
self,
target: QubitSet | None = None,
ir_type: IRType = IRType.JAQCD,
serialization_properties: SerializationProperties | None = None,
) -> Union[str, list[Union[str, list[list[list[float]]]]]]:
"""Returns the IR representation for the observable
Args:
target (QubitSet | 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:
Union[str, list[Union[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()
elif 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
)
else:
raise ValueError(f"Supplied ir_type {ir_type} is not supported.")
def _to_jaqcd(self) -> list[Union[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,
target: QubitSet | 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.
target (QubitSet | 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 coefficient(self) -> int:
"""The coefficient of the observable.
Returns:
int: coefficient value of the observable.
"""
return self._coef
@property
def basis_rotation_gates(self) -> tuple[Gate, ...]:
"""Returns the basis rotation gates for this observable.
Returns:
tuple[Gate, ...]: The basis rotation gates for this observable.
"""
raise NotImplementedError
@property
def eigenvalues(self) -> np.ndarray:
"""Returns the eigenvalues of this observable.
Returns:
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 ValueError("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 ValueError("Can only perform addition between observables.")
return Observable.Sum([self, other])
def __sub__(self, other: Observable):
if not isinstance(other, Observable):
raise ValueError("Can only perform subtraction between observables.")
return self + (-1 * other)
def __repr__(self) -> str:
return f"{self.name}('qubit_count': {self.qubit_count})"
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]):
super().__init__(qubit_count=1, ascii_symbols=ascii_symbols)
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
)