Quellcode für qiskit.opflow.state_fns.operator_state_fn

# 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
# 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.

""" OperatorStateFn Class """

from typing import List, Optional, Set, Union, cast

import numpy as np

from qiskit.circuit import ParameterExpression
from qiskit.opflow.list_ops.list_op import ListOp
from qiskit.opflow.list_ops.summed_op import SummedOp
from qiskit.opflow.list_ops.tensored_op import TensoredOp
from qiskit.opflow.operator_base import OperatorBase
from qiskit.opflow.primitive_ops.matrix_op import MatrixOp
from qiskit.opflow.primitive_ops.pauli_sum_op import PauliSumOp
from qiskit.opflow.state_fns.state_fn import StateFn
from qiskit.opflow.state_fns.circuit_state_fn import CircuitStateFn
from qiskit.quantum_info import Statevector

[Doku]class OperatorStateFn(StateFn): r""" A class for state functions and measurements which are defined by a density Operator, stored using an ``OperatorBase``. """ primitive: OperatorBase # TODO allow normalization somehow? def __init__( self, primitive: OperatorBase, coeff: Union[complex, ParameterExpression] = 1.0, is_measurement: bool = False, ) -> None: """ Args: primitive: The ``OperatorBase`` which defines the behavior of the underlying State function. coeff: A coefficient by which to multiply the state function is_measurement: Whether the StateFn is a measurement operator """ super().__init__(primitive, coeff=coeff, is_measurement=is_measurement)
[Doku] def primitive_strings(self) -> Set[str]: return self.primitive.primitive_strings()
@property def num_qubits(self) -> int: return self.primitive.num_qubits
[Doku] def add(self, other: OperatorBase) -> Union["OperatorStateFn", SummedOp]: if not self.num_qubits == other.num_qubits: raise ValueError( "Sum over statefns with different numbers of qubits, {} and {}, is not well " "defined".format(self.num_qubits, other.num_qubits) ) # Right now doesn't make sense to add a StateFn to a Measurement if isinstance(other, OperatorStateFn) and self.is_measurement == other.is_measurement: if isinstance(other.primitive, OperatorBase) and self.primitive == other.primitive: return OperatorStateFn( self.primitive, coeff=self.coeff + other.coeff, is_measurement=self.is_measurement, ) # Covers Statevector and custom. elif isinstance(other, OperatorStateFn): # Also assumes scalar multiplication is available return OperatorStateFn( (self.coeff * self.primitive).add(other.primitive * other.coeff), is_measurement=self._is_measurement, ) return SummedOp([self, other])
[Doku] def adjoint(self) -> "OperatorStateFn": return OperatorStateFn( self.primitive.adjoint(), coeff=self.coeff.conjugate(), is_measurement=(not self.is_measurement), )
def _expand_dim(self, num_qubits: int) -> "OperatorStateFn": return OperatorStateFn( self.primitive._expand_dim(num_qubits), coeff=self.coeff, is_measurement=self.is_measurement, )
[Doku] def permute(self, permutation: List[int]) -> "OperatorStateFn": return OperatorStateFn( self.primitive.permute(permutation), coeff=self.coeff, is_measurement=self.is_measurement, )
[Doku] def tensor(self, other: OperatorBase) -> Union["OperatorStateFn", TensoredOp]: if isinstance(other, OperatorStateFn): return OperatorStateFn( self.primitive.tensor(other.primitive), coeff=self.coeff * other.coeff, is_measurement=self.is_measurement, ) return TensoredOp([self, other])
[Doku] def to_density_matrix(self, massive: bool = False) -> np.ndarray: """Return numpy matrix of density operator, warn if more than 16 qubits to force the user to set massive=True if they want such a large matrix. Generally big methods like this should require the use of a converter, but in this case a convenience method for quick hacking and access to classical tools is appropriate.""" OperatorBase._check_massive("to_density_matrix", True, self.num_qubits, massive) return self.primitive.to_matrix() * self.coeff
[Doku] def to_matrix_op(self, massive: bool = False) -> "OperatorStateFn": """Return a MatrixOp for this operator.""" return OperatorStateFn( self.primitive.to_matrix_op(massive=massive) * self.coeff, is_measurement=self.is_measurement, )
[Doku] def to_matrix(self, massive: bool = False) -> np.ndarray: r""" Note: this does not return a density matrix, it returns a classical matrix containing the quantum or classical vector representing the evaluation of the state function on each binary basis state. Do not assume this is is a normalized quantum or classical probability vector. If we allowed this to return a density matrix, then we would need to change the definition of composition to be ~Op @ StateFn @ Op for those cases, whereas by this methodology we can ensure that composition always means Op @ StateFn. Return numpy vector of state vector, warn if more than 16 qubits to force the user to set massive=True if they want such a large vector. Args: massive: Whether to allow large conversions, e.g. creating a matrix representing over 16 qubits. Returns: np.ndarray: Vector of state vector Raises: ValueError: Invalid parameters. """ OperatorBase._check_massive("to_matrix", False, self.num_qubits, massive) # Operator - return diagonal (real values, not complex), # not rank 1 decomposition (statevector)! mat = self.primitive.to_matrix(massive=massive) # TODO change to weighted sum of eigenvectors' StateFns? # ListOp primitives can return lists of matrices (or trees for nested ListOps), # so we need to recurse over the # possible tree. def diag_over_tree(op): if isinstance(op, list): return [diag_over_tree(o) for o in op] else: vec = np.diag(op) * self.coeff # Reshape for measurements so still works for composition. return vec if not self.is_measurement else vec.reshape(1, -1) return diag_over_tree(mat)
[Doku] def to_circuit_op(self): r"""Return ``StateFnCircuit`` corresponding to this StateFn. Ignore for now because this is undefined. TODO maybe call to_pauli_op and diagonalize here, but that could be very inefficient, e.g. splitting one Stabilizer measurement into hundreds of 1 qubit Paulis.""" raise NotImplementedError
def __str__(self) -> str: prim_str = str(self.primitive) if self.coeff == 1.0: return "{}({})".format( "OperatorStateFn" if not self.is_measurement else "OperatorMeasurement", prim_str ) else: return "{}({}) * {}".format( "OperatorStateFn" if not self.is_measurement else "OperatorMeasurement", prim_str, self.coeff, )
[Doku] def eval( self, front: Optional[Union[str, dict, np.ndarray, OperatorBase, Statevector]] = None ) -> Union[OperatorBase, complex]: if front is None: matrix = cast(MatrixOp, self.primitive.to_matrix_op()) # pylint: disable=cyclic-import from .vector_state_fn import VectorStateFn return VectorStateFn(matrix[0, :]) if not self.is_measurement and isinstance(front, OperatorBase): raise ValueError( "Cannot compute overlap with StateFn or Operator if not Measurement. Try taking " "sf.adjoint() first to convert to measurement." ) if not isinstance(front, OperatorBase): front = StateFn(front) if isinstance(self.primitive, ListOp) and self.primitive.distributive: evals = [ OperatorStateFn(op, is_measurement=self.is_measurement).eval(front) for op in self.primitive.oplist ] result = self.primitive.combo_fn(evals) if isinstance(result, list): multiplied = self.primitive.coeff * self.coeff * np.array(result) return multiplied.tolist() return result * self.coeff * self.primitive.coeff # pylint: disable=cyclic-import from .vector_state_fn import VectorStateFn if isinstance(self.primitive, PauliSumOp) and isinstance(front, VectorStateFn): return ( front.primitive.expectation_value(self.primitive.primitive) * self.coeff * front.coeff ) # Need an ListOp-specific carve-out here to make sure measurement over a ListOp doesn't # produce two-dimensional ListOp from composing from both sides of primitive. # Can't use isinstance because this would include subclasses. # pylint: disable=unidiomatic-typecheck if isinstance(front, ListOp) and type(front) == ListOp: return front.combo_fn( [self.eval(front.coeff * front_elem) for front_elem in front.oplist] ) # If we evaluate against a circuit, evaluate it to a vector so we # make sure to only do the expensive circuit simulation once if isinstance(front, CircuitStateFn): front = front.eval() return front.adjoint().eval(cast(OperatorBase, self.primitive.eval(front))) * self.coeff
[Doku] def sample(self, shots: int = 1024, massive: bool = False, reverse_endianness: bool = False): raise NotImplementedError