cirq.PauliSum

Represents operator defined by linear combination of PauliStrings.

cirq.PauliSum(
    linear_dict: Optional[value.LinearDict[UnitPauliStringT]] = None
)

Since PauliStrings store their own coefficients, this class does not implement the LinearDict interface. Instead, you can add and subtract terms and then iterate over the resulting (simplified) expression.

Under the hood, this class is backed by a LinearDict with coefficient-less PauliStrings as keys. PauliStrings are reconstructed on-the-fly during iteration.

qubits

Methods

copy

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copy() -> 'PauliSum'

expectation_from_density_matrix

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expectation_from_density_matrix(
    state: np.ndarray,
    qubit_map: Mapping[cirq.Qid, int],
    *,
    atol: float = 1e-07,
    check_preconditions: bool = True
) -> float

Evaluate the expectation of this PauliSum given a density matrix.

See PauliString.expectation_from_density_matrix.

Args
state An array representing a valid density matrix.
qubit_map A map from all qubits used in this PauliSum to the indices of the qubits that state is defined over.
atol Absolute numerical tolerance.
check_preconditions Whether to check that state represents a valid density matrix.

Returns
The expectation value of the input state.

Raises
NotImplementedError If any of the coefficients are imaginary, so that this is not Hermitian.
TypeError If the input state is not a complex type.
ValueError If the input vector is not the correct size or shape.

expectation_from_state_vector

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expectation_from_state_vector(
    state_vector: np.ndarray,
    qubit_map: Mapping[cirq.Qid, int],
    *,
    atol: float = 1e-07,
    check_preconditions: bool = True
) -> float

Evaluate the expectation of this PauliSum given a state vector.

See PauliString.expectation_from_state_vector.

Args
state_vector An array representing a valid state vector.
qubit_map A map from all qubits used in this PauliSum to the indices of the qubits that state_vector is defined over.
atol Absolute numerical tolerance.
check_preconditions Whether to check that state_vector represents a valid state vector.

Returns
The expectation value of the input state.

Raises
NotImplementedError If any of the coefficients are imaginary, so that this is not Hermitian.
TypeError If the input state is not a complex type.
ValueError If the input vector is not the correct size or shape.

from_boolean_expression

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@classmethod
from_boolean_expression(
    boolean_expr: Expr, qubit_map: Dict[str, 'cirq.Qid']
) -> 'PauliSum'

Builds the Hamiltonian representation of a Boolean expression.

This is based on "On the representation of Boolean and real functions as Hamiltonians for quantum computing" by Stuart Hadfield, https://arxiv.org/abs/1804.09130

Args
boolean_expr A Sympy expression containing symbols and Boolean operations
qubit_map map of string (boolean variable name) to qubit.

Return
The PauliString that represents the Boolean expression.

Raises
ValueError If boolean_expr is of an unsupported type.

from_pauli_strings

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@classmethod
from_pauli_strings(
    terms: Union[PauliString, List[PauliString]]
) -> 'PauliSum'

matrix

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matrix(
    qubits: Optional[Iterable[raw_types.Qid]] = None
) -> np.ndarray

Reconstructs matrix of self from underlying Pauli operations in computational basis of qubits.

Raises
TypeError if any of the gates in self does not provide a unitary.

with_qubits

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with_qubits(
    *new_qubits
) -> 'PauliSum'

wrap

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@staticmethod
wrap(
    val: cirq.PauliSumLike
) -> 'PauliSum'

__add__

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__add__(
    other
)

__bool__

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__bool__() -> bool

__eq__

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__eq__(
    other: _SupportsValueEquality
) -> bool

__iter__

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__iter__()

__len__

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__len__() -> int

__mul__

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__mul__(
    other: cirq.PauliSumLike
)

__neg__

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__neg__()

__pow__

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__pow__(
    exponent: int
)

__radd__

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__radd__(
    other
)

__rmul__

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__rmul__(
    other: cirq.PauliSumLike
)

__rsub__

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__rsub__(
    other
)

__sub__

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__sub__(
    other
)

__truediv__

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__truediv__(
    a: value.Scalar
)