def expectation_from_state_vector(
self,
state_vector: np.ndarray,
qubit_map: Mapping[raw_types.Qid, int],
*,
atol: float = 1e-7,
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.
"""
if any(abs(p.coefficient.imag) > 0.0001 for p in self):
raise NotImplementedError(
"Cannot compute expectation value of a non-Hermitian "
"PauliString <{}>. Coefficient must be real.".format(self))
# TODO: Avoid enforce specific complex type. This is necessary to
# prevent an `apply_unitary` bug.
# Github issue: https://github.com/quantumlib/Cirq/issues/2041
if state_vector.dtype.kind != 'c':
raise TypeError(
"Input state dtype must be np.complex64 or np.complex128")
size = state_vector.size
num_qubits = size.bit_length() - 1
_validate_qubit_mapping(qubit_map, self.qubits, num_qubits)
if len(state_vector.shape) != 1 and state_vector.shape != (
2, ) * num_qubits:
raise ValueError("Input array does not represent a state vector "
"with shape `(2 ** n,)` or `(2, ..., 2)`.")
if check_preconditions:
qis.validate_normalized_state_vector(
state_vector=state_vector,
qid_shape=(2, ) * num_qubits,
dtype=state_vector.dtype,
atol=atol,
)
return sum(
p._expectation_from_state_vector_no_validation(
state_vector, qubit_map) for p in self)
def expectation_from_density_matrix(
self,
state: np.ndarray,
qubit_map: Mapping[raw_types.Qid, int],
*,
atol: float = 1e-7,
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.
"""
if any(abs(p.coefficient.imag) > 0.0001 for p in self):
raise NotImplementedError(
"Cannot compute expectation value of a non-Hermitian "
"PauliString <{}>. Coefficient must be real.".format(self))
# FIXME: Avoid enforce specific complex type. This is necessary to
# prevent an `apply_unitary` bug (Issue #2041).
if state.dtype.kind != 'c':
raise TypeError(
"Input state dtype must be np.complex64 or np.complex128")
size = state.size
num_qubits = int(np.sqrt(size)).bit_length() - 1
_validate_qubit_mapping(qubit_map, self.qubits, num_qubits)
dim = int(np.sqrt(size))
if state.shape != (dim, dim) and state.shape != (2, 2) * num_qubits:
raise ValueError("Input array does not represent a density matrix "
"with shape `(2 ** n, 2 ** n)` or `(2, ..., 2)`.")
if check_preconditions:
# Do not enforce reshaping if the state all axes are dimension 2.
_ = qis.to_valid_density_matrix(
density_matrix_rep=state.reshape(dim, dim),
num_qubits=num_qubits,
dtype=state.dtype,
atol=atol,
)
return sum(
p._expectation_from_density_matrix_no_validation(state, qubit_map)
for p in self)
def expectation_from_wavefunction(
self,
state: np.ndarray,
qubit_map: Mapping[raw_types.Qid, int],
*,
atol: float = 1e-7,
check_preconditions: bool = True) -> float:
"""Evaluate the expectation of this PauliSum given a wavefunction.
See `PauliString.expectation_from_wavefunction`.
Args:
state: An array representing a valid wavefunction.
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 wavefunction.
Returns:
The expectation value of the input state.
"""
if any(abs(p.coefficient.imag) > 0.0001 for p in self):
raise NotImplementedError(
"Cannot compute expectation value of a non-Hermitian "
"PauliString <{}>. Coefficient must be real.".format(self))
# FIXME: Avoid enforce specific complex type. This is necessary to
# prevent an `apply_unitary` bug (Issue #2041).
if state.dtype.kind != 'c':
raise TypeError("Input state dtype must be np.complex64 or "
"np.complex128")
size = state.size
num_qubits = size.bit_length() - 1
_validate_qubit_mapping(qubit_map, self.qubits, num_qubits)
if len(state.shape) != 1 and state.shape != (2, ) * num_qubits:
raise ValueError("Input array does not represent a wavefunction "
"with shape `(2 ** n,)` or `(2, ..., 2)`.")
if check_preconditions:
# HACK: avoid circular import
from cirq.sim.wave_function import validate_normalized_state
validate_normalized_state(state=state,
qid_shape=(2, ) * num_qubits,
dtype=state.dtype,
atol=atol)
return sum(
p._expectation_from_wavefunction_no_validation(state, qubit_map)
for p in self)
def expectation_from_density_matrix(self, state: np.ndarray,
qubit_map: Mapping[raw_types.Qid, int]
) -> 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.
Returns:
The expectation value of the input state.
"""
if any(abs(p.coefficient.imag) > 0.0001 for p in self):
raise NotImplementedError(
"Cannot compute expectation value of a non-Hermitian "
"PauliString <{}>. Coefficient must be real.".format(self))
# FIXME: Avoid enforce specific complex type. This is necessary to
# prevent an `apply_unitary` bug (Issue #2041).
if state.dtype.kind != 'c':
raise TypeError("Input state dtype must be np.complex64 or "
"np.complex128")
size = state.size
num_qubits = int(np.sqrt(size)).bit_length() - 1
_validate_qubit_mapping(qubit_map, self.qubits, num_qubits)
dim = int(np.sqrt(size))
if state.shape != (dim, dim) and state.shape != (2, 2) * num_qubits:
raise ValueError("Input array does not represent a density matrix "
"with shape `(2 ** n, 2 ** n)` or `(2, ..., 2)`.")
# HACK: avoid circular import
from cirq.sim.density_matrix_utils import to_valid_density_matrix
# Do not enforce reshaping if the state all axes are dimension 2.
_ = to_valid_density_matrix(density_matrix_rep=state.reshape(dim, dim),
num_qubits=num_qubits,
dtype=state.dtype)
return sum(
p._expectation_from_density_matrix_no_validation(state, qubit_map)
for p in self)
