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OperatorStateFn

OperatorStateFn(primitive, coeff=1.0, is_measurement=False)

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Bases: qiskit.opflow.state_fns.state_fn.StateFn

A class for state functions and measurements which are defined by a density Operator, stored using an OperatorBase.

Parameters

  • primitive (OperatorBase) – The OperatorBase which defines the behavior of the underlying State function.
  • coeff (Union[complex, ParameterExpression]) – A coefficient by which to multiply the state function
  • is_measurement (bool) – Whether the StateFn is a measurement operator

Methods Defined Here

add

OperatorStateFn.add(other)

Return Operator addition of self and other, overloaded by +.

Parameters

other (OperatorBase) – An OperatorBase with the same number of qubits as self, and in the same ‘Operator’, ‘State function’, or ‘Measurement’ category as self (i.e. the same type of underlying function).

Return type

Union[OperatorStateFn, SummedOp]

Returns

An OperatorBase equivalent to the sum of self and other.

adjoint

OperatorStateFn.adjoint()

Return a new Operator equal to the Operator’s adjoint (conjugate transpose), overloaded by ~. For StateFns, this also turns the StateFn into a measurement.

Return type

OperatorStateFn

Returns

An OperatorBase equivalent to the adjoint of self.

eval

OperatorStateFn.eval(front=None)

Evaluate the Operator’s underlying function, either on a binary string or another Operator. A square binary Operator can be defined as a function taking a binary function to another binary function. This method returns the value of that function for a given StateFn or binary string. For example, op.eval('0110').eval('1110') can be seen as querying the Operator’s matrix representation by row 6 and column 14, and will return the complex value at those “indices.” Similarly for a StateFn, op.eval('1011') will return the complex value at row 11 of the vector representation of the StateFn, as all StateFns are defined to be evaluated from Zero implicitly (i.e. it is as if .eval('0000') is already called implicitly to always “indexing” from column 0).

If front is None, the matrix-representation of the operator is returned.

Parameters

front (Union[str, dict, ndarray, OperatorBase, Statevector, None]) – The bitstring, dict of bitstrings (with values being coefficients), or StateFn to evaluated by the Operator’s underlying function, or None.

Return type

Union[OperatorBase, complex]

Returns

The output of the Operator’s evaluation function. If self is a StateFn, the result is a float or complex. If self is an Operator (PrimitiveOp, ComposedOp, SummedOp, EvolvedOp, etc.), the result is a StateFn. If front is None, the matrix-representation of the operator is returned, which is a MatrixOp for the operators and a VectorStateFn for state-functions. If either self or front contain proper ListOps (not ListOp subclasses), the result is an n-dimensional list of complex or StateFn results, resulting from the recursive evaluation by each OperatorBase in the ListOps.

permute

OperatorStateFn.permute(permutation)

Permute the qubits of the state function.

Parameters

permutation (List[int]) – A list defining where each qubit should be permuted. The qubit at index j of the circuit should be permuted to position permutation[j].

Return type

OperatorStateFn

Returns

A new StateFn containing the permuted primitive.

primitive_strings

OperatorStateFn.primitive_strings()

Return a set of strings describing the primitives contained in the Operator. For example, {'QuantumCircuit', 'Pauli'}. For hierarchical Operators, such as ListOps, this can help illuminate the primitives represented in the various recursive levels, and therefore which conversions can be applied.

Return type

Set[str]

Returns

A set of strings describing the primitives contained within the Operator.

sample

OperatorStateFn.sample(shots=1024, massive=False, reverse_endianness=False)

Sample the state function as a normalized probability distribution. Returns dict of bitstrings in order of probability, with values being probability.

Parameters

  • shots (int) – The number of samples to take to approximate the State function.
  • massive (bool) – Whether to allow large conversions, e.g. creating a matrix representing over 16 qubits.
  • reverse_endianness (bool) – Whether to reverse the endianness of the bitstrings in the return dict to match Terra’s big-endianness.

Returns

A dict containing pairs sampled strings from the State function and sampling frequency divided by shots.

tensor

OperatorStateFn.tensor(other)

Return tensor product between self and other, overloaded by ^. Note: You must be conscious of Qiskit’s big-endian bit printing convention. Meaning, Plus.tensor(Zero) produces a |+⟩ on qubit 0 and a |0⟩ on qubit 1, or |+⟩⨂|0⟩, but would produce a QuantumCircuit like

|0⟩– |+⟩–

Because Terra prints circuits and results with qubit 0 at the end of the string or circuit.

Parameters

other (OperatorBase) – The OperatorBase to tensor product with self.

Return type

Union[OperatorStateFn, TensoredOp]

Returns

An OperatorBase equivalent to the tensor product of self and other.

to_circuit_op

OperatorStateFn.to_circuit_op()

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.

to_density_matrix

OperatorStateFn.to_density_matrix(massive=False)

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.

Return type

ndarray

to_matrix

OperatorStateFn.to_matrix(massive=False)

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.

Parameters

massive (bool) – Whether to allow large conversions, e.g. creating a matrix representing over 16 qubits.

Returns

Vector of state vector

Return type

np.ndarray

Raises

ValueError – Invalid parameters.

to_matrix_op

OperatorStateFn.to_matrix_op(massive=False)

Return a MatrixOp for this operator.

Return type

OperatorStateFn


Attributes

INDENTATION

= '  '

coeff

A coefficient by which the state function is multiplied.

Return type

Union[complex, ParameterExpression]

instance_id

Return the unique instance id.

Return type

int

is_measurement

Whether the StateFn object is a measurement Operator.

Return type

bool

num_qubits

Return type

int

parameters

primitive

qiskit.opflow.operator_base.OperatorBase

The primitive which defines the behavior of the underlying State function.

settings

Return settings.

Return type

Dict

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