# StateFn¶

class StateFn(primitive=None, coeff=1.0, is_measurement=False)[source]

Bases: qiskit.aqua.operators.operator_base.OperatorBase

A class for representing state functions and measurements.

State functions are defined to be complex functions over a single binary string (as compared to an operator, which is defined as a function over two binary strings, or a function taking a binary function to another binary function). This function may be called by the eval() method.

Measurements are defined to be functionals over StateFns, taking them to real values. Generally, this real value is interpreted to represent the probability of some classical state (binary string) being observed from a probabilistic or quantum system represented by a StateFn. This leads to the equivalent definition, which is that a measurement m is a function over binary strings producing StateFns, such that the probability of measuring a given binary string b from a system with StateFn f is equal to the inner product between f and m(b).

NOTE: State functions here are not restricted to wave functions, as there is no requirement of normalization.

Parameters
• primitive (Union[str, dict, Result, list, ndarray, Statevector, QuantumCircuit, Instruction, OperatorBase, None]) -- The primitive which defines the behavior of the underlying State function.

• coeff (Union[int, float, complex, ParameterExpression]) -- A coefficient by which the state function is multiplied.

• is_measurement (bool) -- Whether the StateFn is a measurement operator

Methods

 add Return Operator addition of self and other, overloaded by +. adjoint Return a new Operator equal to the Operator's adjoint (conjugate transpose), overloaded by ~. assign_parameters Binds scalar values to any Terra Parameters in the coefficients or primitives of the Operator, or substitutes one Parameter for another. bind_parameters Same as assign_parameters, but maintained for consistency with QuantumCircuit in Terra (which has both assign_parameters and bind_parameters). compose Composition (Linear algebra-style: A@B(x) = A(B(x))) is not well defined for states in the binary function model, but is well defined for measurements. equals Evaluate Equality between Operators, overloaded by ==. eval Evaluate the Operator's underlying function, either on a binary string or another Operator. mul Returns the scalar multiplication of the Operator, overloaded by *, including support for Terra's Parameters, which can be bound to values later (via bind_parameters). neg Return the Operator's negation, effectively just multiplying by -1.0, overloaded by -. permute Permute the qubits of the state function. power Compose with Self Multiple Times, undefined for StateFns. primitive_strings Return a set of strings describing the primitives contained in the Operator. reduce Try collapsing the Operator structure, usually after some type of conversion, e.g. sample Sample the state function as a normalized probability distribution. tensor Return tensor product between self and other, overloaded by ^. tensorpower Return tensor product with self multiple times, overloaded by ^. to_density_matrix Return matrix representing product of StateFn evaluated on pairs of basis states. to_legacy_op Attempt to return the Legacy Operator representation of the Operator. to_matrix Return NumPy representation of the Operator. to_matrix_op Return a VectorStateFn for this StateFn. traverse Apply the convert_fn to the internal primitive if the primitive is an Operator (as in the case of OperatorStateFn).

Attributes

ENABLE_DEPRECATION = True
INDENTATION = ' '
coeff

A coefficient by which the state function is multiplied.

Return type

Union[int, float, complex, ParameterExpression]

is_measurement

Whether the StateFn object is a measurement Operator.

Return type

bool

num_qubits
Return type

int

parameters
primitive

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