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StateFn

qiskit.opflow.state_fns.StateFn(primitive=None, coeff=1.0, is_measurement=False) GitHub(opens in a new tab)

Bases: OperatorBase

Deprecated: 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.

Deprecated since version 0.24.0

The class qiskit.opflow.state_fns.state_fn.StateFn is deprecated as of qiskit-terra 0.24.0. It will be removed in the Qiskit 1.0 release. For code migration guidelines, visit https://qisk.it/opflow_migration(opens in a new tab).

Parameters

Return type

StateFn


Attributes

INDENTATION

= '  '

coeff

A coefficient by which the state function is multiplied.

instance_id

Return the unique instance id.

is_measurement

Whether the StateFn object is a measurement Operator.

num_qubits

parameters

primitive

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

settings

Return settings.


Methods

add

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).

Returns

An OperatorBase equivalent to the sum of self and other.

Return type

OperatorBase

adjoint

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.

Returns

An OperatorBase equivalent to the adjoint of self.

Return type

OperatorBase

assign_parameters

assign_parameters(param_dict)

Binds scalar values to any Terra Parameters in the coefficients or primitives of the Operator, or substitutes one Parameter for another. This method differs from Terra’s assign_parameters in that it also supports lists of values to assign for a give Parameter, in which case self will be copied for each parameterization in the binding list(s), and all the copies will be returned in an OpList. If lists of parameterizations are used, every Parameter in the param_dict must have the same length list of parameterizations.

Parameters

param_dict (dict(opens in a new tab)) – The dictionary of Parameters to replace, and values or lists of values by which to replace them.

Returns

The OperatorBase with the Parameters in self replaced by the values or Parameters in param_dict. If param_dict contains parameterization lists, this OperatorBase is an OpList.

Return type

OperatorBase

compose

compose(other, permutation=None, front=False)

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.

Parameters

Returns

An Operator equivalent to the function composition of self and other.

Raises

ValueError(opens in a new tab) – If self is not a measurement, it cannot be composed from the right.

Return type

OperatorBase

equals

equals(other)

Evaluate Equality between Operators, overloaded by ==. Only returns True if self and other are of the same representation (e.g. a DictStateFn and CircuitStateFn will never be equal, even if their vector representations are equal), their underlying primitives are equal (this means for ListOps, OperatorStateFns, or EvolvedOps the equality is evaluated recursively downwards), and their coefficients are equal.

Parameters

other (OperatorBase) – The OperatorBase to compare to self.

Returns

A bool equal to the equality of self and other.

Return type

bool(opens in a new tab)

eval

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 (str(opens in a new tab) |Dict(opens in a new tab)[str(opens in a new tab), complex(opens in a new tab)] | ndarray(opens in a new tab) |OperatorBase |Statevector | None) – The bitstring, dict of bitstrings (with values being coefficients), or StateFn to evaluated by the Operator’s underlying function, or None.

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.

Return type

OperatorBase | complex(opens in a new tab)

mul

mul(scalar)

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).

Parameters

scalar (complex(opens in a new tab) |ParameterExpression) – The real or complex scalar by which to multiply the Operator, or the ParameterExpression to serve as a placeholder for a scalar factor.

Returns

An OperatorBase equivalent to product of self and scalar.

Return type

OperatorBase

permute

permute(permutation)

Permute the qubits of the state function.

Parameters

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

Returns

A new StateFn containing the permuted primitive.

Return type

OperatorBase

power

power(exponent)

Compose with Self Multiple Times, undefined for StateFns.

Parameters

exponent (int(opens in a new tab)) – The number of times to compose self with self.

Raises

ValueError(opens in a new tab) – This function is not defined for StateFns.

Return type

OperatorBase

primitive_strings

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.

Returns

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

Return type

Set(opens in a new tab)[str(opens in a new tab)]

reduce

reduce()

Try collapsing the Operator structure, usually after some type of conversion, e.g. trying to add Operators in a SummedOp or delete needless IGates in a CircuitOp. If no reduction is available, just returns self.

Returns

The reduced OperatorBase.

Return type

OperatorBase

sample

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(opens in a new tab)) – The number of samples to take to approximate the State function.
  • massive (bool(opens in a new tab)) – Whether to allow large conversions, e.g. creating a matrix representing over 16 qubits.
  • reverse_endianness (bool(opens in a new tab)) – 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.

Return type

Dict(opens in a new tab)[str(opens in a new tab), float(opens in a new tab)]

tensor

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.

Returns

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

Return type

OperatorBase

tensorpower

tensorpower(other)

Return tensor product with self multiple times, overloaded by ^.

Parameters

other (int(opens in a new tab)) – The int number of times to tensor product self with itself via tensorpower.

Returns

An OperatorBase equivalent to the tensorpower of self by other.

Return type

OperatorBase | int(opens in a new tab)

to_circuit_op

to_circuit_op()

Returns a CircuitOp equivalent to this Operator.

Return type

OperatorBase

to_density_matrix

to_density_matrix(massive=False)

Return matrix representing product of StateFn evaluated on pairs of basis states. Overridden by child classes.

Parameters

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

Returns

The NumPy array representing the density matrix of the State function.

Raises

ValueError(opens in a new tab) – If massive is set to False, and exponentially large computation is needed.

Return type

ndarray(opens in a new tab)

to_matrix

to_matrix(massive=False)

Return NumPy representation of the Operator. Represents the evaluation of the Operator’s underlying function on every combination of basis binary strings. Warn if more than 16 qubits to force having to set massive=True if such a large vector is desired.

Returns

The NumPy ndarray equivalent to this Operator.

Return type

ndarray(opens in a new tab)

to_matrix_op

to_matrix_op(massive=False)

Return a VectorStateFn for this StateFn.

Parameters

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

Returns

A VectorStateFn equivalent to self.

Return type

OperatorBase

traverse

traverse(convert_fn, coeff=None)

Apply the convert_fn to the internal primitive if the primitive is an Operator (as in the case of OperatorStateFn). Otherwise do nothing. Used by converters.

Parameters

Returns

The converted StateFn.

Return type

OperatorBase

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