squlearn.observables.observable_base.ObservableBase

class squlearn.observables.observable_base.ObservableBase(num_qubits: int)

Base class for observables.

Parameters:

num_qubits (int) – Number of qubits.

Attributes:

num_parameters

Number of trainable parameters in the observable.

Type:

int

num_qubits

Number of qubits in the observable.

Type:

int

Methods:

generate_initial_parameters(ones: bool = True, seed: int | None = None) → ndarray

Generates random parameters for the observable

Parameters:

• ones (bool) – If True, returns an array of ones (default: True)

• seed (Union[int,None]) – Seed for the random number generator

Returns:

The randomly generated parameters

get_operator(parameters: ParameterVector | ndarray) → SparsePauliOp

Returns Operator as a SparsePauliOp expression.

Parameters:

parameters (Union[ParameterVector, np.ndarray]) – Vector of parameters used in the operator

Returns:

StateFn expression of the observable.

get_params(deep: bool = True) → dict

Returns hyper-parameters and their values of the operator.

Parameters:

deep (bool) – If True, also the parameters for contained objects are returned (default=True).

Returns:

Dictionary with hyper-parameters and values.

abstract get_pauli(parameters: ParameterVector | ndarray) → SparsePauliOp

Returns the PauliOp expression of the observable.

Parameters:

parameters (Union[ParameterVector, np.ndarray]) – Vector of parameters used in the operator

Returns:

Expectation operator in Qiskit’s PauliOp class

get_pauli_mapped(parameters: ParameterVector | ndarray) → SparsePauliOp

Changes the operator to the physical qubits, set by set_map().

Parameters:

parameters (Union[ParameterVector, np.ndarray]) – Vector of parameters used in the operator

Returns:

Expectation operator in Qiskit’s SprasePauliOp class with qubits mapped to physical ones

set_map(qubit_map: list | dict, num_all_qubits: int)

Function for setting a qubit mapping from physical qubits to the ones of the operator.

This function is necessary whenever the number of physical qubits are different from the operator definition, as for example when running on a real backend. The number of qubits in the system has to be larger than the number of qubits in the observable.

Parameters:

• qubit_map (Union[list, dict]) – A list or dictionary specifying which of the input qubits are mapped to the output qubits.

• num_all_qubits (int) – The total number of qubits in the system.

set_params(**params) → None

Sets value of the operator hyper-parameters.

Parameters:

params – Hyper-parameters and their values, e.g. num_qubits=2.