squlearn.encoding_circuit.ChebyshevTower

class squlearn.encoding_circuit.ChebyshevTower(num_qubits: int, num_chebyshev: int, num_features: int = None, alpha: float = 1.0, num_layers: int = 1, rotation_gate: str = 'ry', hadamard_start: bool = True, arrangement: str = 'block', nonlinearity: str = 'arccos')

A feature-map that is based on the Chebyshev Tower encoding.

Example for 4 qubits, a 2 dimensional feature vector, 2 Chebyshev terms per feature, and 2 layers:

(Source code, png, hires.png, pdf)

../../_images/squlearn-encoding_circuit-ChebyshevTower-1.png

The encoding gate and the scaling factor can be adjusted by parameters. It is also possible to change the indexing of the features.

Parameters:

  • num_qubits (int) – Number of qubits of the ChebyshevTower encoding circuit

  • num_chebyshev (int) – Number of Chebyshev tower terms per feature dimension

  • num_features (int) – Dimension of the feature vector (default: None)

  • alpha (float) – Scaling factor of Chebyshev tower

  • num_layers (int) – Number of layers

  • rotation_gate (str) – Rotation gate to use. Either rx, ry or rz (default: ry)

  • hadamard_start (bool) – If true, the circuit starts with a layer of Hadamard gates (default: True)

  • arrangement (str) – Arrangement of the layers, either block or alternating. block: The features are stacked together, alternating: The features are placed alternately (default: block).

  • nonlinearity (str) – Mapping function to use for the feature encoding. Either arccos or arctan (default: arccos)

compose(x, concatenate_features=False, concatenate_parameters=False, num_circuit_features: Tuple[int, int] = (None, None))

Composition of encoding circuits with options for handling features and parameters

Number of qubits and features have to be equal in both encoding circuits! The special function and properties of the both encoding circuits are lost by this composition.

Parameters:

  • self (EncodingCircuitBase) – right / first encoding circuit

  • x (EncodingCircuitBase) – left / second encoding circuit

  • concatenate_features (bool) – If True, the features of both encoding circuits are concatenated (default: False). If False, the features of both encoding circuits are taken

  • concatenate_parameters (bool) – If True, the parameters of both encoding circuits are concatenated (default: False). If False, the parameters of both encoding circuits are taken

  • num_circuit_features (Tuple[int, int]) – Tuple of the number of features for both encoding circuits. This has to be provided if concatenate_features is True otherwise an error is raised.

Returns:

Returns the composed encoding circuit as special class ComposedEncodingCircuit

draw(output: str = None, num_features: int = None, feature_label: str = 'x', parameter_label: str = 'p', decompose: bool = False, **kwargs) → None

Draws the encoding circuit using the QuantumCircuit.draw() function.

Parameters:

  • output (str) – Output format of the drawing (default: None).

  • num_features (int) – Number of features to draw the circuit with (default: None).

  • feature_label (str) – Label for the feature vector (default:”x”).

  • parameter_label (str) – Label for the parameter vector (default:”p”).

  • decompose (bool) – If True, the circuit is decomposed before printing (default: False).

  • kwargs – Additional arguments from Qiskit’s QuantumCircuit.draw() function.

Raises:

ValueError – Raised if the number of features is not provided.

Returns:

Returns the circuit in qiskit QuantumCircuit.draw() format

generate_initial_parameters(num_features: int, seed: int | None = None) → ndarray

Generates random parameters for the encoding circuit

Parameters:

  • num_features (int) – Number of features of the input data

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

Returns:

The randomly generated parameters

get_circuit(features: ParameterVector | ndarray, parameters: ParameterVector | ndarray = None) → QuantumCircuit

Generates and returns the circuit of the Chebyshev encoding circuit.

Parameters:

  • features (Union[ParameterVector,np.ndarray]) – Input vector of the features from which the gate inputs are obtained

  • param_vec (Union[ParameterVector,np.ndarray]) – Input vector of the parameters from which the gate inputs are obtained

Returns:

Returns the circuit in Qiskit’s QuantumCircuit format

get_feature_bounds(num_features: int) → ndarray

Returns the feature bounds expanded for a given number of features.

Parameters:

num_features (int) – Number of features to expand the bounds for.

Returns:

Feature bounds expanded for the number of features.

Return type:

np.ndarray

get_params(deep: bool = True) → dict

Returns hyper-parameters and their values of the Chebyshev Tower encoding

Parameters:

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

Returns:

Dictionary with hyper-parameters and values.

inverse()

Returns the inverse of the encoding circuit.

Returns:

The inverse of the encoding circuit

set_params(**kwargs) → ChebyshevTower

Sets value of the encoding circuit hyper-parameters.

Parameters:

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