squlearn.encoding_circuit
.ChebyshevTower
- class squlearn.encoding_circuit.ChebyshevTower(num_qubits: int, num_features: int, num_chebyshev: int, 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
)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_features (int) – Dimension of the feature vector
n_chebyshev (int) – Number of Chebyshev tower terms per feature dimension
alpha (float) – Scaling factor of Chebyshev tower
num_layers (int) – Number of layers
rotation_gate (str) – Rotation gate to use. Either
rx
,ry
orrz
(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
oralternating
.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
orarctan
(default:arccos
)
- draw(output: str = None, feature_label: str = 'x', parameter_label: str = 'p', decompose: bool = False, **kwargs) None
Draws the encoding circuit circuit using the QuantumCircuit.draw() function.
- Parameters:
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.
- Returns:
Returns the circuit in qiskit QuantumCircuit.draw() format
- generate_initial_parameters(seed: int | None = None) ndarray
Generates random parameters for the encoding circuit
- Parameters:
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_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.
- set_params(**kwargs) ChebyshevTower
Sets value of the encoding circuit hyper-parameters.
- Parameters:
params – Hyper-parameters and their values, e.g.
num_qubits=2
.