--- title: ZZFeatureMap (v2.3) description: API reference for qiskit.circuit.library.ZZFeatureMap in qiskit v2.3 source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/2.3/qiskit.circuit.library.ZZFeatureMap --- # ZZFeatureMap *class* `qiskit.circuit.library.ZZFeatureMap(feature_dimension, reps=2, entanglement='full', data_map_func=None, parameter_prefix='x', insert_barriers=False, name='ZZFeatureMap')` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.3/qiskit/circuit/library/data_preparation/_zz_feature_map.py#L21-L152) Bases: [`PauliFeatureMap`](/docs/api/qiskit/2.3/qiskit.circuit.library.PauliFeatureMap "qiskit.circuit.library.data_preparation.pauli_feature_map.PauliFeatureMap") Second-order Pauli-Z evolution circuit. For 3 qubits and 1 repetition and linear entanglement the circuit is represented by: ```text ┌───┐┌────────────────┐ ┤ H ├┤ P(2.0*φ(x[0])) ├──■───────────────────────────■─────────────────────────────────── ├───┤├────────────────┤┌─┴─┐┌─────────────────────┐┌─┴─┐ ┤ H ├┤ P(2.0*φ(x[1])) ├┤ X ├┤ P(2.0*φ(x[0],x[1])) ├┤ X ├──■───────────────────────────■── ├───┤├────────────────┤└───┘└─────────────────────┘└───┘┌─┴─┐┌─────────────────────┐┌─┴─┐ ┤ H ├┤ P(2.0*φ(x[2])) ├─────────────────────────────────┤ X ├┤ P(2.0*φ(x[1],x[2])) ├┤ X ├ └───┘└────────────────┘ └───┘└─────────────────────┘└───┘ ``` Here, $\varphi$ is a classical non-linear function, which defaults to $\varphi(x) = x$ if $|S| = 1$ and $\varphi(x,y) = (\pi - x)(\pi - y)$ if $|S| > 1$, and $S$ is the set of qubit indices describing the connections in the feature map. See the docstring of `pauli_feature_map()` for more detail. Examples: ```python from qiskit.circuit.library import ZZFeatureMap prep = ZZFeatureMap(2, reps=1) print(prep.decompose()) ``` ```text ┌───┐┌─────────────┐ q_0: ┤ H ├┤ P(2.0*x[0]) ├──■──────────────────────────────────────■── ├───┤├─────────────┤┌─┴─┐┌────────────────────────────────┐┌─┴─┐ q_1: ┤ H ├┤ P(2.0*x[1]) ├┤ X ├┤ P(2.0*(pi - x[0])*(pi - x[1])) ├┤ X ├ └───┘└─────────────┘└───┘└────────────────────────────────┘└───┘ ``` ```python from qiskit.circuit.library import EfficientSU2 classifier = ZZFeatureMap(3).compose(EfficientSU2(3)) classifier.num_parameters ``` ```text 27 ``` ```python classifier.parameters # 'x' for the data preparation, 'θ' for the SU2 parameters ``` ```text ParameterView([ ParameterVectorElement(x[0]), ParameterVectorElement(x[1]), ParameterVectorElement(x[2]), ParameterVectorElement(θ[0]), ParameterVectorElement(θ[1]), ParameterVectorElement(θ[2]), ParameterVectorElement(θ[3]), ParameterVectorElement(θ[4]), ParameterVectorElement(θ[5]), ParameterVectorElement(θ[6]), ParameterVectorElement(θ[7]), ParameterVectorElement(θ[8]), ParameterVectorElement(θ[9]), ParameterVectorElement(θ[10]), ParameterVectorElement(θ[11]), ParameterVectorElement(θ[12]), ParameterVectorElement(θ[13]), ParameterVectorElement(θ[14]), ParameterVectorElement(θ[15]), ParameterVectorElement(θ[16]), ParameterVectorElement(θ[17]), ParameterVectorElement(θ[18]), ParameterVectorElement(θ[19]), ParameterVectorElement(θ[20]), ParameterVectorElement(θ[21]), ParameterVectorElement(θ[22]), ParameterVectorElement(θ[23]) ]) ``` ```python classifier.count_ops() ``` ```text OrderedDict([('ZZFeatureMap', 1), ('EfficientSU2', 1)]) ``` > **Deprecated since version 2.1** > > The class `qiskit.circuit.library.data_preparation._zz_feature_map.ZZFeatureMap` is deprecated as of Qiskit 2.1. It will be removed in Qiskit 3.0. Use the zz\_feature\_map function as a replacement. Note that this will no longer return a BlueprintCircuit, but just a plain QuantumCircuit. **Parameters** - **feature\_dimension** ([*int*](https://docs.python.org/3/library/functions.html#int)) – Number of features. - **reps** ([*int*](https://docs.python.org/3/library/functions.html#int)) – The number of repeated circuits, has a min. value of 1. - **entanglement** ([*str*](https://docs.python.org/3/library/stdtypes.html#str) *|*[*Dict*](https://docs.python.org/3/library/typing.html#typing.Dict)*\[*[*int*](https://docs.python.org/3/library/functions.html#int)*,* [*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*Tuple*](https://docs.python.org/3/library/typing.html#typing.Tuple)*\[*[*int*](https://docs.python.org/3/library/functions.html#int)*]]] |* [*Callable*](https://docs.python.org/3/library/typing.html#typing.Callable)*\[\[*[*int*](https://docs.python.org/3/library/functions.html#int)*],* [*str*](https://docs.python.org/3/library/stdtypes.html#str) *|*[*Dict*](https://docs.python.org/3/library/typing.html#typing.Dict)*\[*[*int*](https://docs.python.org/3/library/functions.html#int)*,* [*List*](https://docs.python.org/3/library/typing.html#typing.List)*\[*[*Tuple*](https://docs.python.org/3/library/typing.html#typing.Tuple)*\[*[*int*](https://docs.python.org/3/library/functions.html#int)*]]]]*) – Specifies the entanglement structure. Refer to [`PauliFeatureMap`](/docs/api/qiskit/2.3/qiskit.circuit.library.PauliFeatureMap "qiskit.circuit.library.PauliFeatureMap") for detail. - **data\_map\_func** ([*Callable*](https://docs.python.org/3/library/typing.html#typing.Callable)*\[\[*[*ndarray*](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.html#numpy.ndarray)*],* [*float*](https://docs.python.org/3/library/functions.html#float)*] | None*) – A mapping function for the data `x`. - **parameter\_prefix** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – The prefix used if default parameters are generated. - **insert\_barriers** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – If `True`, barriers are inserted in between the evolution instructions and hadamard layers. - **name** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – **Raises** [**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError) – If the feature dimension is smaller than 2. ## Attributes ### name Type: `str` A human-readable name for the circuit. **Example** ```python from qiskit import QuantumCircuit qc = QuantumCircuit(2, 2, name="my_circuit") print(qc.name) ``` ```text my_circuit ```