409 lines
17 KiB
Plaintext
409 lines
17 KiB
Plaintext
---
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title: ZZFeatureMap
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description: API reference for qiskit.circuit.library.ZZFeatureMap
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in_page_toc_min_heading_level: 1
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python_api_type: class
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python_api_name: qiskit.circuit.library.ZZFeatureMap
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---
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# ZZFeatureMap
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<Class id="qiskit.circuit.library.ZZFeatureMap" isDedicatedPage={true} github="https://github.com/Qiskit/qiskit/tree/stable/1.1/qiskit/circuit/library/data_preparation/zz_feature_map.py#L20-L114" signature="qiskit.circuit.library.ZZFeatureMap(feature_dimension, reps=2, entanglement='full', data_map_func=None, parameter_prefix='x', insert_barriers=False, name='ZZFeatureMap')" modifiers="class">
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Bases: [`PauliFeatureMap`](qiskit.circuit.library.PauliFeatureMap "qiskit.circuit.library.data_preparation.pauli_feature_map.PauliFeatureMap")
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Second-order Pauli-Z evolution circuit.
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For 3 qubits and 1 repetition and linear entanglement the circuit is represented by:
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```python
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┌───┐┌─────────────────┐
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┤ H ├┤ U1(2.0*φ(x[0])) ├──■────────────────────────────■────────────────────────────────────
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├───┤├─────────────────┤┌─┴─┐┌──────────────────────┐┌─┴─┐
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┤ H ├┤ U1(2.0*φ(x[1])) ├┤ X ├┤ U1(2.0*φ(x[0],x[1])) ├┤ X ├──■────────────────────────────■──
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├───┤├─────────────────┤└───┘└──────────────────────┘└───┘┌─┴─┐┌──────────────────────┐┌─┴─┐
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┤ H ├┤ U1(2.0*φ(x[2])) ├──────────────────────────────────┤ X ├┤ U1(2.0*φ(x[1],x[2])) ├┤ X ├
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└───┘└─────────────────┘ └───┘└──────────────────────┘└───┘
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```
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where $\varphi$ is a classical non-linear function, which defaults to $\varphi(x) = x$ if and $\varphi(x,y) = (\pi - x)(\pi - y)$.
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**Examples**
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```python
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>>> from qiskit.circuit.library import ZZFeatureMap
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>>> prep = ZZFeatureMap(2, reps=1)
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>>> print(prep)
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┌───┐┌──────────────┐
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q_0: ┤ H ├┤ U1(2.0*x[0]) ├──■───────────────────────────────────────■──
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├───┤├──────────────┤┌─┴─┐┌─────────────────────────────────┐┌─┴─┐
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q_1: ┤ H ├┤ U1(2.0*x[1]) ├┤ X ├┤ U1(2.0*(pi - x[0])*(pi - x[1])) ├┤ X ├
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└───┘└──────────────┘└───┘└─────────────────────────────────┘└───┘
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```
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```python
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>>> from qiskit.circuit.library import EfficientSU2
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>>> classifier = ZZFeatureMap(3) + EfficientSU2(3)
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>>> classifier.num_parameters
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15
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>>> classifier.parameters # 'x' for the data preparation, 'θ' for the SU2 parameters
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ParameterView([
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ParameterVectorElement(x[0]), ParameterVectorElement(x[1]),
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ParameterVectorElement(x[2]), ParameterVectorElement(θ[0]),
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ParameterVectorElement(θ[1]), ParameterVectorElement(θ[2]),
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ParameterVectorElement(θ[3]), ParameterVectorElement(θ[4]),
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ParameterVectorElement(θ[5]), ParameterVectorElement(θ[6]),
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ParameterVectorElement(θ[7]), ParameterVectorElement(θ[8]),
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ParameterVectorElement(θ[9]), ParameterVectorElement(θ[10]),
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ParameterVectorElement(θ[11]), ParameterVectorElement(θ[12]),
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ParameterVectorElement(θ[13]), ParameterVectorElement(θ[14]),
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ParameterVectorElement(θ[15]), ParameterVectorElement(θ[16]),
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ParameterVectorElement(θ[17]), ParameterVectorElement(θ[18]),
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ParameterVectorElement(θ[19]), ParameterVectorElement(θ[20]),
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ParameterVectorElement(θ[21]), ParameterVectorElement(θ[22]),
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ParameterVectorElement(θ[23])
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])
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>>> classifier.count_ops()
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OrderedDict([('ZZFeatureMap', 1), ('EfficientSU2', 1)])
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```
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Create a new second-order Pauli-Z expansion.
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**Parameters**
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* **feature\_dimension** ([*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")) – Number of features.
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* **reps** ([*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")) – The number of repeated circuits, has a min. value of 1.
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* **entanglement** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)") *|*[*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")*]] |* [*Callable*](https://docs.python.org/3/library/typing.html#typing.Callable "(in Python v3.12)")*\[\[*[*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")*],* [*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")*]]*) – Specifies the entanglement structure. Refer to [`NLocal`](qiskit.circuit.library.NLocal "qiskit.circuit.library.NLocal") for detail.
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* **data\_map\_func** ([*Callable*](https://docs.python.org/3/library/typing.html#typing.Callable "(in Python v3.12)")*\[\[*[*ndarray*](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.html#numpy.ndarray "(in NumPy v2.0)")*],* [*float*](https://docs.python.org/3/library/functions.html#float "(in Python v3.12)")*] | None*) – A mapping function for data x.
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* **parameter\_prefix** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")) – The prefix used if default parameters are generated.
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* **insert\_barriers** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) – If True, barriers are inserted in between the evolution instructions and hadamard layers.
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**Raises**
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[**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError "(in Python v3.12)") – If the feature dimension is smaller than 2.
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## Attributes
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### alpha
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.alpha">
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The Pauli rotation factor (alpha).
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**Returns**
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The Pauli rotation factor.
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</Attribute>
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### ancillas
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.ancillas">
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A list of `AncillaQubit`s in the order that they were added. You should not mutate this.
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</Attribute>
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### calibrations
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.calibrations">
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Return calibration dictionary.
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The custom pulse definition of a given gate is of the form `{'gate_name': {(qubits, params): schedule}}`
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</Attribute>
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### clbits
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.clbits">
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A list of `Clbit`s in the order that they were added. You should not mutate this.
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</Attribute>
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### data
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.data" />
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### entanglement
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.entanglement">
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Get the entanglement strategy.
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**Returns**
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The entanglement strategy, see `get_entangler_map()` for more detail on how the format is interpreted.
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</Attribute>
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### entanglement\_blocks
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.entanglement_blocks" />
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### feature\_dimension
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.feature_dimension">
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Returns the feature dimension (which is equal to the number of qubits).
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**Returns**
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The feature dimension of this feature map.
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</Attribute>
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### flatten
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.flatten">
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Returns whether the circuit is wrapped in nested gates/instructions or flattened.
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</Attribute>
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### global\_phase
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.global_phase">
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The global phase of the current circuit scope in radians.
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</Attribute>
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### initial\_state
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.initial_state">
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Return the initial state that is added in front of the n-local circuit.
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**Returns**
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The initial state.
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</Attribute>
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### insert\_barriers
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.insert_barriers">
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If barriers are inserted in between the layers or not.
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**Returns**
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`True`, if barriers are inserted in between the layers, `False` if not.
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</Attribute>
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### instances
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.instances" attributeValue="164" />
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### layout
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.layout">
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Return any associated layout information about the circuit
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This attribute contains an optional [`TranspileLayout`](qiskit.transpiler.TranspileLayout "qiskit.transpiler.TranspileLayout") object. This is typically set on the output from [`transpile()`](compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") or [`PassManager.run()`](qiskit.transpiler.PassManager#run "qiskit.transpiler.PassManager.run") to retain information about the permutations caused on the input circuit by transpilation.
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There are two types of permutations caused by the [`transpile()`](compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") function, an initial layout which permutes the qubits based on the selected physical qubits on the [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target"), and a final layout which is an output permutation caused by [`SwapGate`](qiskit.circuit.library.SwapGate "qiskit.circuit.library.SwapGate")s inserted during routing.
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</Attribute>
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### metadata
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.metadata">
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Arbitrary user-defined metadata for the circuit.
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Qiskit will not examine the content of this mapping, but it will pass it through the transpiler and reattach it to the output, so you can track your own metadata.
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</Attribute>
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### num\_ancillas
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_ancillas">
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Return the number of ancilla qubits.
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</Attribute>
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### num\_captured\_vars
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_captured_vars">
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The number of real-time classical variables in the circuit marked as captured from an enclosing scope.
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This is the length of the `iter_captured_vars()` iterable. If this is non-zero, [`num_input_vars`](#qiskit.circuit.library.ZZFeatureMap.num_input_vars "qiskit.circuit.library.ZZFeatureMap.num_input_vars") must be zero.
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</Attribute>
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### num\_clbits
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_clbits">
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Return number of classical bits.
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</Attribute>
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### num\_declared\_vars
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_declared_vars">
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The number of real-time classical variables in the circuit that are declared by this circuit scope, excluding inputs or captures.
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This is the length of the `iter_declared_vars()` iterable.
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</Attribute>
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### num\_input\_vars
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_input_vars">
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The number of real-time classical variables in the circuit marked as circuit inputs.
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This is the length of the `iter_input_vars()` iterable. If this is non-zero, [`num_captured_vars`](#qiskit.circuit.library.ZZFeatureMap.num_captured_vars "qiskit.circuit.library.ZZFeatureMap.num_captured_vars") must be zero.
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</Attribute>
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### num\_layers
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_layers">
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Return the number of layers in the n-local circuit.
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**Returns**
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The number of layers in the circuit.
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</Attribute>
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### num\_parameters
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_parameters" />
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### num\_parameters\_settable
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_parameters_settable">
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The number of distinct parameters.
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</Attribute>
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### num\_qubits
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_qubits">
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Returns the number of qubits in this circuit.
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**Returns**
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The number of qubits.
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</Attribute>
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### num\_vars
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.num_vars">
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The number of real-time classical variables in the circuit.
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This is the length of the `iter_vars()` iterable.
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</Attribute>
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### op\_start\_times
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.op_start_times">
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Return a list of operation start times.
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This attribute is enabled once one of scheduling analysis passes runs on the quantum circuit.
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**Returns**
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List of integers representing instruction start times. The index corresponds to the index of instruction in `QuantumCircuit.data`.
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**Raises**
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[**AttributeError**](https://docs.python.org/3/library/exceptions.html#AttributeError "(in Python v3.12)") – When circuit is not scheduled.
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</Attribute>
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### ordered\_parameters
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.ordered_parameters">
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The parameters used in the underlying circuit.
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This includes float values and duplicates.
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**Examples**
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```python
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>>> # prepare circuit ...
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>>> print(nlocal)
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┌───────┐┌──────────┐┌──────────┐┌──────────┐
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q_0: ┤ Ry(1) ├┤ Ry(θ[1]) ├┤ Ry(θ[1]) ├┤ Ry(θ[3]) ├
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└───────┘└──────────┘└──────────┘└──────────┘
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>>> nlocal.parameters
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{Parameter(θ[1]), Parameter(θ[3])}
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>>> nlocal.ordered_parameters
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[1, Parameter(θ[1]), Parameter(θ[1]), Parameter(θ[3])]
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```
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**Returns**
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The parameters objects used in the circuit.
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</Attribute>
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### parameter\_bounds
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.parameter_bounds">
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The parameter bounds for the unbound parameters in the circuit.
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**Returns**
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A list of pairs indicating the bounds, as (lower, upper). None indicates an unbounded parameter in the corresponding direction. If `None` is returned, problem is fully unbounded.
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</Attribute>
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### parameters
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.parameters" />
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### paulis
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.paulis">
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The Pauli strings used in the entanglement of the qubits.
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**Returns**
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The Pauli strings as list.
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</Attribute>
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### preferred\_init\_points
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.preferred_init_points">
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The initial points for the parameters. Can be stored as initial guess in optimization.
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**Returns**
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The initial values for the parameters, or None, if none have been set.
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</Attribute>
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### prefix
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.prefix" attributeValue="'circuit'" />
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### qregs
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.qregs" attributeTypeHint="list[QuantumRegister]">
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A list of the `QuantumRegister`s in this circuit. You should not mutate this.
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</Attribute>
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### qubits
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.qubits">
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A list of `Qubit`s in the order that they were added. You should not mutate this.
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</Attribute>
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### reps
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.reps">
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The number of times rotation and entanglement block are repeated.
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**Returns**
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The number of repetitions.
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</Attribute>
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### rotation\_blocks
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.rotation_blocks">
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The blocks in the rotation layers.
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**Returns**
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The blocks in the rotation layers.
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</Attribute>
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### name
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.name" attributeTypeHint="str">
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A human-readable name for the circuit.
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</Attribute>
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### cregs
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.cregs" attributeTypeHint="list[ClassicalRegister]">
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A list of the `ClassicalRegister`s in this circuit. You should not mutate this.
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</Attribute>
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### duration
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.duration" attributeTypeHint="int | float | None">
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The total duration of the circuit, set by a scheduling transpiler pass. Its unit is specified by [`unit`](#qiskit.circuit.library.ZZFeatureMap.unit "qiskit.circuit.library.ZZFeatureMap.unit").
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</Attribute>
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### unit
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<Attribute id="qiskit.circuit.library.ZZFeatureMap.unit">
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The unit that [`duration`](#qiskit.circuit.library.ZZFeatureMap.duration "qiskit.circuit.library.ZZFeatureMap.duration") is specified in.
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</Attribute>
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</Class>
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