63 lines
2.7 KiB
Plaintext
63 lines
2.7 KiB
Plaintext
---
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title: QFI
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description: API reference for qiskit.opflow.gradients.QFI
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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.opflow.gradients.QFI
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---
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# QFI
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<Class id="qiskit.opflow.gradients.QFI" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.45/qiskit/opflow/gradients/qfi.py" signature="qiskit.opflow.gradients.QFI(qfi_method='lin_comb_full')" modifiers="class">
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Bases: [`QFIBase`](qiskit.opflow.gradients.QFIBase "qiskit.opflow.gradients.qfi_base.QFIBase")
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Deprecated: Compute the Quantum Fisher Information (QFI).
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Computes the QFI given a pure, parameterized quantum state, where QFI is:
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$$
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\mathrm{QFI}_{kl}= 4 \mathrm{Re}[\langle \partial_k \psi | \partial_l \psi \rangle
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− \langle\partial_k \psi | \psi \rangle \langle\psi | \partial_l \psi \rangle].
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$$
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<Admonition title="Deprecated since version 0.24.0" type="danger">
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The class `qiskit.opflow.gradients.qfi.QFI` is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. For code migration guidelines, visit [https://qisk.it/opflow\_migration](https://qisk.it/opflow_migration).
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</Admonition>
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## Attributes
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### qfi\_method
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<Attribute id="qiskit.opflow.gradients.QFI.qfi_method">
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Returns `CircuitQFI`.
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**Returns**
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`CircuitQFI`.
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</Attribute>
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## Methods
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### convert
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<Function id="qiskit.opflow.gradients.QFI.convert" signature="convert(operator, params=None)">
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**Parameters**
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* **operator** ([*CircuitStateFn*](qiskit.opflow.state_fns.CircuitStateFn "qiskit.opflow.state_fns.circuit_state_fn.CircuitStateFn")) – The operator corresponding to the quantum state |ψ(ω)〉for which we compute the QFI
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* **params** ([*ParameterVector*](qiskit.circuit.ParameterVector "qiskit.circuit.parametervector.ParameterVector") *|*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression") *|*[*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*] | None*) – The parameters we are computing the QFI wrt: ω If not explicitly passed, they are inferred from the operator and sorted by name.
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**Returns**
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ListOp\[ListOp] where the operator at position k,l corresponds to QFI\_kl
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**Raises**
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[**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError "(in Python v3.12)") – If operator is not parameterized.
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**Return type**
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[*ListOp*](qiskit.opflow.list_ops.ListOp "qiskit.opflow.list_ops.list_op.ListOp")
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</Function>
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</Class>
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