72 lines
3.0 KiB
Plaintext
72 lines
3.0 KiB
Plaintext
---
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title: QFI
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description: API reference for qiskit.algorithms.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.algorithms.gradients.QFI
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---
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# QFI
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<Class id="qiskit.algorithms.gradients.QFI" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.23/qiskit/algorithms/gradients/qfi.py" signature="QFI(qgt, options=None)" modifiers="class">
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Bases: `abc.ABC`
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Computes the Quantum Fisher Information (QFI) given a pure, parameterized quantum state. QFI is defined as:
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$$
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\mathrm{QFI}_{ij}= 4 \mathrm{Re}[\langle \partial_i \psi | \partial_j \psi \rangle
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- \langle\partial_i \psi | \psi \rangle \langle\psi | \partial_j \psi \rangle].
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$$
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**Parameters**
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* **qgt** ([*BaseQGT*](qiskit.algorithms.gradients.BaseQGT "qiskit.algorithms.gradients.BaseQGT")) – The quantum geometric tensor used to compute the QFI.
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* **options** ([*Options*](qiskit.providers.Options "qiskit.providers.Options") *| None*) – Backend runtime options used for circuit execution. The order of priority is: options in `run` method > QFI’s default options > primitive’s default setting. Higher priority setting overrides lower priority setting.
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## Methods
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### run
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<Function id="qiskit.algorithms.gradients.QFI.run" signature="QFI.run(circuits, parameter_values, parameters=None, **options)">
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Run the job of the QFIs on the given circuits.
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**Parameters**
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* **circuits** – The list of quantum circuits to compute the QFIs.
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* **parameter\_values** – The list of parameter values to be bound to the circuit.
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* **parameters** – The sequence of parameters to calculate only the QFIs of the specified parameters. Each sequence of parameters corresponds to a circuit in `circuits`. Defaults to None, which means that the QFIs of all parameters in each circuit are calculated.
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* **options** – Primitive backend runtime options used for circuit execution. The order of priority is: options in `run` method > QFI’s default options > QGT’s default setting. Higher priority setting overrides lower priority setting.
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**Returns**
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The job object of the QFIs of the expectation values. The i-th result corresponds to `circuits[i]` evaluated with parameters bound as `parameter_values[i]`.
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</Function>
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### update\_default\_options
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<Function id="qiskit.algorithms.gradients.QFI.update_default_options" signature="QFI.update_default_options(**options)">
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Update the gradient’s default options setting.
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**Parameters**
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**\*\*options** – The fields to update the default options.
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</Function>
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## Attributes
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### options
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<Attribute id="qiskit.algorithms.gradients.QFI.options">
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Return the union of QGT’s options setting and QFI’s default options, where, if the same field is set in both, the QFI’s default options override the QGT’s default setting.
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**Return type**
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[`Options`](qiskit.providers.Options "qiskit.providers.options.Options")
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**Returns**
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The QFI default + QGT options.
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</Attribute>
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</Class>
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