117 lines
5.2 KiB
Plaintext
117 lines
5.2 KiB
Plaintext
---
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title: LinCombQGT
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description: API reference for qiskit.algorithms.gradients.LinCombQGT
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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.LinCombQGT
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---
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# LinCombQGT
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<Class id="qiskit.algorithms.gradients.LinCombQGT" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.45/qiskit/algorithms/gradients/lin_comb/lin_comb_qgt.py" signature="qiskit.algorithms.gradients.LinCombQGT(estimator, phase_fix=True, derivative_type=DerivativeType.COMPLEX, options=None)" modifiers="class">
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Bases: [`BaseQGT`](qiskit.algorithms.gradients.BaseQGT "qiskit.algorithms.gradients.base.base_qgt.BaseQGT")
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Computes the Quantum Geometric Tensor (QGT) given a pure, parameterized quantum state.
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This method employs a linear combination of unitaries \[1].
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**Reference:**
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> **\[1]: Schuld et al., “Evaluating analytic gradients on quantum hardware” (2018).**
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>
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> [arXiv:1811.11184](https://arxiv.org/pdf/1811.11184.pdf)
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**Parameters**
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* **estimator** ([*BaseEstimator*](qiskit.primitives.BaseEstimator "qiskit.primitives.BaseEstimator")) – The estimator used to compute the QGT.
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* **phase\_fix** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) – Whether to calculate the second term (phase fix) of the QGT, which is $\langle\partial_i \psi | \psi \rangle \langle\psi | \partial_j \psi \rangle$. Default to `True`.
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* **derivative\_type** (*DerivativeType*) –
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The type of derivative. Can be either `DerivativeType.REAL` `DerivativeType.IMAG`, or `DerivativeType.COMPLEX`. Defaults to `DerivativeType.REAL`.
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* `DerivativeType.REAL` computes
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$$
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\mathrm{Re(QGT)}_{ij}= \mathrm{Re}[\langle \partial_i \psi | \partial_j \psi \rangle
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- \langle\partial_i \psi | \psi \rangle \langle\psi | \partial_j \psi \rangle].
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$$
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* `DerivativeType.IMAG` computes
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$$
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\mathrm{Re(QGT)}_{ij}= \mathrm{Im}[\langle \partial_i \psi | \partial_j \psi \rangle
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- \langle\partial_i \psi | \psi \rangle \langle\psi | \partial_j \psi \rangle].
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$$
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* `DerivativeType.COMPLEX` computes
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$$
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\mathrm{QGT}_{ij}= [\langle \partial_i \psi | \partial_j \psi \rangle
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- \langle\partial_i \psi | \psi \rangle \langle\psi | \partial_j \psi \rangle].
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$$
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* **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 > QGT’s default options > primitive’s default setting. Higher priority setting overrides lower priority setting.
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## Attributes
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### SUPPORTED\_GATES
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<Attribute id="qiskit.algorithms.gradients.LinCombQGT.SUPPORTED_GATES" attributeValue="['rx', 'ry', 'rz', 'rzx', 'rzz', 'ryy', 'rxx', 'cx', 'cy', 'cz', 'ccx', 'swap', 'iswap', 'h', 't', 's', 'sdg', 'x', 'y', 'z']" />
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### derivative\_type
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<Attribute id="qiskit.algorithms.gradients.LinCombQGT.derivative_type">
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The derivative type.
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</Attribute>
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### options
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<Attribute id="qiskit.algorithms.gradients.LinCombQGT.options">
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Return the union of estimator options setting and QGT default options, where, if the same field is set in both, the QGT’s default options override the primitive’s default setting.
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**Returns**
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The QGT default + estimator options.
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</Attribute>
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## Methods
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### run
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<Function id="qiskit.algorithms.gradients.LinCombQGT.run" signature="run(circuits, parameter_values, parameters=None, **options)">
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Run the job of the QGTs on the given circuits.
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**Parameters**
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* **circuits** (*Sequence\[*[*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")*]*) – The list of quantum circuits to compute the QGTs.
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* **parameter\_values** (*Sequence\[Sequence\[*[*float*](https://docs.python.org/3/library/functions.html#float "(in Python v3.12)")*]]*) – The list of parameter values to be bound to the circuit.
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* **parameters** (*Sequence\[Sequence\[*[*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.Parameter")*] | None] | None*) – The sequence of parameters to calculate only the QGTs of the specified parameters. Each sequence of parameters corresponds to a circuit in `circuits`. Defaults to None, which means that the QGTs 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 > QGT’s default options > primitive’s default setting. Higher priority setting overrides lower priority setting.
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**Returns**
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The job object of the QGTs of the expectation values. The i-th result corresponds to `circuits[i]` evaluated with parameters bound as `parameter_values[i]`.
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**Raises**
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[**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError "(in Python v3.12)") – Invalid arguments are given.
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**Return type**
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[AlgorithmJob](qiskit.algorithms.AlgorithmJob "qiskit.algorithms.AlgorithmJob")
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</Function>
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### update\_default\_options
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<Function id="qiskit.algorithms.gradients.LinCombQGT.update_default_options" signature="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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</Class>
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