209 lines
9.6 KiB
Plaintext
209 lines
9.6 KiB
Plaintext
---
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title: AmplitudeEstimation
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description: API reference for qiskit.algorithms.AmplitudeEstimation
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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.AmplitudeEstimation
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---
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# AmplitudeEstimation
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<Class id="qiskit.algorithms.AmplitudeEstimation" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.24/qiskit/algorithms/amplitude_estimators/ae.py" signature="AmplitudeEstimation(num_eval_qubits, phase_estimation_circuit=None, iqft=None, quantum_instance=None, sampler=None)" modifiers="class">
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Bases: [`AmplitudeEstimator`](qiskit.algorithms.AmplitudeEstimator "qiskit.algorithms.amplitude_estimators.amplitude_estimator.AmplitudeEstimator")
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The Quantum Phase Estimation-based Amplitude Estimation algorithm.
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This class implements the original Quantum Amplitude Estimation (QAE) algorithm, introduced by \[1]. This canonical version uses quantum phase estimation along with a set of $m$ additional evaluation qubits to find an estimate $\tilde{a}$, that is restricted to the grid
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$$
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\tilde{a} \in \{\sin^2(\pi y / 2^m) : y = 0, ..., 2^{m-1}\}
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$$
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More evaluation qubits produce a finer sampling grid, therefore the accuracy of the algorithm increases with $m$.
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Using a maximum likelihood post processing, this grid constraint can be circumvented. This improved estimator is implemented as well, see \[2] Appendix A for more detail.
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<Admonition title="Note" type="note">
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This class does not support the [`EstimationProblem.is_good_state`](qiskit.algorithms.EstimationProblem#is_good_state "qiskit.algorithms.EstimationProblem.is_good_state") property, as for phase estimation-based QAE, the oracle that identifes the good states must be encoded in the Grover operator. To set custom oracles, the [`EstimationProblem.grover_operator`](qiskit.algorithms.EstimationProblem#grover_operator "qiskit.algorithms.EstimationProblem.grover_operator") attribute can be set directly.
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</Admonition>
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**References**
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**\[1]: Brassard, G., Hoyer, P., Mosca, M., & Tapp, A. (2000).**
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Quantum Amplitude Amplification and Estimation. [arXiv:quant-ph/0005055](http://arxiv.org/abs/quant-ph/0005055).
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**\[2]: Grinko, D., Gacon, J., Zoufal, C., & Woerner, S. (2019).**
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Iterative Quantum Amplitude Estimation. [arXiv:1912.05559](https://arxiv.org/abs/1912.05559).
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<Admonition title="Deprecated since version 0.24.0" type="danger">
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`qiskit.algorithms.amplitude_estimators.ae.AmplitudeEstimation.__init__()`’s argument `quantum_instance` is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. Instead, use the `sampler` argument. See [https://qisk.it/algo\_migration](https://qisk.it/algo_migration) for a migration guide.
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</Admonition>
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**Parameters**
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* **num\_eval\_qubits** (*int*) – The number of evaluation qubits.
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* **phase\_estimation\_circuit** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") *| None*) – The phase estimation circuit used to run the algorithm. Defaults to the standard phase estimation circuit from the circuit library, qiskit.circuit.library.PhaseEstimation when None.
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* **iqft** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") *| None*) – The inverse quantum Fourier transform component, defaults to using a standard implementation from qiskit.circuit.library.QFT when None.
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* **quantum\_instance** ([*QuantumInstance*](qiskit.utils.QuantumInstance "qiskit.utils.QuantumInstance") *|*[*Backend*](qiskit.providers.Backend "qiskit.providers.Backend") *| None*) – Deprecated: The backend (or QuantumInstance) to execute the circuits on.
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* **sampler** ([*BaseSampler*](qiskit.primitives.BaseSampler "qiskit.primitives.BaseSampler") *| None*) – A sampler primitive to evaluate the circuits.
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**Raises**
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**ValueError** – If the number of evaluation qubits is smaller than 1.
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## Methods
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<span id="qiskit-algorithms-amplitudeestimation-compute-confidence-interval" />
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### compute\_confidence\_interval
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<Function id="qiskit.algorithms.AmplitudeEstimation.compute_confidence_interval" signature="AmplitudeEstimation.compute_confidence_interval(result, alpha=0.05, kind='likelihood_ratio')" modifiers="static">
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Compute the (1 - alpha) confidence interval.
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**Parameters**
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* **result** ([*AmplitudeEstimationResult*](qiskit.algorithms.AmplitudeEstimationResult "qiskit.algorithms.AmplitudeEstimationResult")) – An amplitude estimation result for which to compute the confidence interval.
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* **alpha** (*float*) – Confidence level: compute the (1 - alpha) confidence interval.
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* **kind** (*str*) – The method to compute the confidence interval, can be ‘fisher’, ‘observed\_fisher’ or ‘likelihood\_ratio’ (default)
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**Returns**
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The (1 - alpha) confidence interval of the specified kind.
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**Raises**
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* **AquaError** – If ‘mle’ is not in self.\_ret.keys() (i.e. run was not called yet).
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* **NotImplementedError** – If the confidence interval method kind is not implemented.
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**Return type**
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tuple\[float, float]
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</Function>
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<span id="qiskit-algorithms-amplitudeestimation-compute-mle" />
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### compute\_mle
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<Function id="qiskit.algorithms.AmplitudeEstimation.compute_mle" signature="AmplitudeEstimation.compute_mle(result, apply_post_processing=False)" modifiers="static">
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Compute the Maximum Likelihood Estimator (MLE).
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**Parameters**
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* **result** ([*AmplitudeEstimationResult*](qiskit.algorithms.AmplitudeEstimationResult "qiskit.algorithms.AmplitudeEstimationResult")) – An amplitude estimation result object.
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* **apply\_post\_processing** (*bool*) – If True, apply the post processing to the MLE before returning it.
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**Returns**
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The MLE for the provided result object.
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**Return type**
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float
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</Function>
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<span id="qiskit-algorithms-amplitudeestimation-construct-circuit" />
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### construct\_circuit
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<Function id="qiskit.algorithms.AmplitudeEstimation.construct_circuit" signature="AmplitudeEstimation.construct_circuit(estimation_problem, measurement=False)">
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Construct the Amplitude Estimation quantum circuit.
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**Parameters**
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* **estimation\_problem** ([*EstimationProblem*](qiskit.algorithms.EstimationProblem "qiskit.algorithms.amplitude_estimators.estimation_problem.EstimationProblem")) – The estimation problem for which to construct the QAE circuit.
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* **measurement** (*bool*) – Boolean flag to indicate if measurements should be included in the circuit.
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**Returns**
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The QuantumCircuit object for the constructed circuit.
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**Return type**
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[*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")
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</Function>
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<span id="qiskit-algorithms-amplitudeestimation-estimate" />
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### estimate
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<Function id="qiskit.algorithms.AmplitudeEstimation.estimate" signature="AmplitudeEstimation.estimate(estimation_problem)">
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Run the amplitude estimation algorithm on provided estimation problem.
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**Parameters**
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**estimation\_problem** ([*EstimationProblem*](qiskit.algorithms.EstimationProblem "qiskit.algorithms.amplitude_estimators.estimation_problem.EstimationProblem")) – The estimation problem.
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**Returns**
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An amplitude estimation results object.
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**Raises**
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* **ValueError** – If state\_preparation or objective\_qubits are not set in the estimation\_problem.
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* **ValueError** – A quantum instance or sampler must be provided.
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* [**AlgorithmError**](qiskit.algorithms.AlgorithmError "qiskit.algorithms.AlgorithmError") – Sampler job run error.
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**Return type**
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[AmplitudeEstimationResult](qiskit.algorithms.AmplitudeEstimationResult "qiskit.algorithms.AmplitudeEstimationResult")
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</Function>
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<span id="qiskit-algorithms-amplitudeestimation-evaluate-measurements" />
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### evaluate\_measurements
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<Function id="qiskit.algorithms.AmplitudeEstimation.evaluate_measurements" signature="AmplitudeEstimation.evaluate_measurements(circuit_results, threshold=1e-06)">
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Evaluate the results from the circuit simulation.
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Given the probabilities from statevector simulation of the QAE circuit, compute the probabilities that the measurements y/gridpoints a are the best estimate.
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**Parameters**
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* **circuit\_results** (*dict\[str, int] | np.ndarray*) – The circuit result from the QAE circuit. Can be either a counts dict or a statevector or a quasi-probabilities dict.
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* **threshold** (*float*) – Measurements with probabilities below the threshold are discarded.
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**Returns**
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**Dictionaries containing the a gridpoints with respective probabilities and**
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y measurements with respective probabilities, in this order.
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**Return type**
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tuple\[dict\[float, float], dict\[int, float]]
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</Function>
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## Attributes
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### quantum\_instance
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<Attribute id="qiskit.algorithms.AmplitudeEstimation.quantum_instance">
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Get the quantum instance.
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<Admonition title="Deprecated since version 0.24.0" type="danger">
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The property `qiskit.algorithms.amplitude_estimators.ae.AmplitudeEstimation.quantum_instance` is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. See [https://qisk.it/algo\_migration](https://qisk.it/algo_migration) for a migration guide.
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</Admonition>
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**Returns**
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The quantum instance used to run this algorithm.
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**Type**
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Deprecated
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</Attribute>
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### sampler
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<Attribute id="qiskit.algorithms.AmplitudeEstimation.sampler">
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Get the sampler primitive.
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**Returns**
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The sampler primitive to evaluate the circuits.
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</Attribute>
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</Class>
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