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qiskit.algorithms.AmplitudeEstimation(num_eval_qubits, phase_estimation_circuit=None, iqft=None, quantum_instance=None, sampler=None)

GitHub(opens in a new tab)

Bases: AmplitudeEstimator

The Quantum Phase Estimation-based Amplitude Estimation algorithm.

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 mm additional evaluation qubits to find an estimate a~\tilde{a}, that is restricted to the grid

a~{sin2(πy/2m):y=0,...,2m1}\tilde{a} \in \{\sin^2(\pi y / 2^m) : y = 0, ..., 2^{m-1}\}

More evaluation qubits produce a finer sampling grid, therefore the accuracy of the algorithm increases with mm.

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.


This class does not support the 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 attribute can be set directly.


[1]: Brassard, G., Hoyer, P., Mosca, M., & Tapp, A. (2000).

Quantum Amplitude Amplification and Estimation. arXiv:quant-ph/0005055(opens in a new tab).

[2]: Grinko, D., Gacon, J., Zoufal, C., & Woerner, S. (2019).

Iterative Quantum Amplitude Estimation. arXiv:1912.05559(opens in a new tab).

Deprecated since version 0.24.0’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 in a new tab) for a migration guide.


  • num_eval_qubits (int(opens in a new tab)) – The number of evaluation qubits.
  • phase_estimation_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.
  • iqft (QuantumCircuit | None) – The inverse quantum Fourier transform component, defaults to using a standard implementation from qiskit.circuit.library.QFT when None.
  • quantum_instance (QuantumInstance |Backend | None) – Deprecated: The backend (or QuantumInstance) to execute the circuits on.
  • sampler (BaseSampler | None) – A sampler primitive to evaluate the circuits.


ValueError(opens in a new tab) – If the number of evaluation qubits is smaller than 1.



Get the quantum instance.

Deprecated since version 0.24.0

The property is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. See in a new tab) for a migration guide.


The quantum instance used to run this algorithm.




Get the sampler primitive.


The sampler primitive to evaluate the circuits.



static compute_confidence_interval(result, alpha=0.05, kind='likelihood_ratio')

Compute the (1 - alpha) confidence interval.


  • result (AmplitudeEstimationResult) – An amplitude estimation result for which to compute the confidence interval.
  • alpha (float(opens in a new tab)) – Confidence level: compute the (1 - alpha) confidence interval.
  • kind (str(opens in a new tab)) – The method to compute the confidence interval, can be ‘fisher’, ‘observed_fisher’ or ‘likelihood_ratio’ (default)


The (1 - alpha) confidence interval of the specified kind.


NotImplementedError(opens in a new tab) – If the confidence interval method kind is not implemented.

Return type

tuple(opens in a new tab)[float(opens in a new tab), float(opens in a new tab)]


static compute_mle(result, apply_post_processing=False)

Compute the Maximum Likelihood Estimator (MLE).



The MLE for the provided result object.

Return type

float(opens in a new tab)


construct_circuit(estimation_problem, measurement=False)

Construct the Amplitude Estimation quantum circuit.


  • estimation_problem (EstimationProblem) – The estimation problem for which to construct the QAE circuit.
  • measurement (bool(opens in a new tab)) – Boolean flag to indicate if measurements should be included in the circuit.


The QuantumCircuit object for the constructed circuit.

Return type




Run the amplitude estimation algorithm on provided estimation problem.


estimation_problem (EstimationProblem) – The estimation problem.


An amplitude estimation results object.


Return type



evaluate_measurements(circuit_results, threshold=1e-06)

Evaluate the results from the circuit simulation.

Given the probabilities from statevector simulation of the QAE circuit, compute the probabilities that the measurements y/gridpoints a are the best estimate.



Dictionaries containing the a gridpoints with respective probabilities and

y measurements with respective probabilities, in this order.

Return type

tuple(opens in a new tab)[dict(opens in a new tab)[float(opens in a new tab), float(opens in a new tab)], dict(opens in a new tab)[int(opens in a new tab), float(opens in a new tab)]]

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