87 lines
5.0 KiB
Plaintext
87 lines
5.0 KiB
Plaintext
---
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title: IterativePhaseEstimation
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description: API reference for qiskit.algorithms.IterativePhaseEstimation
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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.IterativePhaseEstimation
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---
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# IterativePhaseEstimation
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<Class id="qiskit.algorithms.IterativePhaseEstimation" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/algorithms/phase_estimators/ipe.py" signature="qiskit.algorithms.IterativePhaseEstimation(num_iterations, quantum_instance=None, sampler=None)" modifiers="class">
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Bases: `PhaseEstimator`
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Run the Iterative quantum phase estimation (QPE) algorithm.
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Given a unitary circuit and a circuit preparing an eigenstate, return the phase of the eigenvalue as a number in $[0,1)$ using the iterative phase estimation algorithm.
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**\[1]: Dobsicek et al. (2006), Arbitrary accuracy iterative phase estimation algorithm as a two**
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qubit benchmark, [arxiv/quant-ph/0610214](https://arxiv.org/abs/quant-ph/0610214)
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<Admonition title="Deprecated since version 0.24.0" type="danger">
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`qiskit.algorithms.phase_estimators.ipe.IterativePhaseEstimation.__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\_iterations** ([*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")) – The number of iterations (rounds) of the phase estimation to run.
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* **quantum\_instance** ([*QuantumInstance*](qiskit.utils.QuantumInstance "qiskit.utils.QuantumInstance") *|*[*Backend*](qiskit.providers.Backend "qiskit.providers.Backend") *| None*) – Deprecated: The quantum instance on which the circuit will be run.
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* **sampler** ([*BaseSampler*](qiskit.primitives.BaseSampler "qiskit.primitives.BaseSampler") *| None*) – The sampler primitive on which the circuit will be sampled.
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**Raises**
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* [**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError "(in Python v3.12)") – if num\_iterations is not greater than zero.
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* [**AlgorithmError**](algorithms#qiskit.algorithms.AlgorithmError "qiskit.algorithms.AlgorithmError") – If neither sampler nor quantum instance is provided.
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## Methods
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### construct\_circuit
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<Function id="qiskit.algorithms.IterativePhaseEstimation.construct_circuit" signature="construct_circuit(unitary, state_preparation, k, omega=0.0, measurement=False)">
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Construct the kth iteration Quantum Phase Estimation circuit.
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For details of parameters, see Fig. 2 in [https://arxiv.org/pdf/quant-ph/0610214.pdf](https://arxiv.org/pdf/quant-ph/0610214.pdf).
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**Parameters**
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* **unitary** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – The circuit representing the unitary operator whose eigenvalue (via phase) will be measured.
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* **state\_preparation** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – The circuit that prepares the state whose eigenphase will be measured. If this parameter is omitted, no preparation circuit will be run and input state will be the all-zero state in the computational basis.
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* **k** ([*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")) – the iteration idx.
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* **omega** ([*float*](https://docs.python.org/3/library/functions.html#float "(in Python v3.12)")) – the feedback angle.
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* **measurement** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) – Boolean flag to indicate if measurement should be included in the circuit.
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**Returns**
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the quantum circuit per iteration
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**Return type**
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[QuantumCircuit](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")
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</Function>
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### estimate
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<Function id="qiskit.algorithms.IterativePhaseEstimation.estimate" signature="estimate(unitary, state_preparation)">
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Estimate the eigenphase of the input unitary and initial-state pair.
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**Parameters**
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* **unitary** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – The circuit representing the unitary operator whose eigenvalue (via phase) will be measured.
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* **state\_preparation** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – The circuit that prepares the state whose eigenphase will be measured. If this parameter is omitted, no preparation circuit will be run and input state will be the all-zero state in the computational basis.
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**Returns**
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Estimated phase in an IterativePhaseEstimationResult object.
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**Raises**
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[**AlgorithmError**](algorithms#qiskit.algorithms.AlgorithmError "qiskit.algorithms.AlgorithmError") – If neither sampler nor quantum instance is provided.
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**Return type**
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*IterativePhaseEstimationResult*
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</Function>
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</Class>
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