IterativePhaseEstimation

class qiskit.algorithms.IterativePhaseEstimation(num_iterations, quantum_instance=None, sampler=None)[source]

Bases: PhaseEstimator

Run the Iterative quantum phase estimation (QPE) algorithm.

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.

[1]: Dobsicek et al. (2006), Arbitrary accuracy iterative phase estimation algorithm as a two

qubit benchmark, arxiv/quant-ph/0610214

Deprecated since version 0.24.0: 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 for a migration guide.

Parameters:

  • num_iterations (int) – The number of iterations (rounds) of the phase estimation to run.

  • quantum_instance (QuantumInstance | Backend | None) – Deprecated: The quantum instance on which the circuit will be run.

  • sampler (BaseSampler | None) – The sampler primitive on which the circuit will be sampled.

Raises:

  • ValueError – if num_iterations is not greater than zero.

  • AlgorithmError – If neither sampler nor quantum instance is provided.

Methods

construct_circuit(unitary, state_preparation, k, omega=0.0, measurement=False)[source]

Construct the kth iteration Quantum Phase Estimation circuit.

For details of parameters, see Fig. 2 in https://arxiv.org/pdf/quant-ph/0610214.pdf.

Parameters:

  • unitary (QuantumCircuit) – The circuit representing the unitary operator whose eigenvalue (via phase) will be measured.

  • state_preparation (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.

  • k (int) – the iteration idx.

  • omega (float) – the feedback angle.

  • measurement (bool) – Boolean flag to indicate if measurement should be included in the circuit.

Returns:

the quantum circuit per iteration

Return type:

QuantumCircuit

estimate(unitary, state_preparation)[source]

Estimate the eigenphase of the input unitary and initial-state pair.

Parameters:

  • unitary (QuantumCircuit) – The circuit representing the unitary operator whose eigenvalue (via phase) will be measured.

  • state_preparation (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.

Returns:

Estimated phase in an IterativePhaseEstimationResult object.

Raises:

AlgorithmError – If neither sampler nor quantum instance is provided.

Return type:

IterativePhaseEstimationResult