qiskit.algorithms.IterativePhaseEstimation

class IterativePhaseEstimation(num_iterations, quantum_instance=None)

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

Parameters

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

• quantum_instance (Union[Backend, BaseBackend, QuantumInstance, None]) – The quantum instance on which the circuit will be run.

Raises

ValueError – if num_iterations is not greater than zero.

__init__(num_iterations, quantum_instance=None)

Parameters

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

• quantum_instance (Union[Backend, BaseBackend, QuantumInstance, None]) – The quantum instance on which the circuit will be run.

Raises

ValueError – if num_iterations is not greater than zero.

Methods

__init__(num_iterations[, quantum_instance])	type num_iterations int
construct_circuit(unitary, state_preparation, k)	Construct the kth iteration Quantum Phase Estimation circuit.
estimate(unitary, state_preparation)	Estimate the eigenphase of the input unitary and initial-state pair.

construct_circuit(unitary, state_preparation, k, omega=0, measurement=False)

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)

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.

Return type

IterativePhaseEstimationResult

Returns

Estimated phase in an IterativePhaseEstimationResult object.