# QPE¶

class QPE(operator=None, state_in=None, iqft=None, num_time_slices=1, num_ancillae=1, expansion_mode='trotter', expansion_order=1, shallow_circuit_concat=False, quantum_instance=None)[source]

Bases: qiskit.aqua.algorithms.quantum_algorithm.QuantumAlgorithm, qiskit.aqua.algorithms.minimum_eigen_solvers.minimum_eigen_solver.MinimumEigensolver

The Quantum Phase Estimation algorithm.

QPE (also sometimes abbreviated as PEA, for Phase Estimation Algorithm), has two quantum registers, control and target, where the control consists of several qubits initially put in uniform superposition, and the target a set of qubits prepared in an eigenstate (often a guess of the eigenstate) of the unitary operator of a quantum system. QPE then evolves the target under the control using dynamics on the unitary operator. The information of the corresponding eigenvalue is then 'kicked-back' into the phases of the control register, which can then be deconvoluted by an Inverse Quantum Fourier Transform (IQFT), and measured for read-out in binary decimal format. QPE also requires a reasonably good estimate of the eigen wave function to start the process. For example, when estimating molecular ground energies in chemistry, the Hartree-Fock method could be used to provide such trial eigen wave functions.

Parameters
• operator (Union[OperatorBase, LegacyBaseOperator, None]) -- The Hamiltonian Operator

• state_in (Union[QuantumCircuit, InitialState, None]) -- An optional InitialState component representing an initial quantum state. None may be supplied.

• iqft (Optional[QuantumCircuit]) -- A Inverse Quantum Fourier Transform component

• num_time_slices (int) -- The number of time slices, has a minimum value of 1.

• num_ancillae (int) -- The number of ancillary qubits to use for the measurement, has a min. value of 1.

• expansion_mode (str) -- The expansion mode ('trotter'|'suzuki')

• expansion_order (int) -- The suzuki expansion order, has a min. value of 1.

• shallow_circuit_concat (bool) -- Set True to use shallow (cheap) mode for circuit concatenation of evolution slices. By default this is False. See qiskit.aqua.operators.common.evolution_instruction() for more information.

• quantum_instance (Union[QuantumInstance, Backend, BaseBackend, None]) -- Quantum Instance or Backend

Methods

 compute_minimum_eigenvalue Computes minimum eigenvalue. construct_circuit Construct circuit. run Execute the algorithm with selected backend. set_backend Sets backend with configuration. supports_aux_operators Whether computing the expectation value of auxiliary operators is supported.

Attributes

aux_operators

Returns aux operators

Return type

Optional[List[Union[OperatorBase, LegacyBaseOperator]]]

backend

Returns backend.

Return type

Union[Backend, BaseBackend]

operator

Returns operator

Return type

Optional[LegacyBaseOperator]

quantum_instance

Returns quantum instance.

Return type

Optional[QuantumInstance]

random

Return a numpy random.