qiskit.aqua.algorithms.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]¶

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

__init__(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]¶

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

`__init__`([operator, state_in, iqft, …])	type operator `Union`[`OperatorBase`, `LegacyBaseOperator`, `None`]
`compute_minimum_eigenvalue`([operator, …])	Computes minimum eigenvalue.
`construct_circuit`([measurement])	Construct circuit.
`run`([quantum_instance])	Execute the algorithm with selected backend.
`set_backend`(backend, **kwargs)	Sets backend with configuration.
`supports_aux_operators`()	Whether computing the expectation value of auxiliary operators is supported.

Attributes

`aux_operators`	Returns aux operators
`backend`	Returns backend.
`operator`	Returns operator
`quantum_instance`	Returns quantum instance.
`random`	Return a numpy random.

property aux_operators¶

Returns aux operators

Return type: Optional[List[Union[OperatorBase, LegacyBaseOperator]]]

property backend¶

Returns backend.

Return type: Union[Backend, BaseBackend]

compute_minimum_eigenvalue(operator=None, aux_operators=None)[source]¶

Computes minimum eigenvalue. Operator and aux_operators can be supplied here and if not None will override any already set into algorithm so it can be reused with different operators. While an operator is required by algorithms, aux_operators are optional. To ‘remove’ a previous aux_operators array use an empty list here.

Parameters

operator (Union[OperatorBase, LegacyBaseOperator, None]) – If not None replaces operator in algorithm
aux_operators (Optional[List[Union[OperatorBase, LegacyBaseOperator]]]) – If not None replaces aux_operators in algorithm

Return type

MinimumEigensolverResult

Returns

MinimumEigensolverResult

construct_circuit(measurement=False)[source]¶

Construct circuit.

Parameters: measurement (bool) – Boolean flag to indicate if measurement should be included in the circuit.
Returns: quantum circuit.
Return type: QuantumCircuit

property operator¶

Returns operator

Return type: Optional[LegacyBaseOperator]

property quantum_instance¶

Returns quantum instance.

Return type: Optional[QuantumInstance]

property random¶: Return a numpy random.

run(quantum_instance=None, **kwargs)¶

Execute the algorithm with selected backend.

Parameters

quantum_instance (Union[QuantumInstance, Backend, BaseBackend, None]) – the experimental setting.
kwargs (dict) – kwargs

Returns

results of an algorithm.

Return type

dict

Raises

AquaError – If a quantum instance or backend has not been provided

set_backend(backend, **kwargs)¶

Sets backend with configuration.

Return type: None

classmethod supports_aux_operators()¶

Whether computing the expectation value of auxiliary operators is supported.

If the minimum eigensolver computes an eigenstate of the main operator then it can compute the expectation value of the aux_operators for that state. Otherwise they will be ignored.

Return type: bool
Returns: True if aux_operator expectations can be evaluated, False otherwise