EstimationProblem
class qiskit.algorithms.EstimationProblem(state_preparation, objective_qubits, grover_operator=None, post_processing=None, is_good_state=None)
Bases: object
The estimation problem is the input to amplitude estimation algorithm.
This class contains all problem-specific information required to run an amplitude estimation algorithm. That means, it minimally contains the state preparation and the specification of the good state. It can further hold some post processing on the estimation of the amplitude or a custom Grover operator.
Parameters
- state_preparation (QuantumCircuit) – A circuit preparing the input state, referred to as .
- objective_qubits (int |list[int]) – A single qubit index or a list of qubit indices to specify which qubits to measure. The
is_good_statefunction is applied on the bitstring of these objective qubits. - grover_operator (QuantumCircuit | None) – The Grover operator used as unitary in the phase estimation circuit.
- post_processing (Callable[[float], float] | None) – A mapping applied to the result of the algorithm , usually used to map the estimate to a target interval. Defaults to the identity.
- is_good_state (Callable[[str], bool] | None) – A function to check whether a string represents a good state. Defaults to all objective qubits being in state .
Attributes
grover_operator
Get the operator, or Grover operator.
If the Grover operator is not set, we try to build it from the operator and objective_qubits. This only works if objective_qubits is a list of integers.
Returns
The Grover operator, or None if neither the Grover operator nor the operator is set.
has_good_state
Check whether an is_good_state function is set.
Some amplitude estimators, such as AmplitudeEstimation do not support a custom implementation of the is_good_state function, and can only handle the default.
Returns
True, if a custom is_good_state is set, otherwise returns False.
is_good_state
Checks whether a bitstring represents a good state.
Returns
Handle to the is_good_state callable.
objective_qubits
Get the criterion for a measurement outcome to be in a ‘good’ state.
Returns
The criterion as list of qubit indices.
post_processing
Apply post processing to the input value.
Returns
A handle to the post processing function. Acts as identity by default.
state_preparation
Get the operator encoding the amplitude .
Returns
The operator as QuantumCircuit.
Methods
rescale
rescale(scaling_factor)
Rescale the good state amplitude in the estimation problem.
Parameters
scaling_factor (float) – The scaling factor in [0, 1].
Returns
A rescaled estimation problem.
Return type