qiskit.algorithms.eval_observables
eval_observables(quantum_instance, quantum_state, observables, expectation, threshold=1e-12)
Deprecated: Accepts a list or a dictionary of operators and calculates their expectation values - means and standard deviations. They are calculated with respect to a quantum state provided. A user can optionally provide a threshold value which filters mean values falling below the threshold.
This function has been superseded by the qiskit.algorithms.observables_evaluator.eval_observables() function. It will be deprecated in a future release and subsequently removed after that.
The function qiskit.algorithms.aux_ops_evaluator.eval_observables() 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 function qiskit.algorithms.observables_evaluator.estimate_observables. See https://qisk.it/algo_migration for a migration guide.
Parameters
- quantum_instance (QuantumInstance |Backend) – A quantum instance used for calculations.
- quantum_state (Statevector |QuantumCircuit |OperatorBase) – An unparametrized quantum circuit representing a quantum state that expectation values are computed against.
- observables (ListOrDict[OperatorBase]) – A list or a dictionary of operators whose expectation values are to be calculated.
- expectation (ExpectationBase) – An instance of ExpectationBase which defines a method for calculating expectation values.
- threshold (float) – A threshold value that defines which mean values should be neglected (helpful for ignoring numerical instabilities close to 0).
Returns
A list or a dictionary of tuples (mean, standard deviation).
Raises
ValueError – If a quantum_state with free parameters is provided.
Return type
ListOrDict[tuple[complex, complex]]