qiskit_aer.utils.approximate_quantum_error

approximate_quantum_error(error, *, operator_string=None, operator_dict=None, operator_list=None)

Return a QuantumError object that approximates an error as a mixture of specified operators (channels).

The approximation is done by minimizing the Hilbert-Schmidt distance between the process matrix of the target error channel ($T$) and the process matrix of the output channel ($S = \sum_i{p_i S_i}$), i.e. $Tr[(T-S)^\dagger (T-S)]$, where $[p_1, p_2, ..., p_n]$ denote probabilities and $[S_1, S_2, ..., S_n]$ denote basis operators (channels).

See arXiv:1207.0046 for the details.

Parameters

• error (QuantumError or QuantumChannel) – the error to be approximated. The number of qubits must be 1 or 2.
• operator_string (string) – a name for a pre-made set of building blocks for the output channel (Default: None). Possible values are 'pauli', 'reset', 'clifford'.
• operator_dict (dict) – a dictionary whose values are the building blocks for the output channel (Default: None). E.g. {“x”: XGate(), “y”: YGate()}, keys “x” and “y” are not used in transformation.
• operator_list (list) – list of building block operators for the output channel (Default: None). E.g. [XGate(), YGate()]

Returns

the approximate quantum error.

Return type

QuantumError

Raises

• NoiseError – if any invalid argument is specified or approximation failed.
• MissingOptionalLibraryError – if cvxpy is not installed.