qiskit_addon_sqd.qubit.matrix_elements_from_pauli

matrix_elements_from_pauli(bitstring_matrix, pauli)[source]

Find the matrix elements of a Pauli operator in the subspace defined by the bitstrings.

Note

The bitstrings in the bitstring_matrix must be unique and sorted in ascending order according to their unsigned integer representation. Otherwise the projection will return wrong results. This function does not explicitly check for uniqueness and order because this can be rather time consuming. See qiskit_addon_sqd.qubit.sort_and_remove_duplicates() for a simple way to ensure your bitstring matrix is well-formatted.

Note

This function relies on jax to efficiently perform some calculations. jax converts the bit arrays to int64_t, which means the bit arrays in bitstring_matrix may not have length greater than 63.

Parameters:

  • bitstring_matrix (ndarray) – A 2D array of bool representations of bit values such that each row represents a single bitstring. The bitstrings in the matrix must be sorted according to their unsigned integer representations. Otherwise the projection will return wrong results.

  • pauli (Pauli) – A Pauli operator.

Returns:

A 1D array corresponding to the nonzero matrix elements A 1D array corresponding to the row indices of the elements A 1D array corresponding to the column indices of the elements

Raises:

ValueError – Bitstrings (rows) in bitstring_matrix must have length < 64.

Return type:

tuple[ndarray, ndarray, ndarray]