Qubit encoding for a mixture of localized functions

One of the crucial generic techniques for quantum computation is the amplitude encoding. Although such techniques have been proposed, each of them often requires exponential classical-computational cost or an oracle whose explicit construction is not provided. Given the recent demands for practical quantum computation, we develop moderately specialized encoding techniques that generate an arbitrary linear combination of localized complex functions. We demonstrate that nloc discrete Lorentzian functions as an expansion basis set lead to efficient probabilistic encoding, whose computational time is O ( max ( nloc² log nloc, nloc² log nq, nq log nq )) for nq data qubits equipped with log₂ nloc ancillae. Furthermore, amplitude amplification in combination with amplitude reduction renders it deterministic with controllable errors and the computational time is reduced to O ( max ( nloc3/2 log nloc, nloc3/2 log nq, nq log nq )). We provide estimation of required resources for application of our scheme to quantum chemistry in real space. We also show the results on real superconducting quantum computers to confirm the validity of our techniques.