"Quantum supremacy" revisited: Lowcomplexity, deterministic solutions of the original DeutschJozsa problem in classical physical systems
Abstract
The original DeutschJozsa (oDJ) problem is for an oracle (realized here as a database) of size N, where, according to their claim, the deterministic solution of the problem on a classical Turing computer requires O(N) computational complexity. They produced the famous DeutschJozsa quantum algorithm that offered an exponential speedup over the classical computer, namely O[log(N)] complexity for the solution in a quantum computer. In this paper, the problem is implemented on an instantaneous noisebased logic processor. It is shown that, similarly to the quantum algorithm, the oDJ problem can deterministically be solved with O[log(N)] complexity. The implication is that by adding a truly random coin to a classical Turing machine and using this classicalphysical algorithm can also speed up the deterministic solution of the DeutschJozsa problem exponentially, similarly to the quantum algorithm. Then it is realized that the same database and the solution of the DeutschJozsa problem can also be realized by using an identical algorithmic structure in a simpler way, even without noise/random coin. The only lost function in this new system, as compared to noisebased logic, is the ability to do generic parallel logic operations over the whole database. As the latter feature is not needed for the oDJ problem, it is concluded that the problem can be solved on a classical computer with O[log(N)] complexity even without a random coin. Therefore, while the oDJ algorithm is historically important step in the developments of quantum computers, it is insufficient to prove quantum supremacy. Note, there is also simplified DeutschJozsa problem proposed later, which is more popular in the field, however it is irrelevant for the present paper.
 Publication:

arXiv eprints
 Pub Date:
 October 2022
 DOI:
 10.48550/arXiv.2210.07088
 arXiv:
 arXiv:2210.07088
 Bibcode:
 2022arXiv221007088K
 Keywords:

 Physics  General Physics
 EPrint:
 Revised version: original DJ problem