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arXiv · 2506.06435

Quantum mechanics can find a needle in a haystack every time

Fatemeh Mohit·Joshua Guanzon·Jaden McKinlay·Till J. Weinhold·Casey R. Myers·Marcelo P. Almeida·Markus Rambach·Andrew G. White
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Abstract

Grover's algorithm is one of the pioneering demonstrations of the advantages of quantum computing over its classical counterpart, providing - at most - a quadratic speed-up over the classical solution for unstructured database search. The original formulation of Grover's algorithm is non-deterministic, finding the answer with a probability that varies with the size of the search space and the number of marked elements. A recent reformulation introduced a deterministic form of Grover's algorithm that - in principle - finds the answer with certainty. Here we realise the deterministic Grover's algorithm on a programmable photonic integrated circuit, finding that it not only outperforms the original Grover's algorithm as predicted, but is also markedly more robust against technological imperfections. We explore databases of 4 to 10 elements, with every choice of a single marked element, achieving an average success probability of $99.77 \pm 0.05\%$.

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Fatemeh Mohit, Joshua Guanzon, Jaden McKinlay, Till J. Weinhold, Casey R. Myers, Marcelo P. Almeida, Markus Rambach, Andrew G. White. 2025-06-06. Quantum mechanics can find a needle in a haystack every time. https://arxiv.org/abs/2506.06435

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