• Accepted Paper

Ancilla-mediated fixed-point quantum search using Grover iterations

Yash Prabhat, Snigdha Thakur, and Ankur Raina

APS Open Sci. - Accepted 5 November, 2026

DOI: https://doi.org/10.1103/fg3v-2mx3

Abstract

Grover’s quantum search algorithm provides a fundamental quadratic speedup for unstructured datasets, reducing query complexity from 𝒪(N) to 𝒪(N). However, the algorithm’s reliance on precise iteration counts leads to the "soufflé problem," where over-rotation results in a sharp decline in success probability. This limitation is particularly restrictive when the number of solution states, M, is unknown. In this work, we present an ancilla-mediated fixed-point quantum search algorithm that achieves robust convergence by mapping the solution amplitude to a dedicated ancilla qubit. Unlike existing phase-matching fixed-point methods, our approach utilizes Grover’s real-plane reflections, thereby maintaining the intuitive geometric architecture of the original algorithm. We demonstrate that this method achieves a success probability of at least 92.6% with a query complexity of approximately 𝒪(N/M), effectively bridging the gap between standard amplitude amplification and robust fixed-point convergence.

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