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arXiv:2610.04024

Accelerated search for global extrema in structured quantum signals

Sachin S. Bharadwaj, Katepalli R. Sreenivasan

quant-phcs.CEphysics.app-phphysics.comp-phphysics.flu-dynSubmitted Oct 2, 2026• Announced Oct 6, 2026• 0 citations
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Abstract

Extreme values of a physical system are rare by definition, yet they can govern some of its most consequential and anomalous behavior. Their sparsity makes them particularly costly to identify in large data sets. Quantum computation offers a potential way to reduce this cost. The challenge is that quantum amplitudes cannot simply be read, copied, compared, or marked using conventional search oracles. Here we introduce an algorithm for searching amplitude-encoded quantum signals that exploits their underlying structure. Through a nonlinear amplitude transformation, the algorithm identifies and certifies a global extremum while exponentially reducing the effective search space for structured signals. We establish a polylogarithmic query complexity in the data size $N$, together with global completeness, efficient classical verification, and a measurable criterion for quantifying exploitable structure. We demonstrate the framework using computational turbulence data. Applied to line cuts of velocity gradients from a $1024^3$ simulation containing more than one billion grid points, the algorithm consistently isolates the extreme tail and reduces the median search space to $O(\log N)$. The clustered structure characteristic of turbulence further accelerates the search. These results establish a direct connection between physical structure and quantum advantage in extreme-value search. For accessibility, the main text emphasizes the central ideas and results, while the theoretical derivations are provided in the Appendices.

Comments
33 pages, 5 figures, 2 tables

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Extreme values of a physical system are rare by definition, yet they can govern some of its most consequential and anomalous behavior. Their sparsity makes them particularly costly to identify in large data sets. Quantum computation offers a potential way to reduce this cost. The challenge is that quantum amplitudes cannot simply be read, copied, compared, or marked using conventional search oracles. Here we introduce an algorithm for searching amplitude-encoded quantum signals that exploits their underlying structure. Through a nonlinear amplitude transformation, the algorithm identifies and certifies a global extremum while exponentially reducing the effective search space for structured signals. We establish a polylogarithmic query complexity in the data size NNN, together with global completeness, efficient classical verification, and a measurable criterion for quantifying exploitable structure. We demonstrate the framework using computational turbulence data. Applied to line cuts of velocity gradients from a 102431024^310243 simulation containing more than one billion grid points, the algorithm consistently isolates the extreme tail and reduces the median search space to O(log⁡N)O(\log N)O(logN). The clustered structure characteristic of turbulence further accelerates the search. These results establish a direct connection between physical structure and quantum advantage in extreme-value search. For accessibility, the main text emphasizes the central ideas and results, while the theoretical derivations are provided in the Appendices.
Oracle-based quantum computation reframes efficiency from classical time/space costs to query complexity, i.e., the number of accesses to a black-box unitary oracle Uf needed to reveal a hidden property or target state. This study comparatively analyzes query complexity across four canonical oracle-driven algorithms—Deutsch’s, Bernstein–Vazirani, Grover’s search, and Amplitude Amplification—to clarify how superposition, entanglement, interference, and phase kickback translate into provable speedups independent of hardware details. The objective is to systematically connect oracle structure to achievable quantum advantage by contrasting exact, single-query interference algorithms with iterative, probabilistic rotation-based algorithms, and by benchmarking classical deterministic/probabilistic query requirements against quantum bounds. Methodologically, we (i) mathematically model Deutsch and Bernstein–Vazirani via stepwise state-vector evolution to expose phase kickback and phase-encoded answer extraction in one oracle call, (ii) geometrically track Grover and Amplitude Amplification as two-dimensional state-space rotations, quantifying how repeated oracle-driven reflections amplify success amplitude, and (iii) compute classical query baselines and compare them directly with quantum query scaling. Results show that Deutsch reduces classical 2 queries to exactly 1 quantum query for constant-versus-balanced testing, while Bernstein–Vazirani deterministically recovers an n-bit hidden string s with (O(1)) quantum queries versus (O(n)) classical queries. For unstructured search over (N=2n) items, Grover achieves a bounded-error quadratic improvement from (O(N)) to (O(√{N}) queries, and Amplitude Amplification generalizes this to boost success probability from (p) to near certainty in O (1/√p) oracle applications. The central implication is a structural divide: rigid algebraic structure permits maximal, single-query speedups, whereas unstructured “chaos” necessitates iterative geometric amplification, which is more broadly applicable but demands highly stable, error-corrected hardware; consequently, quantum systems are best viewed as specialized co-processors activated when oracle structure warrants a quantum shortcut.
Quantum search is among the most important algorithms in quantum computing. At its core is quantum amplitude amplification, a technique that achieves a quadratic speedup over classical search by combining two global reflections: the oracle, which marks the target, and the diffusion operator, which reflects about the initial state. We show that this speedup can be preserved when the oracle is the only global operator, with all other operations acting locally on non-overlapping partitions of the search register. We present a recursive construction that, when the initial and target states both decompose as tensor products over these chosen partitions, admits an exact closed-form solution for the algorithm's dynamics. This is enabled by an intriguing degeneracy in the principal angles between successive reflections, which collapse to just two distinct values governed by a single recursively defined angle. Applied to unstructured search, a problem that naturally satisfies the tensor decomposition, the approach retains the O(N)O(\sqrt{N})O(N​) oracle complexity of Grover search when each partition contains at least log⁡2(log⁡2N)\log_2(\log_2 N)log2​(log2​N) qubits. On an 18-qubit search problem, partitioning into two stages reduces the non-oracle circuit depth by as much as 51%-96% relative to Grover, requiring up to 9% additional oracle calls. For larger problem sizes this oracle overhead rapidly diminishes, and valuable depth reductions persist when the oracle circuit is substantially deeper than the diffusion operator. More broadly, these results show that a global diffusion operator is not necessary to achieve the quadratic speedup in quantum search, offering a new perspective on this foundational algorithm. Moreover, the scalar reduction at the heart of our analysis inspires and motivates new directions and innovations in quantum algorithm design and evaluation.
Introduction We present Quantum Adaptive Search (QAGS), a hybrid quantum-classical algorithm for global optimization of multivariate functions. The method employs an adaptive mechanism that dynamically narrows the search space based on a quantum-estimated probability distribution of the objective function. Methods A quantum state encodes information about solution quality through a complex-amplitude mapping, enabling identification of promising regions and progressive tightening of the search bounds; a classical optimizer then performs local refinement. The analysis shows contraction of the search space toward global optima with controlled computational complexity. Results In simulation on standard benchmarks (Rastrigin, Styblinski-Tang, Rosenbrock), QAGS attains solutions at or near the true minima with very small absolute errors. Against an Adaptive Grid Search on the Sphere function, QAGS achieves comparable accuracy and shows increasing efficiency with dimensionality. Discussion These results indicate that amplitude-encoded region selection combined with classical refinement effectively contracts the search space and can reduce time and space requirements, especially at higher dimensions, while practical hardware implementations of amplitude encoding remain challenging.
Symbolic regression is a powerful technique for automatically discovering mathematical equations from data. However, its performance is often limited by the computational cost of exploring the exponentially large space of possible equations. This paper presents a novel approach that integrates symbolic regression with quantum amplitude estimation (QAE) to accelerate the equation discovery process. The core idea is to utilize QAE to efficiently estimate the probability amplitude of different equation candidates, thereby reducing the search time. We formulate the symbolic regression problem as a quantum optimization task and demonstrate, through theoretical analysis and a conceptual framework, the potential for significant speedups. The proposed method addresses the inherent challenges of symbolic regression by exploiting the parallel processing capabilities of quantum computers. The results suggest that quantum-enhanced symbolic regression holds promise for tackling complex datasets and discovering intricate mathematical relationships that would be intractable for classical symbolic regression algorithms. The key contribution lies in the application of QAE within the symbolic regression framework, offering a pathway toward faster and more accurate equation modeling.
Large-scale combinatorial optimization problems, arising in diverse fields such as logistics, finance, and operations research, pose a significant challenge to classical optimization algorithms. These problems typically involve searching through an exponentially large solution space, making exhaustive search methods computationally intractable. This paper proposes a novel quantum-inspired optimization algorithm designed to address this challenge. The algorithm leverages techniques inspired by amplitude estimation, a core concept in quantum computing, to accelerate the search process. Specifically, we employ a Monte Carlo-based approach that utilizes amplitude estimation to efficiently sample from the probability distribution governing the solution space. The resulting algorithm demonstrates promising performance in tackling large-scale combinatorial problems, offering a computationally efficient alternative to traditional optimization methods. We demonstrate the algorithm's effectiveness through theoretical analysis and provide insights into its advantages and limitations. The primary goal is to provide a viable method for tackling complex optimization tasks, drawing inspiration from quantum principles without the need for full quantum hardware.
We present a quantum algorithm for estimating the amplitude content of user-specified sequency bands in quantum-encoded signals. The method employs a sequency-ordered Quantum Walsh-Hadamard Transform (QWHT), a comparator-based oracle that coherently marks basis states within an arbitrary sequency range, and Quantum Amplitude Estimation (QAE) to estimate the total probability mass in the selected band. This enables the detection of structured signal components, including both high- and low-sequency features, as well as the identification of rapid sign-change behavior associated with noise or anomalies. The proposed method can be embedded as a module within a larger quantum algorithm; in this setting, both the input and output remain fully quantum, enabling seamless integration with upstream and downstream quantum operations. We show that the sequency-ordered QWHT can be implemented with circuit depth O(log⁡2N)O(\log_2 N)O(log2​N) (equivalently O(n)O(n)O(n) for N=2nN=2^nN=2n) when acting on an amplitude-encoded quantum state, whereas computing the full Walsh-Hadamard spectrum of an explicit length-NNN classical signal requires O(Nlog⁡2N)O(N\log_2 N)O(Nlog2​N) operations via the fast Walsh-Hadamard transform. This results in an exponential quantum advantage when the QWHT is used as a modular block within a larger quantum algorithm, relative to classical fast Walsh-Hadamard transform-based approaches operating on explicit data. From an application perspective, the proposed sequency band-energy estimation may be interpreted as a structure-based anomaly indicator, enabling the detection of unexpected high-sequency components relative to a nominal low-sequency signal class. The algorithm is applicable to quantum-enhanced signal processing tasks such as zero-crossing analysis, band-limited noise estimation, and feature extraction in the Walsh basis.