{"id":244113,"date":"2025-10-22T18:04:15","date_gmt":"2025-10-22T18:04:15","guid":{"rendered":"https:\/\/www.newsbeep.com\/us\/244113\/"},"modified":"2025-10-22T18:04:15","modified_gmt":"2025-10-22T18:04:15","slug":"optimization-by-decoded-quantum-interferometry","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us\/244113\/","title":{"rendered":"Optimization by decoded quantum interferometry"},"content":{"rendered":"<p>NP-hardness results indicate that finding exact optima and even sufficiently good approximate optima for worst-case instances of many optimization problems is probably out of reach for polynomial-time algorithms both classical and quantum<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 4\" title=\"Trevisan, L. in Paradigms of Combinatorial Optimization: Problems and New Approaches 2nd edn (ed. Paschos, V. Th.) Ch. 13 (Wiley, 2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR4\" id=\"ref-link-section-d15498388e524\" rel=\"nofollow noopener\" target=\"_blank\">4<\/a>. Nevertheless, there remain combinatorial optimization problems, such as the closest vector problem, for which there is a large gap between the best approximation achieved by a polynomial-time classical algorithm<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Ajtai, M., Kumar, R. &amp; Sivakumar, D. A sieve algorithm for the shortest lattice vector problem. In Proc. 33rd Annual ACM Symposium on Theory of Computing 601&#x2013;610 (ACM, 2001).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR5\" id=\"ref-link-section-d15498388e528\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a> and the strongest complexity-theoretic inapproximability result<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 6\" title=\"Moshkovitz, D. The projection games conjecture and the NP-hardness of ln n-approximating set-cover. Theory Comput. 11, 221&#x2013;235 (2015).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR6\" id=\"ref-link-section-d15498388e532\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>. When considering average-case complexity, such gaps become more prevalent, as few average-case inapproximability results are known. These gaps present a potential opportunity for quantum computers, namely achieving in polynomial time an approximation that requires superpolynomial time to achieve using known classical algorithms.<\/p>\n<p>Quantum algorithms for combinatorial optimization have been the subject of intense research over the last three decades<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Farhi, E. et al. A quantum adiabatic evolution algorithm applied to random instances of an NP-complete problem. Science 292, 472&#x2013;475 (2001).\" href=\"#ref-CR7\" id=\"ref-link-section-d15498388e539\">7<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Farhi, E., Goldstone, J. &amp; Gutmann, S. A quantum approximate optimization algorithm applied to a bounded occurrence constraint problem. Preprint at &#10;                https:\/\/arxiv.org\/abs\/1412.6062&#10;                &#10;               (2014).\" href=\"#ref-CR8\" id=\"ref-link-section-d15498388e539_1\">8<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Hastings, M. B. A short path quantum algorithm for exact optimization. Quantum 2, 78 (2018).\" href=\"#ref-CR9\" id=\"ref-link-section-d15498388e539_2\">9<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Basso, J., Farhi, E., Marwaha, K., Villalonga, B. &amp; Zhou, L. The quantum approximate optimization algorithm at high depth for MaxCut on large-girth regular graphs and the Sherrington-Kirkpatrick model. In Proc. 17th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2022) (eds Le Gall, F. &amp; Morimae, T.) 7:1&#x2013;7:21 (Dagstuhl, 2022).\" href=\"#ref-CR10\" id=\"ref-link-section-d15498388e539_3\">10<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Dalzell, A. M., Pancotti, N., Campbell, E. T. &amp; Brand&#xE3;o, F. G. S. L. Mind the gap: achieving a super-Grover quantum speedup by jumping to the end. In Proc. 55th Annual ACM Symposium on Theory of Computing (STOC) (eds Saha, B. &amp; Servedio, R. A.) 1131&#x2013;1144 (ACM, 2023).\" href=\"#ref-CR11\" id=\"ref-link-section-d15498388e539_4\">11<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Kapit, E. et al. On the approximability of random-hypergraph MAX-3-XORSAT problems with quantum algorithms. Preprint at &#10;                https:\/\/arxiv.org\/abs\/2312.06104&#10;                &#10;               (2023).\" href=\"#ref-CR12\" id=\"ref-link-section-d15498388e539_5\">12<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 13\" title=\"Shaydulin, R. et al. Evidence of scaling advantage for the quantum approximate optimization algorithm on a classically intractable problem. Sci. Adv. 10, eadm6761 (2024).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR13\" id=\"ref-link-section-d15498388e542\" rel=\"nofollow noopener\" target=\"_blank\">13<\/a>, which has uncovered some evidence of a possible superpolynomial quantum speed-up for certain optimization problems<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Farhi, E., Gutmann, S., Ranard, D. &amp; Villalonga, B. Lower bounding the MaxCut of high girth 3-regular graphs using the QAOA. Preprint at &#10;                https:\/\/arxiv.org\/abs\/2503.12789&#10;                &#10;               (2025).\" href=\"#ref-CR14\" id=\"ref-link-section-d15498388e546\">14<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Leng, J., Zheng, Y. &amp; Wu, X. A quantum-classical performance separation in nonconvex optimization. Preprint at &#10;                https:\/\/arxiv.org\/abs\/2311.00811&#10;                &#10;               (2023).\" href=\"#ref-CR15\" id=\"ref-link-section-d15498388e546_1\">15<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Chen, Y., Liu, Q. &amp; Zhandry, M. Quantum algorithms for variants of average-case lattice problems via filtering. In Proc. Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT) (eds Dunkelman, O. &amp; Dziembowski, S.) 372&#x2013;401 (Springer, 2022).\" href=\"#ref-CR16\" id=\"ref-link-section-d15498388e546_2\">16<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Pirnay, N., Ulitzsh, V., Wilde, F., Eisert, J. &amp; Seifert, J.-P. An in-principle super-polynomial quantum advantage for approximating combinatorial optimization problems via computational learning theory. Sci. Adv. 10, eadj5170 (2024).\" href=\"#ref-CR17\" id=\"ref-link-section-d15498388e546_3\">17<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Szegedy, M. Quantum advantage for combinatorial optimization problems, simplified. Preprint at &#10;                https:\/\/arxiv.org\/abs\/2212.12572&#10;                &#10;               (2022).\" href=\"#ref-CR18\" id=\"ref-link-section-d15498388e546_4\">18<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Gily&#xE9;n, A., Hastings, M. B. &amp; Vazirani, U. (Sub)exponential advantage of adiabatic quantum computation with no sign problem. In Proc. 53rd Annual ACM SIGACT Symposium on Theory of Computing (STOC) (eds Khuller, S. &amp; Vassilevska Williams, V.) 1357&#x2013;1369 (ACM, 2021).\" href=\"#ref-CR19\" id=\"ref-link-section-d15498388e546_5\">19<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 20\" title=\"Eldar, L. &amp; Hallgren, S. An efficient quantum algorithm for lattice problems achieving subexponential approximation factor. Preprint at &#010;                https:\/\/arxiv.org\/abs\/2201.13450&#010;                &#010;               (2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR20\" id=\"ref-link-section-d15498388e549\" rel=\"nofollow noopener\" target=\"_blank\">20<\/a>. Nevertheless, the problem of finding a superpolynomial quantum advantage for optimization is extremely challenging and remains largely open.<\/p>\n<p>Here we propose a quantum algorithm for optimization that uses interference patterns as its main underlying principle. We call this algorithm decoded quantum interferometry (DQI). DQI uses a quantum Fourier transform to arrange that amplitudes interfere constructively on symbol strings for which the objective value is large, thereby enhancing the probability of obtaining good solutions upon measurement. Most previous approaches to quantum optimization have been Hamiltonian-based<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 7\" title=\"Farhi, E. et al. A quantum adiabatic evolution algorithm applied to random instances of an NP-complete problem. Science 292, 472&#x2013;475 (2001).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR7\" id=\"ref-link-section-d15498388e556\" rel=\"nofollow noopener\" target=\"_blank\">7<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 8\" title=\"Farhi, E., Goldstone, J. &amp; Gutmann, S. A quantum approximate optimization algorithm applied to a bounded occurrence constraint problem. Preprint at &#010;                https:\/\/arxiv.org\/abs\/1412.6062&#010;                &#010;               (2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR8\" id=\"ref-link-section-d15498388e559\" rel=\"nofollow noopener\" target=\"_blank\">8<\/a>, with a notable exception being the superpolynomial speed-up due to Chen, Liu and Zhandry<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 16\" title=\"Chen, Y., Liu, Q. &amp; Zhandry, M. Quantum algorithms for variants of average-case lattice problems via filtering. In Proc. Annual International Conference on the Theory and Applications of Cryptographic Techniques (EUROCRYPT) (eds Dunkelman, O. &amp; Dziembowski, S.) 372&#x2013;401 (Springer, 2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR16\" id=\"ref-link-section-d15498388e563\" rel=\"nofollow noopener\" target=\"_blank\">16<\/a> for finding short lattice vectors, which uses Fourier transforms and can be seen as an ancestor of DQI. Whereas Hamiltonian-based quantum optimization methods are often regarded as exploiting the local structure of the optimization landscape (for example, tunnelling across barriers<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 21\" title=\"Denchev, V. S. et al. What is the computational value of finite-range tunneling? Phys. Rev. X 6, 031015 (2016).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR21\" id=\"ref-link-section-d15498388e567\" rel=\"nofollow noopener\" target=\"_blank\">21<\/a>), our approach instead exploits the sparsity that is routinely present in the Fourier spectrum of the objective functions for combinatorial optimization problems, and it can also exploit more elaborate structure in the spectrum if present.<\/p>\n<p>Before presenting evidence that DQI can efficiently obtain approximate optima not achievable by known polynomial-time classical algorithms, we quickly illustrate the essence of the DQI algorithm by applying it to max-XORSAT. We use max-XORSAT as our first example because, although it is not the problem on which DQI has achieved its greatest success, it is the context in which DQI is simplest to explain.<\/p>\n<p>Given an m\u2009\u00d7\u2009n matrix B with m\u2009&gt;\u2009n, the max-XORSAT problem is to find an n-bit string x satisfying as many as possible of the m linear mod-2 equations Bx\u2009=\u2009v. As we are working modulo 2, we regard all entries of the matrix B and the vectors x and v as coming from the finite field \\({{\\mathbb{F}}}_{2}\\). The max-XORSAT problem can be rephrased as maximizing the objective function<\/p>\n<p>$$f({\\bf{x}})=\\mathop{\\sum }\\limits_{i=1}^{m}{(-1)}^{{v}_{i}+{{\\bf{b}}}_{i}\\cdot {\\bf{x}}},$$<\/p>\n<p>\n                    (1)\n                <\/p>\n<p>where bi is the ith row of B\u00a0and vi is the ith entry of v. Thus, f(x) is the number of the m linear equations that are satisfied minus the number unsatisfied.<\/p>\n<p>From equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Equ1\" rel=\"nofollow noopener\" target=\"_blank\">1<\/a>), one can see that the Hadamard transform of f is extremely sparse: it has m non-zero amplitudes, which are on the strings b1,\u00a0\u2026,\u00a0bm. The state \\({\\sum }_{{\\bf{x}}\\in {{\\mathbb{F}}}_{2}^{n}}f({\\bf{x}})| {\\bf{x}}\\rangle \\) is, thus, easy to prepare. Simply prepare the superposition \\({\\sum }_{i=1}^{m}{(-1)}^{{v}_{i}}| {{\\bf{b}}}_{i}\\rangle \\) and apply the quantum Hadamard transform. (Here, for simplicity, we have omitted normalization factors). Measuring the state \\({\\sum }_{{\\bf{x}}\\in {{\\mathbb{F}}}_{2}^{n}}f({\\bf{x}})| {\\bf{x}}\\rangle \\) in the computational basis yields a biased sample, where a string x is obtained with probability proportional to f(x)2, which slightly enhances the likelihood of obtaining strings with a large objective value relative to uniform random sampling.<\/p>\n<p>To obtain stronger enhancement, DQI prepares states of the form<\/p>\n<p>$$| P(f)\\rangle =\\sum _{{\\bf{x}}\\in {{\\mathbb{F}}}_{2}^{n}}P(f({\\bf{x}}))| {\\bf{x}}\\rangle ,$$<\/p>\n<p>\n                    (2)\n                <\/p>\n<p>where P is an appropriately normalized degree-\u2113 polynomial. The Hadamard transform of such a state always takes the form<\/p>\n<p>$$\\mathop{\\sum }\\limits_{k=0}^{{\\ell }}\\frac{{w}_{k}}{\\sqrt{\\left(\\begin{array}{c}m\\\\ k\\end{array}\\right)}}\\sum _{\\begin{array}{c}{\\bf{y}}\\in {{\\mathbb{F}}}_{2}^{m}\\\\ | {\\bf{y}}| =k\\end{array}}{(-1)}^{{\\bf{v}}\\cdot {\\bf{y}}}| {B}^{{\\rm{T}}}{\\bf{y}}\\rangle ,$$<\/p>\n<p>\n                    (3)\n                <\/p>\n<p>for some coefficients w0,\u00a0\u2026,\u00a0w\u2113. Here \u2223y\u2223 denotes the Hamming weight of the bit string y. The DQI algorithm prepares |P(f)\u27e9 in five steps. The first step is to prepare the superposition \\({\\sum }_{k=0}^{{\\ell }}{w}_{k}| {D}_{m,k}\\rangle \\), where<\/p>\n<p>$$| {D}_{m,k}\\rangle =\\frac{1}{\\sqrt{\\left(\\begin{array}{c}m\\\\ k\\end{array}\\right)}}\\sum _{\\begin{array}{c}{\\bf{y}}\\in {{\\mathbb{F}}}_{2}^{m}\\\\ | {\\bf{y}}| =k\\end{array}}| {\\bf{y}}\\rangle $$<\/p>\n<p>\n                    (4)\n                <\/p>\n<p>is the Dicke state of weight k. Preparing such superpositions over Dicke states can be done with \\({\\mathcal{O}}({m}^{2})\\) quantum gates using the techniques in refs. <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 22\" title=\"Bartschi, A. &amp; Eidenbenz, S. Short-depth circuits for Dicke state preparation. In Proc. 2022 IEEE International Conference on Quantum Computing and Engineering (QCE) (IEEE, 2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR22\" id=\"ref-link-section-d15498388e1740\" rel=\"nofollow noopener\" target=\"_blank\">22<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 23\" title=\"Wang, H., Tan, B., Cong, J. &amp; De Micheli, G. Quantum state preparation using an exact CNOT synthesis formulation. In Proc. Design, Automation and Test in Europe (DATE) 1&#x2013;6 (IEEE, 2024).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR23\" id=\"ref-link-section-d15498388e1743\" rel=\"nofollow noopener\" target=\"_blank\">23<\/a>. Second, the phase (\u22121)v\u22c5y is imposed by applying the product \\({Z}_{1}^{{v}_{1}}\\otimes \\ldots \\otimes {Z}_{m}^{{v}_{m}}\\), where Zm is the Pauli-Z operator acting on the mth qubit. Third, the quantity BTy is computed into an ancilla register using a reversible circuit for matrix multiplication. This yields the state<\/p>\n<p>$$\\mathop{\\sum }\\limits_{k=0}^{{\\ell }}\\frac{{w}_{k}}{\\sqrt{\\left(\\begin{array}{c}m\\\\ k\\end{array}\\right)}}\\sum _{\\begin{array}{c}{\\bf{y}}\\in {{\\mathbb{F}}}_{2}^{m}\\\\ | {\\bf{y}}| =k\\end{array}}{(-1)}^{{\\bf{v}}\\cdot {\\bf{y}}}| {\\bf{y}}\\rangle | {B}^{{\\rm{T}}}{\\bf{y}}\\rangle .$$<\/p>\n<p>\n                    (5)\n                <\/p>\n<p>The fourth step is to use the value BTy to infer y, which can then be subtracted from \\(| {\\bf{y}}\\rangle \\), thereby bringing it back to the all zeros state, which can be discarded. (This is known as \u2018uncomputation\u2019<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 24\" title=\"Nielsen, M. A. &amp; Chuang, I. L. Quantum Computation and Quantum Information (Cambridge Univ. Press, 2010).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR24\" id=\"ref-link-section-d15498388e2132\" rel=\"nofollow noopener\" target=\"_blank\">24<\/a>). The fifth and final step is to apply a Hadamard transform to the remaining register, yielding |P(f)\u27e9. This sequence of steps is illustrated in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Fig1\" rel=\"nofollow noopener\" target=\"_blank\">1<\/a>.<\/p>\n<p>Fig. 1: Schematic illustration of DQI.<a class=\"c-article-section__figure-link\" data-test=\"img-link\" data-track=\"click\" data-track-label=\"image\" data-track-action=\"view figure\" href=\"https:\/\/www.nature.com\/articles\/s41586-025-09527-5\/figures\/1\" rel=\"nofollow noopener\" target=\"_blank\"><img decoding=\"async\" aria-describedby=\"Fig1\" src=\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/41586_2025_9527_Fig1_HTML.png\" alt=\"figure 1\" loading=\"lazy\" width=\"685\" height=\"845\"\/><\/a><\/p>\n<p>As the initial Dicke state is of weight \u2113, the final polynomial P is of degree \u2113. Here, for simplicity, we take w\u2113\u2009=\u20091 and wk\u2009=\u20090 for all k\u2009\u2260\u2009\u2113. Recycling icon adapted from FreeSVG (<a href=\"https:\/\/freesvg.org\" rel=\"nofollow noopener\" target=\"_blank\">https:\/\/freesvg.org<\/a>) under a <a href=\"https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/\" rel=\"nofollow noopener\" target=\"_blank\">CC0 1.0<\/a> Universal Public Domain licence.<\/p>\n<p>The fourth step, in which |y\u27e9 is uncomputed, is not straightforward because B is a non-square matrix and, thus, inferring y from BTy is an underdetermined linear algebra problem. However, we also know that \u2223y\u2223\u2009\u2264\u2009\u2113. The problem of solving this underdetermined linear system with a Hamming weight constraint is precisely the syndrome decoding problem for the classical error-correcting code \\({C}^{\\perp }=\\{{\\bf{d}}\\in {{\\mathbb{F}}}_{2}^{m}:{B}^{{\\rm{T}}}{\\bf{d}}={\\bf{0}}\\}\\) with up to \u2113 errors.<\/p>\n<p>In general, syndrome decoding is an NP-hard problem<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 25\" title=\"Berlekamp, E., McEliece, R. &amp; van Tilborg, H. On the inherent intractability of certain coding problems. IEEE Trans. Inf. Theory 24, 384&#x2013;386 (1978).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR25\" id=\"ref-link-section-d15498388e2331\" rel=\"nofollow noopener\" target=\"_blank\">25<\/a>. However, when B is very sparse or has certain kinds of algebraic structure, the decoding problem can be solved by polynomial-time classical algorithms even when \u2113 is large (for example, linear in m). By solving this decoding problem using a reversible implementation of such a classical decoder, one uncomputes \\(| {\\bf{y}}\\rangle \\) in the first register. If the decoding algorithm requires T quantum gates, then the number of gates required to prepare |P(f)\u27e9 is \\({\\mathcal{O}}(T+{m}^{2})\\).<\/p>\n<p>Approximate solutions to the optimization problem are obtained by measuring |P(f)\u27e9 in the computational basis. The higher the degree of the polynomial in |P(f)\u27e9, the greater one can bias the measured bit strings towards solutions with a large objective value. However, this requires solving a harder decoding problem, as the maximum number of errors is equal to the degree of P. Next, we summarize how, by making an optimal choice of P and a judicious choice of decoder, DQI can be a powerful optimizer for some classes of problems.<\/p>\n<p>Although DQI can be applied more broadly, the most general optimization problem that we apply DQI to in this paper is max-LINSAT, which we define as follows.<\/p>\n<p>              Definition 1<\/p>\n<p>Let \\({{\\mathbb{F}}}_{p}\\) be a finite field and let \\(B\\in {{\\mathbb{F}}}_{p}^{m\\times n}\\). For each i\u2009=\u20091,\u00a0\u2026,\u00a0m, let \\({F}_{i}\\subset {{\\mathbb{F}}}_{p}\\) be an arbitrary subset of \\({{\\mathbb{F}}}_{p}\\), which yields a corresponding constraint \\({\\sum }_{j=1}^{n}{B}_{ij}{x}_{j}\\in {F}_{i}\\). The max-LINSAT problem is to find \\({\\bf{x}}\\in {{\\mathbb{F}}}_{p}^{n}\\) satisfying as many as possible of these m constraints.<\/p>\n<p>We focus primarily on the case that p has at most polynomially large magnitude and the subsets F1,\u00a0\u2026,\u00a0Fm are given as explicit lists. The max-XORSAT problem is the special case where p\u2009=\u20092 and \u2223Fi\u2223\u2009=\u20091 for all i.<\/p>\n<p>Consider a max-LINSAT instance where the sets F1,\u00a0\u2026,\u00a0Fm each have size r. Let \u27e8s\u27e9 be the expected number of constraints satisfied by the symbol string sampled in the final measurement of the DQI algorithm. Suppose we have a polynomial-time algorithm that can correct up to \u2113 bit flip errors on codewords from the code \\({C}^{\\perp }=\\{{\\bf{d}}\\in {{\\mathbb{F}}}_{p}^{m}:{B}^{{\\rm{T}}}{\\bf{d}}={\\bf{0}}\\}\\). Then, in polynomial time, DQI achieves the following approximate optimum to the max-LINSAT problem:<\/p>\n<p>$$\\frac{\\langle s\\rangle }{m}={\\left(\\sqrt{\\frac{{\\ell }}{m}\\left(1-\\frac{r}{p}\\right)}+\\sqrt{\\frac{r}{p}\\left(1-\\frac{{\\ell }}{m}\\right)}\\right)}^{2},$$<\/p>\n<p>\n                    (6)\n                <\/p>\n<p>if r\/p\u2009\u2264\u20091\u2009\u2212\u2009\u2113\/m and \u27e8s\u27e9\/m\u2009=\u20091 otherwise. See Supplementary Theorem\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">1.1<\/a> for the precise statement for perfect decoding and Supplementary Theorem\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">7.1<\/a> for the analogous statement in the presence of decoding errors. This is achieved by a specific optimal choice of the coefficients w0,\u00a0\u2026,\u00a0w\u2113, which can be classically precomputed in polynomial time, as described in Supplementary Information section <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>.<\/p>\n<p>Note that r\/p is the fraction of constraints that would be satisfied if the variables were assigned uniformly at random. When r\/p\u2009=\u20091\/2, equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Equ6\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>) becomes the equation of a semicircle. Hence, we informally refer to equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Equ6\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>) as the \u2018semicircle law\u2019.<\/p>\n<p>From equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Equ6\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>), any result on decoding a class of linear codes implies a corresponding result regarding the performance of DQI for solving a class of combinatorial optimization problems that are dual to these codes. This enables two new lines of research in quantum optimization. The first is to harvest the coding theory literature for rigorous theorems on the performance of decoders for various codes and obtain as corollaries guarantees on the approximation achieved by DQI for the corresponding optimization problems. The second is to perform computer experiments to determine the empirical performance of classical heuristic decoders, which, through equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Equ6\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>), can be compared against the empirical performance of classical heuristic optimizers. In this manner, DQI can be benchmarked instance-by-instance against classical heuristics, even for optimization problems far too large to attempt on present-day quantum hardware. We next describe our results so far from each of these two lines of research.<\/p>\n<p>We first use rigorous decoding guarantees to analyse the performance of DQI on the following problem.<\/p>\n<p>              Definition 2<\/p>\n<p>Given integers n\u2009&lt;\u2009p\u2009\u2212\u20091 with p prime, an instance of the optimal polynomial intersection (OPI) problem is as follows. Let F1,\u00a0\u2026,\u00a0Fp\u22121 be subsets of the finite field \\({{\\mathbb{F}}}_{p}\\). Find a polynomial \\(Q\\in {{\\mathbb{F}}}_{p}[y]\\) of degree at most n\u2009\u2212\u20091 that maximizes fOPI(Q)\u2009=\u2009\u2223{y\u2009\u2208\u2009{1, \u2026, p\u2009\u2212\u20091}: Q(y)\u2009\u2208\u2009Fy}\u2223, that is, that intersects as many of these subsets as possible.<\/p>\n<p>An illustration of this problem is given in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Fig2\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>.<\/p>\n<p>Fig. 2: Illustration of OPI problem.<a class=\"c-article-section__figure-link\" data-test=\"img-link\" data-track=\"click\" data-track-label=\"image\" data-track-action=\"view figure\" href=\"https:\/\/www.nature.com\/articles\/s41586-025-09527-5\/figures\/2\" rel=\"nofollow noopener\" target=\"_blank\"><img decoding=\"async\" aria-describedby=\"Fig2\" src=\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/41586_2025_9527_Fig2_HTML.png\" alt=\"figure 2\" loading=\"lazy\" width=\"685\" height=\"708\"\/><\/a><\/p>\n<p>A stylized example of the OPI problem. For \\({y}_{1}\\in {{\\mathbb{F}}}_{p}\\), the orange set above the point y1 represents \\({F}_{{y}_{1}}\\). Both polynomials Q1(y) and Q2(y) represent solutions that have a large objective value, as they each intersect all but one set Fy.<\/p>\n<p>In Supplementary Information section <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>, we show that OPI is a special case of max-LINSAT over \\({{\\mathbb{F}}}_{p}\\) with m\u2009=\u2009p\u2009\u2212\u20091 constraints in which B is a Vandermonde matrix and, thus, C\u22a5 is a Reed\u2013Solomon code. Syndrome decoding for Reed\u2013Solomon codes can be solved in polynomial time out to half the distance of the code, for example, using the Berlekamp\u2013Massey algorithm<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 26\" title=\"Berlekamp, E. R. Algebraic Coding Theory (revised edition) (World Scientific, 2015).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR26\" id=\"ref-link-section-d15498388e3443\" rel=\"nofollow noopener\" target=\"_blank\">26<\/a>. Consequently, in DQI we can take \u2113\u2009=\u2009\u230a(n\u2009+\u20091)\/2\u230b. For the regime where r\/p and n\/p are constants and p is taken asymptotically large, the fraction of satisfied constraints achieved by DQI using the Berlekamp\u2013Massey decoder can be obtained by substituting \u2113\/m\u2009=\u2009n\/2p into equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Equ6\" rel=\"nofollow noopener\" target=\"_blank\">6<\/a>).<\/p>\n<p>OPI and special cases of it have been studied in several domains. In the coding theory literature, OPI is studied under the name \u2018list-recovery\u2019, and in the cryptography literature it is studied under the name \u2018noisy polynomial reconstruction\/interpolation\u2019<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 27\" title=\"Naor, M. &amp; Pinkas, B. Oblivious transfer and polynomial evaluation. In Proc. 31st Annual ACM Symposium on Theory of Computing (STOC) 245&#x2013;254 (ACM, 1999).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR27\" id=\"ref-link-section-d15498388e3488\" rel=\"nofollow noopener\" target=\"_blank\">27<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Bleichenbacher, D. &amp; Nguyen, P. Q. Noisy polynomial interpolation and noisy Chinese remaindering. In Proc. International Conference on the Theory and Applications of Cryptographic Techniques (ed. Preneel, B.) 53&#x2013;69 (Springer, 2000).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR28\" id=\"ref-link-section-d15498388e3491\" rel=\"nofollow noopener\" target=\"_blank\">28<\/a>. OPI can also be viewed as a generalization of the polynomial approximation problem, studied in refs. <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Garcia-Morchon, O., Rietman, R., Shparlinski, I. E. &amp; Tolhuizen, L. Interpolation and approximation of polynomials in finite fields over a short interval from noisy values. Exp. Math. 23, 241&#x2013;260 (2014).\" href=\"#ref-CR29\" id=\"ref-link-section-d15498388e3495\">29<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Shparlinski, I. &amp; Winterhof, A. Noisy interpolation of sparse polynomials in finite fields. Appl. Algebra Eng. Commun. Comput. 16, 307&#x2013;317 (2005).\" href=\"#ref-CR30\" id=\"ref-link-section-d15498388e3495_1\">30<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"Shparlinski, I. E. Playing &#x2018;hide-and-seek&#x2019; with numbers. In Public-Key Cryptography: American Mathematical Society Short Course (2005).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR31\" id=\"ref-link-section-d15498388e3498\" rel=\"nofollow noopener\" target=\"_blank\">31<\/a>, in which each set Fi is a contiguous range of values in \\({{\\mathbb{F}}}_{p}\\). In Supplementary Information section <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">8<\/a>, we analyse the algorithms from these works in the literature and find that, for the parameter regime addressed by DQI, the best approximation achieved in polynomial time classically is 1\/2\u2009+\u2009n\/2p using Prange\u2019s algorithm. As shown in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Fig3\" rel=\"nofollow noopener\" target=\"_blank\">3<\/a>, for r\/p\u2009=\u20091\/2 and any fixed 0\u2009&lt;\u2009n\/p\u2009&lt;\u20091, DQI with the Berlekamp\u2013Massey decoder exceeds the satisfaction fraction achieved by Prange\u2019s algorithm in the limit of large p. Classically, the only methods we are aware of to exceed the satisfaction fraction achieved by Prange\u2019s algorithm are brute force search or slight refinements thereof, which have exponential runtime. Thus, DQI achieves a superpolynomial speed-up for this problem, assuming no polynomial-time algorithm is found that can match the satisfaction fraction that DQI achieves.<\/p>\n<p>Fig. 3: Approximate optima for OPI.<a class=\"c-article-section__figure-link\" data-test=\"img-link\" data-track=\"click\" data-track-label=\"image\" data-track-action=\"view figure\" href=\"https:\/\/www.nature.com\/articles\/s41586-025-09527-5\/figures\/3\" rel=\"nofollow noopener\" target=\"_blank\"><img decoding=\"async\" aria-describedby=\"Fig3\" src=\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/41586_2025_9527_Fig3_HTML.png\" alt=\"figure 3\" loading=\"lazy\" width=\"685\" height=\"726\"\/><\/a><\/p>\n<p>Plot of the expected fraction \u27e8s\u27e9\/p of satisfied constraints achieved by DQI with the Berlekamp\u2013Massey decoder and by Prange\u2019s algorithm for the OPI problem in the balanced case r\/p\u2009=\u20091\/2, as a function of the ratio of variables to constraints n\/p. At n\/p\u2009=\u20091\/10, Prange\u2019s algorithm satisfies a fraction 0.55 of the clauses whereas DQI satisfies \\(\\langle s\\rangle \/p=1\/2+\\sqrt{19}\/20\\approx 0.7179\\). As a concrete challenge to the classical algorithms community, we propose matching or exceeding this value in polynomial time. In our concrete resource estimation, we consider n\/p\u2009=\u20091\/2, where OPI achieves \\(\\langle s\\rangle \/p=1\/2+\\sqrt{3}\/4\\approx 0.9330\\) and Prange\u2019s algorithm achieves 0.75. BM, Berlekamp\u2013Massey decoder.<\/p>\n<p>At present, there are no results directly showing that the OPI problem in the parameter regime that we consider is classically intractable under any standard complexity-theoretic or cryptographic assumptions. However, such results are known for certain limiting cases of the OPI problem, and we propose the task of extending these results to regimes more relevant to DQI for future research. The hardness of the special case of OPI when \\(| \\,{f}_{i}^{-1}(\\,+1)| =1\\), in a certain parameter regime, has been proposed as a cryptographic assumption in ref. <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 32\" title=\"Naor, M. &amp; Pinkas, B. Oblivious polynomial evaluation. SIAM J. Comput. 35, 1254&#x2013;1281 (2006).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR32\" id=\"ref-link-section-d15498388e3793\" rel=\"nofollow noopener\" target=\"_blank\">32<\/a>, which has not been broken to our knowledge. Finding exact optima for OPI with \\(| \\,{f}_{i}^{-1}(\\,+1)| =1\\) can be cast as maximum-likelihood decoding for Reed\u2013Solomon codes, which is known to be NP-hard<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 33\" title=\"Guruswami, V. &amp; Vardy, A. Maximum-likelihood decoding of Reed-Solomon codes is NP-hard. IEEE Trans. Inf. Theory 51, 2249&#x2013;2256 (2005).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR33\" id=\"ref-link-section-d15498388e3856\" rel=\"nofollow noopener\" target=\"_blank\">33<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 34\" title=\"Gandikota, V., Ghazi, B. &amp; Grigorescu, E. NP-hardness of Reed-Solomon decoding, and the Prouhet-Tarry-Escott problem. SIAM J. Comput. 47, 1547&#x2013;1584 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR34\" id=\"ref-link-section-d15498388e3859\" rel=\"nofollow noopener\" target=\"_blank\">34<\/a>. Finding sufficiently good approximate optima is known to be as hard as discrete log<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 35\" title=\"Cheng, Q. &amp; Wan, D. On the list and bounded distance decodability of Reed-Solomon codes. SIAM J. Comput. 37, 195&#x2013;209 (2007).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR35\" id=\"ref-link-section-d15498388e3863\" rel=\"nofollow noopener\" target=\"_blank\">35<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 36\" title=\"Cheng, Q. &amp; Wan, D. Complexity of decoding positive-rate Reed-Solomon codes. In Proc. International Colloquium on Automata, Languages, and Programming (ICALP) (eds Aceto, L. et al.) 283&#x2013;293 (Springer, 2008).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR36\" id=\"ref-link-section-d15498388e3866\" rel=\"nofollow noopener\" target=\"_blank\">36<\/a>, but these hardness results do not match the parameter regime addressed by DQI.<\/p>\n<p>As a concrete example, for n\u2009\u2248\u2009p\/10 and r\/p\u2009\u2248\u20091\/2, the fraction of constraints satisfied by Prange\u2019s algorithm is 0.55, whereas DQI achieves \\(1\/2+\\sqrt{19}\/20\\approx 0.7179\\). As a specific point of comparison, we challenge the algorithms community to beat this with a classical polynomial-time algorithm. Interestingly, for these parameters, one statistically expects that solutions satisfying all p\u2009\u2212\u20091 constraints exist, but they apparently remain out of reach of polynomial-time algorithms both quantum and classical.<\/p>\n<p>To find classically intractable instances of OPI solvable by DQI with minimal quantum resources, we find it is advantageous to choose n\/p\u2009\u2248\u2009r\/p\u2009\u2248\u20091\/2. For these parameters, DQI achieves satisfaction fraction 0.933. As discussed in Supplementary Information section <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">13<\/a>, achieving this using classical algorithms known to us has a prohibitive computational cost for p as small as 521. The dominant cost in DQI plus the Berlekamp\u2013Massey decoder is the reversible implementation of the subroutine to find the shortest linear-feedback shift register used in the Berlekamp\u2013Massey algorithm. Using Qualtran<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 37\" title=\"Harrigan, M. P. et al. Expressing and analyzing quantum algorithms with Qualtran. Preprint at &#010;                https:\/\/arxiv.org\/abs\/2409.04643&#010;                &#010;               (2024).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR37\" id=\"ref-link-section-d15498388e3954\" rel=\"nofollow noopener\" target=\"_blank\">37<\/a>, we find that at p\u2009=\u2009521, the linear-feedback shift register can be found using approximately 1\u2009\u00d7\u2009108 logical Toffoli gates and 9\u2009\u00d7\u2009103 logical qubits.<\/p>\n<p>We next use computer experiments to benchmark the performance of DQI against classical heuristics on average-case instances from certain families of max-XORSAT with sparse B. DQI reduces such problems to decoding problems on codes with sparse parity-check matrices. Such codes are known as low-density parity-check (LDPC) codes. Polynomial-time classical algorithms, such as belief propagation, can decode randomly sampled LDPC codes up to numbers of errors that nearly saturate information-theoretic limits<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 3\" title=\"Richardson, T. J. &amp; Urbanke, R. L. The capacity of low-density parity-check codes under message-passing decoding. IEEE Trans. Inf. Theory 47, 599&#x2013;618 (2001).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR3\" id=\"ref-link-section-d15498388e3971\" rel=\"nofollow noopener\" target=\"_blank\">3<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 38\" title=\"Gallager, R. Low-density parity-check codes. IRE Trans. Inf. Theory 8, 21&#x2013;28 (1962).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR38\" id=\"ref-link-section-d15498388e3974\" rel=\"nofollow noopener\" target=\"_blank\">38<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 39\" title=\"M&#xE9;zard, M. &amp; Montanari, A. Information, Physics, and Computation (Oxford Univ. Press, 2009).\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#ref-CR39\" id=\"ref-link-section-d15498388e3977\" rel=\"nofollow noopener\" target=\"_blank\">39<\/a>. This makes sparse max-XORSAT an enticing target for DQI. Although we use max-XORSAT as a convenient test bed for DQI, other commonly studied optimization problems, such as max-k-SAT, could be addressed similarly. Specifically, consider any binary optimization problem in which the objective function counts the number of satisfied constraints, where each constraint is a Boolean function of at most k variables. By taking the Hadamard transform of the objective function, one converts such a problem into an instance of weighted max-k-XORSAT, where the number of variables is unchanged and the number of constraints has been increased by at most a factor of 2k.<\/p>\n<p>Although we are able to analyse the asymptotic average-case performance of DQI rigorously, we do not restrict the classical competition to algorithms with rigorous performance guarantees. Instead, we choose to set a high bar by also attempting to beat the empirical performance of classical heuristics that lack such guarantees.<\/p>\n<p>Through careful tuning of sparsity patterns in B, we are able to find some families of sparse max-XORSAT instances for which DQI with standard belief-propagation decoding finds solutions satisfying a larger fraction of constraints than we are able to find using a comparable number of computational steps by any of the general-purpose classical optimization heuristics that we tried, which are listed in Table <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"table anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#Tab1\" rel=\"nofollow noopener\" target=\"_blank\">1<\/a>. However, unlike our OPI example, we do not put this forth as a potential example of superpolynomial quantum advantage. Rather, we are able to construct a tailored classical algorithm specialized to these instances, which, with 7\u2009min of runtime, finds solutions where the fraction of constraints satisfied slightly beats DQI plus belief propagation (DQI\u2009+\u2009BP). As discussed in Supplementary Information section <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">9<\/a>, our tailored heuristic is a variant of simulated annealing that assigns temperature-dependent weights to the terms in the cost function determined by how many variables they contain.<\/p>\n<p>Table 1 Approximate optima for max-XORSAT<\/p>\n<p>The comparison against simulated annealing is complicated because, as shown in Supplementary Information section <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-025-09527-5#MOESM1\" rel=\"nofollow noopener\" target=\"_blank\">8.2<\/a>, the fraction of clauses satisfied by simulated annealing increases as a function of the duration of the anneal. Thus, there is not a unique sharply defined number indicating the maximum satisfaction fraction reachable by simulated annealing. DQI reduces our sparsity-tuned max-XORSAT problem to an LDPC decoding problem, which our implementation of belief propagation solves in approximately 8\u2009s on a single core, excluding the time used to load and parse the instance. Thus, a natural point of comparison is the result obtained by simulated annealing with a similar runtime. By running our optimized C++ implementation of simulated annealing for 8\u2009s, we are only able to reach 0.764. If we allow the parallel execution of several anneals and increase our runtime allowance, we are able to eventually replicate the satisfaction fraction achieved by DQI\u2009+\u2009BP using simulated annealing. The shortest anneal that achieved this used five cores and ran for 73\u2009h, which is five orders of magnitude longer than our belief-propagation decoder. Although this is dependent on the implementation details, we can take this ratio of runtimes as a rough indicator of the ratio of computational steps. In the context of DQI, the decoder would need to be implemented as a reversible circuit and subject to an overhead due to quantum error correction, so this should not be interpreted as an indicator of the quantum versus the classical runtime.<\/p>\n","protected":false},"excerpt":{"rendered":"NP-hardness results indicate that finding exact optima and even sufficiently good approximate optima for worst-case instances of many&hellip;\n","protected":false},"author":2,"featured_media":244114,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[19944,1159,1160,199,12506,79],"class_list":{"0":"post-244113","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-computer-science","9":"tag-humanities-and-social-sciences","10":"tag-multidisciplinary","11":"tag-physics","12":"tag-quantum-information","13":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/244113","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=244113"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/244113\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/244114"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=244113"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=244113"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=244113"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}