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In this paper, we present exact exponential algorithms for computing branchwidth that are fast both in theory and in practice. The running times of these algorithms are single-exponential in the number of vertices. Our basic algorithm is…

Data Structures and Algorithms · Computer Science 2026-05-19 Taiki Kaneda , Yasuaki Kobayashi , Hisao Tamaki

We introduce a novel quantum algorithm for similar subgraph identification in form of an NP-hard cardinality-constrained binary quadratic optimization problem. Given a weighted reference graph with Laplacian $\boldsymbol{B}$, our algorithm…

Quantum Physics · Physics 2026-04-03 Ruben Kara , Sven Danz , Tobias Stollenwerk , Andrea Benigni

Several `edge-discovery' applications over graph-based data models are known to have worst-case quadratic time complexity in the nodes, even if the discovered edges are sparse. One example is the generic link discovery problem between two…

Artificial Intelligence · Computer Science 2017-07-04 Mayank Kejriwal

In graph theory, the longest path problem is the problem of finding a simple path of maximum length in a given graph. For some small classes of graphs, the problem can be solved in polynomial time [2, 4], but it remains NP-hard on general…

Data Structures and Algorithms · Computer Science 2014-09-15 Lajos L. Pongrácz

A dynamic graph algorithm is a data structure that answers queries about a property of the current graph while supporting graph modifications such as edge insertions and deletions. Prior work has shown strong conditional lower bounds for…

Data Structures and Algorithms · Computer Science 2023-01-30 Monika Henzinger , Ami Paz , A. R. Sricharan

The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise quantum walks have shown much potential as a frame- work for developing new quantum algorithms.…

Berry and Wang [Phys. Rev. A {\bf 83}, 042317 (2011)] show numerically that a discrete-time quantum random walk of two noninteracting particles is able to distinguish some non-isomorphic strongly regular graphs from the same family. Here we…

Quantum Physics · Physics 2013-08-27 Kenneth Rudinger , John King Gamble , Eric Bach , Mark Friesen , Robert Joynt , S. N. Coppersmith

Quantum walks on graphs have shown prioritized benefits and applications in wide areas. In some scenarios, however, it may be more natural and accurate to mandate high-order relationships for hypergraphs, due to the density of information…

Quantum Physics · Physics 2017-09-26 Ying Liu , Jiabin Yuan , Bojia Duan , Dan Li

With the explosive growth of graph-structured data, graph databases have become a critical infrastructure for supporting large-scale and complex data analysis. Among various graph operations, shortest distance queries play a fundamental…

Cryptography and Security · Computer Science 2026-03-30 Xuemei Fu

Spectral partitioning is a simple, nearly-linear time, algorithm to find sparse cuts, and the Cheeger inequalities provide a worst-case guarantee for the quality of the approximation found by the algorithm. Local graph partitioning…

Data Structures and Algorithms · Computer Science 2012-11-07 Shayan Oveis Gharan , Luca Trevisan

We study the problem of efficiently refuting the k-colorability of a graph, or equivalently certifying a lower bound on its chromatic number. We give formal evidence of average-case computational hardness for this problem in sparse random…

Computational Complexity · Computer Science 2020-08-28 Afonso S. Bandeira , Jess Banks , Dmitriy Kunisky , Cristopher Moore , Alexander S. Wein

Recently, Apers and Piddock [TQC '23] strengthened the connection between quantum walks and electrical networks via Kirchhoff's Law and Ohm's Law. In this work, we develop a new multidimensional electrical network by defining Alternative…

Quantum Physics · Physics 2025-05-27 Jianqiang Li , Sebastian Zur

The graph isomorphism problem looks deceptively simple, but although polynomial-time algorithms exist for certain types of graphs such as planar graphs and graphs with bounded degree or eigenvalue multiplicity, its complexity class is still…

Discrete Mathematics · Computer Science 2025-07-11 Stefan Klus , Patrick Gelß

Given a graph, the densest subgraph problem asks for a set of vertices such that the average degree among these vertices is maximized. Densest subgraph has numerous applications in learning, e.g., community detection in social networks,…

Cryptography and Security · Computer Science 2022-11-15 Alireza Farhadi , MohammadTaghi Hajiaghayi , Elaine Shi

The most general examples of quantum learning advantages involve data labeled by cryptographic or intrinsically quantum functions, where classical learners are limited by the infeasibility of evaluating the labeling functions using…

Quantum Physics · Physics 2026-02-19 Riccardo Molteni , Simon C. Marshall , Vedran Dunjko

Continuous-time quantum walks provide a natural framework to tackle the fundamental problem of finding a node among a set of marked nodes in a graph, known as spatial search. Whether spatial search by continuous-time quantum walk provides a…

Quantum Physics · Physics 2022-10-24 Simon Apers , Shantanav Chakraborty , Leonardo Novo , Jérémie Roland

Graph states are a class of multi-partite entangled quantum states that are ubiquitous in quantum information. We study equivalence relations between graph states under local unitaries (LU) to obtain distinguishing methods both in local and…

Quantum Physics · Physics 2025-06-12 Lina Vandré , Jarn de Jong , Frederik Hahn , Adam Burchardt , Otfried Gühne , Anna Pappa

We study the average probability that a discrete-time quantum walk finds a marked vertex on a graph. We first show that, for a regular graph, the spectrum of the transition matrix is determined by the weighted adjacency matrix of an…

Combinatorics · Mathematics 2021-08-24 Hanmeng Zhan

Quantum networks are important for quantum communication, enabling tasks such as quantum teleportation, quantum key distribution, quantum sensing, and quantum error correction, often utilizing graph states, a specific class of multipartite…

Quantum Physics · Physics 2025-11-19 Aniruddha Sen , Kenneth Goodenough , Don Towsley

Quantum walks underlie an important class of quantum computing algorithms, and represent promising approaches in various simulations and practical applications. Here we design stroboscopically monitored quantum walks and their subsequent…

Quantum Physics · Physics 2022-09-27 Quancheng Liu , David A. Kessler , Eli Barkai