From Ramanujan graphs to Ramanujan complexes. (24th January 2020)

• Record Type: Journal Article
• Authors: Lubotzky, Alexander; Parzanchevski, Ori
• Is Part Of: Philosophical transactions. Volume 378:Number 2163(2020)
• Publication Date: 2020-01-24
• Subjects: graphs -- Ramanujan -- complexes; Physical sciences -- Periodicals; Engineering -- Periodicals; Mathematics -- Periodicals; 500
• DOI: 10.1098/rsta.2018.0445
• Languages: English
• ISSNs: 1364-503X

Abstract

Abstract : Ramanujan graphs are graphs whose spectrum is bounded optimally. Such graphs have found numerous applications in combinatorics and computer science. In recent years, a high-dimensional theory has emerged. In this paper, these developments are surveyed. After explaining their connection to the Ramanujan conjecture, we will present some old and new results with an emphasis on random walks on these discrete objects and on the Euclidean spheres. The latter lead to 'golden gates' which are of importance in quantum computation. This article is part of a discussion meeting issue 'Srinivasa Ramanujan: in celebration of the centenary of his election as FRS'.