Date: March 9, 2026
Time: 3:45-5 p.m.
Location: Computing and Information Science Building, Room 450 or Click here to attend via Zoom
Speaker: Rachel Zhang, MIT
Abstract: In this talk, I will describe our construction of the first explicit lossless vertex expanders. These are d-regular graphs where every small set S of vertices has (1-eps)d|S| distinct neighbors, which is (nearly) the maximal possible permitted by the degree. Previously, the strongest known explicit vertex expanders were those given by Ramanujan graphs, whose spectral properties imply that every small set S of vertices has 0.5d|S| distinct neighbors. Based on joint work with Jun-Ting Hsieh, Ting-Chun Lin, Alex Lubotzky, Sidhanth Mohanty, Ryan O'Donnell, and Assaf Reiner.
Bio: Rachel is a fifth year Ph.D. student in EECS at MIT, advised by Yael Kalai and Vinod Vaikuntanathan. She enjoys thinking about error-correcting codes and expander graphs. Her work has received a Best Paper Award at FOCS 2025, and Best Student Paper Awards at STOC 2022 and ITCS 2025.