Explicit restricted isometries with $k=m^{2/3-o(1)}$

arXiv:2611.14475v1 Announce Type: cross Abstract: We construct an explicit family of real $m\times n$ restricted isometries with $m\to\infty$, $m/n\to 0$, $\delta_k\to 0$, and $k=m^{2/3-o(1)}$. We combine Gershgorin's circle theorem with a flat RIP estimate to reduce the problem to choosing a large vertex set in a strongly regular graph with the property that every small subset spans few edges. We select this vertex set using an incidence geometric result due to Zahl. The proof only uses the entrywise absolute value of the Gram matrix despite the conventional wisdom that such proof techniques exhibit a barrier of $m^{1/2}$. We prove that this barrier is actually $m^{2/3}$, and we show that our particular construction exhibits the same barrier.