Experimental tests of Lieb–Robinson bounds

Abstract

Judging by the enormous body of work that it has inspired, Elliott Lieb and Derek Robinson’s 1972 article on the “Finite group velocity of quantum spin systems” can be regarded as a high-impact paper, as research accountants say. But for more than 30 years, this major contribution to quantum physics has remained pretty much confidential. Lieb and Robinson’s work eventually found a large audience in the years 2000, with the rapid and concomitant development of quantum information theory and new experimental platforms. In this chapter, I will first remind the reader of the central result of Lieb and Robinson’s work, which is the emergence of a local causality structure in the dynamics of non-relativistic quantum systems, and manifests by the exponential suppression of the commutator of any two operators outside an effective light cone in space-time. I will then review the experiments that most closely relate to this finding, in the sense that they reveal the group velocity of information propagation in “real” quantum systems. Finally, as an outlook, I will attempt to make a connection with the quantum version of the butterfly effect recently studied in chaotic quantum systems.