Multi-dimensional memory in sheared granular materials

TL;DR

This study investigates how two-dimensional hydrogel sphere packings can remember multiple types of shear deformations, revealing that memories are learned as paths through phase space rather than single values.

Contribution

It demonstrates that granular materials can encode and recall multiple shear memories as learned paths, influenced by deformation order and type.

Findings

Memory depends on deformation type and order

Memories are learned as paths in phase space

Readout reveals cusp at training strain

Abstract

To explore what features of multi-dimensional training can be remembered in granular materials, the response of a small, two-dimensional packing of hydrogel spheres to two independent types of shear is measured. Packings are trained via the application of several identical shear cycles, either of a single shear type or combinations of the two types. The memory is then read out using a standard protocol capable of revealing memories as a cusp at the point where readout reaches the training strain. The ability to read out a memory is sensitive not only to the type of deformation applied but also to the order in which different types of training are performed. These results underscore the importance of thinking of memories not as single remembered value (amplitude) but as a learned path through phase space.