Entanglement equipartition in critical random spin chains

Quantum many-body systems naturally present intricate entanglement patterns between the extensive number of degrees of freedom. In the presence of symmetry, the entanglement contribution of each symmetry sector gives a powerful lens through which to observe these patterns, both in theory and in experiment. It has been proposed that, in clean systems, an entanglement equipartition generically emerges, meaning that the different sectors contribute equally. This work shows that such equipartition is, not obviously, robust against disorder, at least in the random singlet phase of quantum spin chains. Furthermore, the authors identify the subleading term breaking the equipartition.