Dynamics of quantum avalanches in 1D disordered spin chains

Recent studies have questioned the stability of the many-body localized (MBL) phase in one-dimensional disordered spin chains in the thermodynamic limit. Thermalization in this limit is thought to be due to "quantum avalanches", in which rare Griffiths regions of lower disorder serve as thermalizing baths. These regions, which are sure to exist in the thermodynamic limit, are rare by nature and thus to observe their effect one either needs to access very large system sizes or resort to biased sampling. In this talk we present evidence of avalanches in numerical studies using the latter, and show these systems are unstable at disorder much larger than commonly believed.