44 research outputs found
Entanglement between random and clean quantum spin chains
The entanglement entropy in clean, as well as in random quantum spin chains
has a logarithmic size-dependence at the critical point. Here, we study the
entanglement of composite systems that consist of a clean and a random part,
both being critical. In the composite, antiferromagnetic XX-chain with a sharp
interface, the entropy is found to grow in a double-logarithmic fashion , where is the length of the chain. We have also
considered an extended defect at the interface, where the disorder penetrates
into the homogeneous region in such a way that the strength of disorder decays
with the distance from the contact point as . For
, the entropy scales as , while for , when the extended interface defect
is an irrelevant perturbation, we recover the double-logarithmic scaling. These
results are explained through strong-disorder RG arguments.Comment: 12 pages, 7 figures, Invited contribution to the Festschrift of John
Cardy's 70th birthda