Entanglement swapping in critical quantum spin chains

The transfer of quantum information between many-qubit states is a subject of fundamental importance in quantum science and technology. We consider entanglement swapping in critical quantum spin chains, where the entanglement between the two chains is induced solely by the Bell-state measurements. We employ a boundary conformal field theory (CFT) approach and describe the measurements as conformal boundary conditions in the replicated field theory. We show that the swapped entanglement exhibits a logarithmic scaling, whose coefficient takes a universal value determined by the scaling dimension of the boundary condition changing operator. We apply our framework to the critical spin-$\frac{1}{2}$ XXZ chain and determine the universal coefficient by the boundary CFT analysis. We also numerically verify these results by the tensor-network calculations. Possible experimental relevance to Rydberg atom arrays is briefly discussed.