Entanglement and boundary critical phenomena

Abstract

We investigate boundary critical phenomena from a quantum-information perspective. Bipartite entanglement in the ground state of one-dimensional quantum systems is quantified using the R\'enyi entropy ${S}_{\ensuremath{\alpha}}$, which includes the von Neumann entropy $(\ensuremath{\alpha}\ensuremath{\rightarrow}1)$ and the single-copy entanglement $(\ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\infty})$ as special cases. We identify the contribution of the boundaries to the R\'enyi entropy, and show that there is an entanglement loss along boundary renormalization group (RG) flows. This property, which is intimately related to the Affleck-Ludwig $g$ theorem, is a consequence of majorization relations between the spectra of the reduced density matrix along the boundary RG flows. We also point out that the bulk contribution to the single-copy entanglement is half of that to the von Neumann entropy, whereas the boundary contribution is the same.