  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 Renyi entropy S_alpha, which includes
the von Neumann entropy (alpha=1) and the single-copy entanglement
(alpha=infinity) as special cases. We identify the contribution from the
boundary entropy to the Renyi 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, can be regarded as 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.
