  A higher-order (HO) symmetry-protected topological (SPT) state can be
realized in a plaquette-modulated square lattice antiferromagnet, which hosts a
spin-$1/2$ degenerate mode on each corner of the lattice with open boundaries.
In this work, we show with the field-theoretic analysis and quantum Monte Carlo
simulations that the plaquette modulation can drive a direct topological
quantum phase transition from the HOSPT to a trivial disordered phase across
the deconfined quantum critical point (DQCP) between the antiferromagnetic (AF)
order and the valence bond solid (VBS) order, thus the DQCP is a multicritical
point bridging both the AF-VBS transition and the topological transition of the
HOSPT phase. Our work thus reveals the ubiquitous duality between topological
transitions of SPT phases and DQCPs.
