  By using the infinite time-evolving block decimation, we study quantum
fidelity and entanglement entropy in the spin-1/2 Heisenberg alternating chain
under an external magnetic field. The effects of the magnetic field on the
fidelity are investigated, and its relation with the quantum phase transition
(QPT) is analyzed. The phase diagram of the model is given accordingly, which
supports the Haldane phase, the singlet-dimer phase, the Luttinger liquid phase
and the paramagnetic phase. The scaling of entanglement entropy in the gapless
Luttinger liquid phase is studied, and the central charge c = 1 is obtained. We
also study the relationship between the quantum coherence, string order
parameter and QPTs. Results obtained from these quantum information
observations are consistent with the previous reports.
