  We propose an application of a parity-time symmetric non-Hermitian
Su-Schrieffer-Heeger (SSH) model by embedded it in a two-dimensional square
lattice tube. The coalescence state at the exceptional point of non-Hermitian
SSH model is chiral and selectively controls helical transport and
amplification. Two typical helicity-dependent scattering dynamics are observed.
If the incidence has an identical helicity with the embedded non-Hermitian SSH
model, we observe a perfect transmission without reflection. However, if the
incidence has an opposite helicity with the embedded non-Hermitian SSH model,
except for a full transmission, we observe an amplified transmission with
different helicity from the incidence; but the amplified reflection has
identical helicity with the incidence. These intriguing features are completely
unexpected in Hermitian system. Moreover, the helical amplification at high
efficiency can be triggered by an arbitrary excitation. The different dynamics
between incidences with opposite helicities are results of unidirectional
tunneling, which is revealed to be capable of realizing without introducing
magnetic field. Our findings open a direction in all-optical device and provide
perspectives in non-Hermitian transport.
