  We propose a scheme to realize parity-time (PT) symmetry via
electromagnetically induced transparency (EIT). The system we consider is an
ensemble of cold four-level atoms with an EIT core. We show that the
cross-phase modulation contributed by an assisted field, the optical lattice
potential provided by a far-detuned laser field, and the optical gain resulted
from an incoherent pumping can be used to construct a PT-symmetric complex
optical potential for probe field propagation in a controllable way. Comparing
with previous study, the present scheme uses only a single atomic species and
hence is easy for the physical realization of PT-symmetric Hamiltonian via
atomic coherence.
