  Recent advances in non-Hermitian physical systems have led to numerous novel
optical phenomena and applications. However, most realizations are limited to
classical systems and quantum fluctuations of light is unexplored. For the
first time, we report the observation of quantum correlations between light
channels in an anti-symmetric optical system made of flying atoms. Two distant
optical channels coupled dissipatively, display gain, phase sensitivity and
quantum correlations with each other, even under linear atom-light interaction
within each channel. We found that quantum correlations emerge in the phase
unbroken regime and disappears after crossing the exceptional point. Our
microscopic model considering quantum noise evolution produces results in good
qualitative agreement with experimental observations. This work opens up a new
direction of experimental quantum nonlinear optics using non-Hermitian systems,
and demonstrates the viability of nonlinear coupling with linear systems by
using atomic motion as feedback.
