  The beam-splitter (BS) is one of the most common and important components in
modern optics, and lossless BS which features unitary transformation induces
Hermitian evolution of light. However, the practical BS based on the conversion
between different degree of freedoms are naturally non-Hermitian, as a result
of essentially open quantum dynamics. In this work, we experimentally
demonstrate a non-Hermitian BS for the interference between traveling photonic
and localized magnonic modes. The non-Hermitian magnon-photon BS is achieved by
the coherent and incoherent interaction mediated by the excited levels of
atoms, which is reconfigurable by adjusting the detuning of excitation.
Unconventional correlated interference pattern is observed at the photon and
magnon output ports. Our work is potential for extending to single-quantum
level to realize interference between a single photon and magnon, which
provides an efficient and simple platform for future tests of non-Hermitian
quantum physics.
