  Non-reciprocal photonic devices are essential components of classical optical
information processing. It is interesting and important to investigate their
feasibility in the quantum world. In this work, the quantum properties of an
on-chip silicon nitride (SiN)-based magneto-optical (MO) isolator were studied
using a single-photon non-reciprocal dynamical transmission experiment. The
measured isolation ratio for single photons achieved was 12.33 dB, which proved
the functionality of our on-chip isolator. The quantum coherence of the passing
single photons was further verified using high-visibility quantum interference.
Our work will promote on-chip isolators within the integrated quantum circuits
and help introduce novel phenomena in quantum information processes.
