  We demonstrate an invertible all-optical gate on chip, with the roles of
control and signal switchable by slightly adjusting their relative arrival time
at the gate. It is based on quantum Zeno blockade driven by sum-frequency
generation in a periodic-poled lithium niobate microring resonator. For two
nearly-identical nanosecond pulses, the later arriving pulse is modulated by
the earlier arriving one, resulting in 2.4 and 3.9 power extinction between the
two, respectively, when their peak power is 1 mW and 2 mW. Our results, while
to be improved and enriched, herald a new paradigm of logical gates and
circuits for exotic applications.
