  Today, almost all information processing is performed using electronic logic
circuits operating with up to several gigahertz frequency. All-optical logic,
however, that holds the promise to allow up to three orders of magnitude higher
speed [1] has not been able to provide a viable alternative because approaches
that had been tried were either not scalable, not energy efficient or did not
show a significant speed benefit. Whereas essential all-optical transistor
functionalities have been already demonstrated across a range of platforms
[2-4], using them to implement the complete Boolean logic gate set and in
particular negation - switching off an optical signal with another optical
signal - poses a major challenge [5]. Here, we realize a universal NOR logic
gate by introducing the concept of non-ground-state dynamic exciton-polariton
condensation in an organic semiconductor microcavity under non-resonant pulsed
excitation. In the presence of either of the input signals inserted at opposite
in-plane momenta, non-ground state dynamic condensation supersedes spontaneous
ground-state condensation, resulting in a NOR-operator output signal within
less than a picosecond. An additional optical transistor, fed by the output of
the NOR gate, is then used to regenerate the output signal such that it is
usable as input for cascading gates, a prerequisite for scale up. Our results
constitute an essential step towards the realization of more complex logic
optical circuitry that could boost future information processing applications.
