Event Operators and Quantum Gates

Relativistic quantum information (RQI) is an emerging field of research dedicated to investigating quantum information protocols in a relativistic setting. Such models may give us clues about what sort of features a proper theory of quantum gravity ought to have. In this paper, we consider what happens to a quantum circuit operating in a curved spacetime background. We model the circuit using quantum optics in a Schwarzchild metric, with qubits constructed from single photons. The result is compared to an alternative model using 'event operators' in place of regular quantum optics. In this new model, field operators acting at different events in the photon's history are made to commute with each other; a requirement that has elsewhere been shown to remove paradoxes from situations where closed time-like curves are involved. Our comparison of the models reveals that the event operator model is inherently non-linear, although it gives the same predictions as normal quantum optics in most cases.