On-chip implementation of the probabilistic quantum optical state comparison amplifier

The transmission distance of quantum optical signals is limited by propagation losses in transmission media, since conventional optical amplification schemes cannot be used as the copying of an arbitrary and unknown quantum state is forbidden. One strategy to offset propagation loss is the use of probabilistic, or non-deterministic, amplification schemes, one example of which is the state comparison amplifier. We report an implementation of a state comparison amplifier that substitutes a fiber-coupled femtosecond laser-written waveguide chip in place of standard fiber-coupled bulk optical components. This pathfinder on-chip implementation of the quantum amplifier has resulted in several performance improvements: the polarization integrity of the written waveguides has resulted in improved visibility of the amplifier interferometers; the potential of substantially-reduced losses throughout the amplifier configuration; and a more compact and environmentally-stable amplifier which is scalable to more complex networks.