Wave-Shape-Tolerant Photonic Quantum Gates

Photons, acting as "flying qubits" in propagation geometries such as waveguides, appear unavoidably in the form of wave packets (pulses). The actual shape of the photonic wave packet as well as possible temporal and spectral correlations between the photons play a critical role in successful scalable computation. Currently, unentangled indistinguishable photons are considered a suitable resource for scalable photonic circuits. Here we show that using so-called coherent photon conversion, it is possible to construct flying-qubit gates which are not only insensitive to wave shapes of the photons and temporal and spectral correlations between them but which also fully preserve these wave shapes and correlations upon the processing. This allows the use of photons with correlations and purity in a very broad range for a scalable computation. Moreover, such gates can process entangled photonic wave packets even more effectively than unentangled ones.