  At the fundamental level, quantum communication is ultimately limited by
noise. For instance, quantum signals cannot be amplified without the
introduction of noise in the amplified states. Furthermore, photon loss reduces
the signal-to-noise ratio, accentuating the effect of noise. Thus, most of the
efforts in quantum communications have been directed towards overcoming noise
to achieve longer communication distances, larger secret key rates, or to
operate in noisier environmental conditions. Here, we propose and
experimentally demonstrate a platform for quantum communication based on
ultrafast optical techniques. In particular, our scheme enables the
experimental realization of high-rates and quantum signal filtering approaching
a single spectro-temporal mode, resulting in a dramatic reduction in channel
noise. By experimentally realizing a 1-ps optically induced temporal gate, we
show that ultrafast time filtering can result in an improvement in noise
tolerance by a factor of up to 1200 compared to a 2-ns electronic filter
enabling daytime quantum key distribution or quantum communication in bright
fibers.
