  Quantum key distribution (QKD) enables unconditionally secure communication
ensured by the laws of physics, opening a promising route to security
infrastructure for the coming age of quantum computers. QKD's demonstrated
secret-key rates (SKRs), however, fall far short of the gigabit-per-second
rates of classical communication, hindering QKD's widespread deployment. QKD's
low SKRs are largely due to existing single-photon-based protocols'
vulnerability to channel loss. Floodlight QKD (FL-QKD) boosts SKR by
transmitting many photons per encoding, while offering security against
collective attacks. Here, we report an FL-QKD experiment operating at a 1.3
Gbit/s SKR over a 10-dB-loss channel. To the best of our knowledge, this is the
first QKD demonstration that achieves a gigabit-per-second-class SKR,
representing a critical advance toward high-rate QKD at metropolitan-area
distances.
