  A continuous-variable quantum key distribution protocol based on squeezed
states and heterodyne detection is introduced and shown to attain higher secret
key rates over a noisy line than any other one-way Gaussian protocol. This
increased resistance to channel noise can be understood as resulting from
purposely adding noise to the signal that is converted into the secret key.
This notion of noise-enhanced tolerance to noise also provides a better
physical insight into the poorly understood discrepancies between the
previously defined families of Gaussian protocols.
