  Most quantum key distribution (QKD) protocols can be classified as either a
discrete-variable (DV) protocol or continuous-variable (CV) protocol, based on
how classical information is being encoded. We propose a protocol that combines
the best of both worlds -- the simplicity of quantum state preparation in
DV-QKD together with the cost-effective and high-bandwidth of homodyne
detectors used in CV-QKD. Our proposed protocol has two highly practical
features: (1) it does not require the honest parties to share the same
reference phase (as required in CV-QKD) and (2) the selection of decoding basis
can be performed after measurement. We also prove the security of the proposed
protocol in the asymptotic limit under the assumption of collective attacks.
Our simulation suggests that the protocol is suitable for secure and high-speed
practical key distribution over metropolitan distances.
