  High-dimensional quantum key distribution (HD-QKD) allows two parties to
generate multiple secure bits of information per detected photon. In this work,
we show that decoy state protocols can be practically implemented for HD-QKD
using only one or two decoy states. HD-QKD with two decoy states, under
realistic experimental constraints, can generate multiple secure bits per
coincidence at distances over 200 km and at rates similar to those achieved by
a protocol with infinite decoy states. Furthermore, HD-QKD with only one decoy
state is practical at short distances, where it is almost as secure as a
protocol with two decoy states. HD-QKD with only one or two decoy states can
therefore be implemented to optimize the rate of secure quantum communications.
