  In comparison to qubit-based protocols, qudit-based quantum key distribution
(QKD) ones gen- erally allow two cooperative parties to share unconditionally
secure keys under a higher channel noise. However, it is very hard to prepare
and measure the required quantum states in qudit-based protocols in general.
One exception is the recently proposed highly error tolerant qudit-based proto-
col known as the Chau15 [1]. Remarkably, the state preparation and measurement
in this protocol can be done relatively easily since the required states are
phase encoded almost like the diagonal basis states of a qubit. Here we report
the first proof-of-principle demonstration of the Chau15 protocol. One
highlight of our experiment is that its post-processing is based on practical
one-way manner, while the original proposal in Ref. [1] relies on complicated
two-way post-processing, which is a great challenge in experiment. In addition,
by manipulating time-bin qudit and measurement with a variable delay
interferometer, our realization is extensible to qudit with high-dimensionality
and confirms the experimental feasibility of the Chau15 protocol.
