  Quantumkey distribution (QKD) promises unconditional security for
communication. However, the random choices of the measurement basis in QKD
usually result in low key creation efficiency. This drawback is overcome in the
differential-phase-shift QKD, provided that each photon can be prepared in a
large number of time bins with a proper waveform. In this work we develop a
miniature 1550-nm single-photon source to generate narrowband single photon in
50 time bins with a nearly optimal waveform for achieving unity key creation
efficiency. By utilizing these single photons in the field test, we demonstrate
the differential-phase-shift QKD with a key creation efficiency of 97%. Our
work shows that the practical QKD can benefit from the narrowband single
photons with controllable waveforms.
