  Since the introduction of the decoy-state technique, phase-randomised weak
coherent light pulses have been the key to increase the practicality of
quantum-based communications. Their ultra-fast generation was accomplished via
compact gain-switched (GS) lasers, leading to high key rates in quantum key
distribution (QKD). Recently, the question arose of whether the same laser
could be employed to achieve high-speed measurement-device-independent-QKD, a
scheme that promises long-haul quantum communications immune to all detector
attacks. For that, a challenging highvisibility interference between
independent picosecond optical pulses is required. Here, we answer the above
question in the affirmative by demonstrating high-visibility interference from
two independent GS lasers triggered at 1GHz. The result is obtained through a
careful characterization of the laser frequency chirp and time jitter. By
relating these quantities to the interference visibility, we obtain a
parameter-free verification of the experimental data and a numerical simulation
of the achievable key rates. These findings are beneficial to other
applications making use of GS lasers, including random number generation and
standard QKD.
