  Random number generation is an enabling technology for fields as varied as
Monte Carlo simulations and quantum information science. An important
application is a secure quantum key distribution (QKD) system; here, we propose
and demonstrate an approach to random number generation that satisfies the
specific requirements for QKD. In our scheme, vacuum fluctuations of the
electromagnetic-field inside a laser cavity are sampled in a discrete manner in
time and amplified by injecting current pulses into the laser. Random numbers
can be obtained by interfering the laser pulses with another independent laser
operating at the same frequency. Using only off-the-shelf opto-electronics and
fibre-optics components at 1.5 $\mu$m wavelength, we experimentally demonstrate
the generation of high-quality random bits at a rate of up to 1.5 GHz. Our
results show the potential of the new scheme for practical information
processing applications.
