  Random numbers are essential for applications ranging from secure
communications to numerical simulation and quantitative finance. Algorithms can
rapidly produce pseudo-random outcomes, series of numbers that mimic most
properties of true random numbers while quantum random number generators
(QRNGs) exploit intrinsic quantum randomness to produce true random numbers.
Single-photon QRNGs are conceptually simple but produce few random bits per
detection. In contrast, vacuum fluctuations are a vast resource for QRNGs: they
are broad-band and thus can encode many random bits per second. Direct
recording of vacuum fluctuations is possible, but requires shot-noise-limited
detectors, at the cost of bandwidth. We demonstrate efficient conversion of
vacuum fluctuations to true random bits using optical amplification of vacuum
and interferometry. Using commercially-available optical components we
demonstrate a QRNG at a bit rate of 1.11 Gbps. The proposed scheme has the
potential to be extended to 10 Gbps and even up to 100 Gbps by taking advantage
of high speed modulation sources and detectors for optical fiber
telecommunication devices.
