  Phase-randomized optical homodyne detection is a well-known technique for
performing quantum state tomography. So far, it has been mainly considered a
sophisticated tool for laboratory experiments but unsuitable for practical
applications. In this work, we change the perspective and employ this technique
to set up a practical continuous-variable quantum random number generator. We
exploit a phase-randomized local oscillator realized with a gain-switched laser
to bound the min-entropy and extract true randomness from a completely
uncharacterized input, potentially controlled by a malicious adversary. Our
proof-of-principle implementation achieves an equivalent rate of 270 Mbit/s. In
contrast to other source-device-independent quantum random number generators,
the one presented herein does not require additional active optical components,
thus representing a viable solution for future compact, modulator-free,
certified generators of randomness.
