  Randomness is a fundamental feature of quantum mechanics, which is an
invaluable resource for both classical and quantum technologies. Practical
quantum random number generators (QRNG) usually need to trust their devices,
but their security can be jeopardized in case of imperfections or malicious
external actions. In this work, we present a robust implementation of a
Semi-Device-Independent QRNG that guarantees both security and fast generation
rates. The system works in a prepare and measure scenario where measurement and
source are untrusted, but a bound on the energy of the prepared states is
assumed. Our implementation exploits heterodyne detection, which offers
increased generation rate and improved long-term stability compared to
alternative measurement strategies. In particular, due to the tomographic
properties of heterodyne measurement, we can compensate for fast phase
fluctuations via post-processing, avoiding complex active phase stabilization
systems. As a result, our scheme combines high security and speed with a simple
setup featuring only commercial-off-the-shelf components, making it an
attractive solution in many practical scenarios.
