An integrated quantum random noise source includes a substrate, an optical oscillator that may be integral to the substrate coupled by an optical waveguide to an optical directional coupler. The optical directional coupler has two outputs that are coupled by optical waveguides to a pair of photodetectors that are part of a balanced photodetector. The balanced photodetector in response outputs an analogue signal proportional to the difference in photocurrents of the two photodetectors. The analogue output signal from the balanced photodetector is a random Gaussian-distributed signal representative of quadrature measurements on the quantum vacuum state of light. The random noise source can be coupled other apparatus to provide a source of random bits.