Semi-device-independent quantum random number generator based on homodyne detection

A system for providing a semi-device-independent random output signal, the system comprising:

• a laser source for providing respective coherent laser signals of a same optical mode in a signal arm and a local oscillator arm between a quantum signal source, Alice, and at a quantum signal detector, Bob;
• a trusted random seed for Alice and Bob randomly selecting operation in a test mode or a randomness generation mode for each of n rounds;
• wherein, if the test mode is chosen:
• Alice is configured to prepare a coherent test state of the laser signal in the signal arm uniformly chosen from a set of test states for transmission to Bob;
• and
• Bob is configured to measure the test state using a phase modulator in the local oscillator arm and a homodyne detector comprising a balanced beam splitter for the signal arm and the local oscillator arm and selects a bit value bi depending on the measurement result;
• and wherein, if the randomness generation mode is chosen:
• Alice is configured to prepare a coherent default state of the laser signal in the signal arm for transmission to Bob;
• and
• Bob is configured to measure the coherent default state using the phase modulator in the local oscillator arm and the homodyne detector in the opposite observable compared to an X- or P-quadrature alignment of the coherent default state and selects respective bit values bi depending on the measurement result;
• and further wherein
• the system is configured to generate a raw random string from bit values bi of rounds in which randomness generation mode was chosen, and to use rounds in which test mode was chosen to estimate an entropy of the raw random string.