Short answer: A quantum random number generator draws random bits from quantum measurement outcomes, and "source-independent" designs aim to stay secure even when the light source is not trusted. A 2020 Physical Review X paper reports a generator using a completely untrusted photonic source at 8.05 Gb/s, a source-device-independent photonic design reports 4 Mbps, and a more recent continuous-variable design uses vacuum fluctuations. These are laboratory demonstrations, and each authors' security claim rests on their stated model.

What source-independent means

The 2020 paper explains that certain quantum measurement outcomes are unpredictable to all possible observers, and that such events can be used to generate numbers whose randomness is asserted from the underlying physics. It says the central challenge is to rigorously quantify how much of the entropy produced by a real device is intrinsically unpredictable. It describes partially device-independent designs, which are independent of the measurement devices or of the source, but need detailed characterization of the rest.

2020: an untrusted source

The Oxford-led team formally introduces, designs and experimentally demonstrates an ultrafast optical quantum random number generator that uses a totally untrusted photonic source. Considering completely general quantum attacks, they certify and generate random numbers in real time at 8.05 Gb/s with a composable security parameter of 10 to the minus 10. They explain that composable security means a protocol stays secure even if arbitrarily combined with other instances of itself or other protocols, and say this is the fastest generation of composably secure quantum random numbers reported.

Photon-pair timing

A photonics paper in Advanced Photonics proposes and demonstrates a source-device-independent generator that gives true random bits with an untrusted source. Bits come from measuring the arrival time of either photon of time-energy entangled photon pairs from spontaneous parametric downconversion, with the entanglement verified through nonlocal dispersion cancellation. The authors extract a generation rate of 4 Mbps using a modified entropic uncertainty relation, and say this can be improved to gigabits per second with advanced single-photon detectors. That improvement is a projection.

Vacuum fluctuations

A more recent paper in Quantum Science and Technology presents a high-speed continuous-variable generator based on heterodyne detection of vacuum fluctuations, following a source-device-independent security model in which entropy comes from measurement uncertainty and no model of the source is needed. Security depends only on the trusted measurement device and the calibrated discretization. The authors digitize the outputs with a 12-bit converter sampling at 3.2 GS/s per channel, run Toeplitz hashing on a field-programmable gate array, and report that the output passes standard statistical test suites. The sustained generation rate is not legible in the text available here, so none is given.

Limits

"Source-independent" removes the need to trust the source, but the measurement device remains trusted in the continuous-variable design. Passing statistical tests does not by itself prove security. The photon-pair design's rate is 4 Mbps as measured.

FAQ

What does untrusted source mean?

The 2020 paper certifies randomness while treating the photonic source as completely untrusted.

How fast was the 2020 generator?

8.05 Gb/s with a composable security parameter of 10 to the minus 10, according to the authors.

How are bits made in the photon-pair design?

By measuring the arrival time of either photon in time-energy entangled pairs, with entanglement checked through nonlocal dispersion cancellation.

What is trusted in the vacuum-noise design?

The measurement device and the calibrated discretization.

Are these in commercial use?

None of the three papers describes a product.

All field notes