A tossed coin is the simplest source of randomness. But if the coin is shaved, it starts cheating. In the quantum world, light plays the role of the coin: its properties are fundamentally unpredictable. The catch is that the device that “flips” the quantum coin might be faulty or even swapped by an adversary.
The authors built a generator that does not require full trust in its components. It suffices to limit the energy of the emitted light states, as if we ensured the coin is not too heavy. Then, even with a partially broken device, randomness is preserved. The setup operates at 100 megahertz and produces 1.165 megabits of random numbers per second after post-processing.
Such a generator is useful for quantum cryptography — a field where random numbers serve as locks for secret messages. The stronger the lock, the harder it is to break into correspondence. The new approach relaxes hardware requirements while maintaining high speed and resistance to attacks.
Quantum random number generators are already used in lotteries and casinos, where fairness is critical.