Physicists achieve ‘perfect randomness’ in breakthrough quantum experiment

Researchers at ETH Zurich have demonstrated a means of generating “perfect randomness” by using entangled superconducting qubits.

Creating true randomness is extremely difficult. Even the most sophisticated conventional random number generator can carry tiny biases. While in most everyday uses those biases are harmless, in cryptography — where the security of encrypted systems depends on unpredictability — even the most subtle pattern can become an exploitable weakness.

The team at ETH Zurich, led by physics professors Renato Renner and Andreas Wallraff, say they have shown how to overcome this flaw and create perfectly random numbers using quantum physics, a milestone they describe as the first certified realization of perfect randomness.

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The experiment revolves around two superconducting chips cooled to temperatures near absolute zero. Each chip acts as a qubit, the quantum equivalent of a binary bit. The chips are connected by a 98-foot (30-meter) tube that is also supercooled, allowing microwave photons to shuttle between them and create entanglement — a “spooky” quantum state where two particles can become linked such that measuring one instantly affects the other.

By keeping the qubits nearly 100 feet apart, the researchers ensured that, during measurement, even light-speed signals could not travel between the qubits quickly enough to influence the outcome. In the language of quantum physics, that helps preserve the integrity of the entanglement and prevents unwanted communication from spoiling the randomness.

The team then started with an imperfect random-number generator to choose the measurement basis for the qubits. After the quantum measurement, they used a special algorithm to amplify the randomness in the results. The key idea is that the quantum system can cleanse the input of bias and produce an output sequence of zeros and ones that is certifiably random, meaning its randomness is not merely assumed or inferred from standard statistical tests.

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Andreas Wallraff and Renato Renner next to the 100-foot link connecting two quantum chips.

(Image credit: Kilian Kessler / ETH Zurich)

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