ETH Zurich entangles qubits across tunnel to certify randomness
ETH Zurich entangled two superconducting qubits across a 30-meter tunnel and used a two-source extractor to produce random numbers certified by quantum physics, published in Nature.
A team at ETH Zurich led by cryptographer Renato Renner entangled two superconducting qubits separated by about 30 meters and generated random bit streams that the authors say are certified by quantum physics. The work appears in the journal Nature.
The qubits were connected by microwave photons sent through a tunnel on the university campus. Measurements on each qubit produced correlated outcomes consistent with entanglement while individual measurement results remained unpredictable.
The researchers processed the raw measurement results with a two-source extractor. That method combines two weakly random inputs and converts them into outputs the paper describes as provably random under quantum theory and the specific experimental setup.
The experiment builds on tests of quantum nonlocality and Bell inequalities, which exclude local hidden variables as a way to deterministically set outcomes. The team designed the experiment and the data processing to close relevant loopholes; the paper states the generated bits are unpredictable even to an adversary with detailed knowledge of the devices.
The authors identify applications that require high-quality randomness. They list uses in cryptography such as key generation, secure boot processes and hardware security modules, and they note potential uses in gaming and lotteries. The paper notes that cost and scaling constraints could affect adoption.
The hardware used superconducting qubits and a controlled microwave link in a dedicated tunnel. The paper outlines engineering challenges for scaling the system to serve large numbers of users and for operating in different environments.
The authors also address requirements for deployment in security systems, including standards, supply chains and methods to audit and verify the entropy source.
Renato Renner led the research project. The paper presents the result as a form of certified entropy grounded in quantum theory and the experimental design and suggests the finding could influence how organizations source randomness.
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