Quantum Randomness: New Insights from Chinese Scientists

Researchers at the University of Science and Technology of China (USTC) have made a significant discovery regarding quantum randomness. Published in *Physical Review Letters*, their study reveals that not all forms of quantum nonlocality ensure intrinsic randomness, particularly in complex systems. The team demonstrated that while violating two-input Bell inequalities guarantees randomness certification, this principle falters in multiple-input, multiple-output (MIMO) systems. They found that certain Bell inequalities, like facet inequalities, can show nonlocality without ensuring randomness. However, Salavrakos-Augusiak-Tura-Wittek-Acín-Pironio (SATWAP) inequalities consistently link nonlocality and randomness, even in MIMO setups. Experiments using high-dimensional photonic systems validated these findings. The SATWAP inequality proved effective in certifying randomness, achieving a rate of 1.867 bits per photon pair in a four-dimensional system. This highlights the importance of selecting appropriate Bell inequalities for randomness certification in high-dimensional systems. The sensitivity of SATWAP inequalities makes them a powerful tool, even with imperfect detection efficiency, broadening the scope for practical applications like secure random number generation.