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A Quantum Random Number Generator

Random number sequences are needed for data encryption and other critical uses – yet truly random numbers are nearly impossible to come by. All classical processes such as coin flips are, in principle, predictable. But one thing that absolutely cannot be predicted is the value resulting from a measurement of a quantum object.

And even then, the object must be certified to be in a purely quantum state by a process known as a Bell inequality test. PFC-supported researchers created precisely such a system by generating “entanglement” (a quantum condition in which the states of two objects become inextricably interdependent) between two ions and then confirming their entanglement by a Bell test. The test involves changing the relative orientation of the ions and the detectors that monitor photons emitted from each ion. If the emitted photons are correlated in a certain ratio, then the system is certified as purely quantum-mechanical.

Of course, if the system is truly quantum-mechanical, then the measurements are guaranteed to be random by the laws of physics. The measurements can then be used to generate a long string of random numbers. In a proof-of-principle experiment reported in Nature, the team produced a sequence of 42 numbers that was absolutely unique to that particular experiment. That is, the results were not only genuinely random, but also genuinely private. The findings may lead to development of future practical quantum-mechanical random-number generators  for use in data security, Monte Carlo simulations and other applications.


A. Acin, S. Massar, A. Boyer de la Giroday, D. N. Matsukevich, P. Maunz, S. Olmschenk, D. Hayes, L. Luo, T. A. Manning and C. Monroe
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