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Roger Colbeck + Renato Renner :: Free RANDOMNESS can be amplified (2012, Nature Physics) -
May 23, 2012
"Are there fundamentally random processes in nature? Theoretical predictions, confirmed experimentally, such as the violation of Bell inequalities, point to an affirmative answer. However, these results are based on the assumption that measurement settings can be chosen freely at random, so assume the existence of perfectly free random processes from the outset. Here we consider a scenario in which this assumption is weakened and show that partially free random bits can be amplified to make arbitrarily free ones. Given a source of random bits whose correlation with other variables is below a certain threshold, we propose a procedure for generating fresh random bits that are virtually uncorrelated with all other variables. We also conjecture that such procedures exist for any non-trivial threshold. Our result is based solely on the no-signalling principle, which is necessary for the existence of free randomness." -
"The scientists now made use of entanglement and locality -- the fact that for example a local event on Earth does not exert any direct influence on another planet -- to show that beyond a certain point "weakly" indeterministic situations can be amplified to such an extent that they are completely random. This is achievable for example with two entangled quantum particles that are strongly coupled but are then measured independently of one another. The scientists' calculations showed that the quantum correlation between the bits can be so strong that they cannot be correlated with anything existing previously. This means that the results are completely random, whereas only weak randomness is needed for the choice of the measurement." -
"The two scientists stress that they have not thereby proved that the world is non-deterministic. However, they say there is nothing in between. The existence of weak randomness automatically implies that there must be an unlimited amount of strong randomness. However, Colbeck says it is first of all necessary to achieve a particular "randomness threshold": "Our method allows randomness to be amplified once a certain threshold has been reached. It would now be interesting to know whether this threshold can be made arbitrarily small by using improved methods." This would then mean that an arbitrarily small amount of indetermisism would be sufficient to generate an unlimited amount of randomness."
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