Study Of Freedom-of-choice Loophole In Loophole-free Bell Experiment

Beginning with the debate between Einstein and Boer,the nonlocality of quantum mechanics has attracted the attention of scientists.In 1935,Einstein et al.proposed EPR paradox,and about 30 years later Bell proposed the inequality,which had a great influence on the nonlocality test of quantum mechanics.Up to now,almost all the results of Bell inequality test have verified the existence of nonlocality in the quantum world.However,this does not give a perfect end to the nonlocality test of quantum mechanics.In the Bell test experiments,due to the imperfect factors of the experimental device and the detection means,these experimental results are established under the premise of many hypotheses.These hypotheses introduce experimental loopholes,which lead to the experimental results cannot completely eliminate the influence of the local hidden variable,so that the classical local realism can still explain the experimental results.With the development of technology,scientists have become interested in the loophole-free Bell test.Highefficiency and highfidelity entanglement sources,as well as almost perfect singlephoton detection techniques,make it possible to implement loophole-free Bell test.After Hensen et al.first realized the loophole-free Bell test experiment in 2015,a series of loophole-free Bell test experiment were proposed.However,most of the experiments have closed detection loophole and locality loophole,and there is still no substantial advances in the challenging freedomofchoice loophole.In order to close the freedomofchoice loophole,scientists proposed to use the cosmic random number to control the selection of measurement basis in the Bell test experiments,which can reject local hidden variable mechanisms deep into the cosmic history.For the first time,we have realized random number generation based on the arrival time of cosmic photons,and use this random number to successfully implement the Bell test that not only close the locality and detection loopholes simultaneously,but also test the null hypothesis against local hidden variable mechanisms for events that took place 11 years ago.In addition,the freedomofchoice loophole stems from the fact that random numbers in experiments are not really random,random numbers may be affected by local hidden variables and thus there is an unknown correlations.Scientists have proposed to use human "free will" to generate random numbers,thus break the correlations between random numbers and between random numbers and entangled photons.In this paper,we mainly describe the following two aspects of using cosmic random number to address the freedomofchoice loophole in Bell test experiments:1.We experimentally realize random number generation based on the arrival time of cosmic photons,and test the randomness of the random number.Furthermore,we demonstrate the feasibility of applying this random number to loophole-free Bell test experiments.2.Utilizing the randomness in cosmic photons from pairs of stars on the opposite sides of the sky for the measurement setting choices,we perform a null hypothesis test that rejects local hidden variable models taking place as early as 11 years before the experiment with high confidence.