Eberhardt's inequality and recent loophole-free experiments

Abstract

Recent experiments using innovative optical detectors and techniques have strongly increased the capacity of testing the violation of the Bell's inequalities in the Nature. Most of them have used the Eberhardt's inequality (EI) to close the "detection" loophole. Closing the "locality" loophole has been attempted by space-like separated detections and fast and random changes in the setting of the bases of observation. Also, pulsed pumping and time stamped data to close the "time-coincidence" loophole, and sophisticated statistical methods to close the "memory" loophole, have been used. In this paper, the meaning of the EI is reviewed. A simple hidden-variables theory based on a relaxation of the condition of "measurement independence", which was devised long ago for the Clauser-Horne-Shimony and Holt inequality, is adapted to the EI case. It is used here to evaluate the significance of the results of the new experiments, which are briefly described. A Table summarizes the main results.