Loophole-Free Bell Test Achieved at Delft

Hensen et al. at Delft University of Technology perform the first loophole-free Bell test using electron spins in nitrogen-vacancy centers in diamond separated by 1.3 km, detecting a Bell parameter S = 2.42 ± 0.20. The experiment simultaneously closes both the detection loophole and the locality loophole, definitively ruling out local hidden variable theories and earning Nature's 2015 breakthrough of the year.