Addendum to: Nature Physics, published online 6 April 2018.

The Nature Article on which this News & Views article is based was retracted on 8 March 2021 (see H. Zhang et al. Retraction Note: Quantized Majorana conductance. Nature 591, E30; 2021). Accordingly, any reference in the News & Views article to the Zhang et al. paper and the results therein, in particular the reported conductance quantization, should be disregarded. That said, the discussion in the News & Views article about what Majorana zero modes are and how quantized conductance might be an important piece of evidence for their existence remains correct.