Prompted by a comment from a reader, we have noticed a flaw in our arguments (in the form of an asymmetry between the roles of Bob and Alice in the protocol) as presented in our published paper [1]. As a result, we re-derived our calculations and detected a nontrivial error. Correcting this error requires a modification of the phase error rate, which causes a violation of the starting assumptions. To avoid misleading readers and the academic community, we would like to retract our paper.

The original paper was published 17 March 2020 and was retracted on 17 June 2020.