Quantum non-signalling assisted zero-error classical capacity of qubit channels

In this paper, we explicitly evaluate the one-shot quantum non-signalling assisted zero-error classical capacities M 0 for qubit channels. In particular, we show that for nonunital qubit channels, M QNS 0 = 1, which implies that in the one-shot setting, nonunital qubit channels cannot transmit any information with zero probability of error even when assisted by quantum non-signalling correlations. Furthermore, we show that for qubit channels, M 0 equals to the one-shot entanglementassisted zero-error classical capacities. This means that for a single use of a qubit channel, quantum non-signalling correlations are not more powerful than shared entanglement.