Quantum Capacity of Partially Corrupted Quantum Network

Abstract

We discuss a quantum network, in which the sender has $m_0$ outgoing channels, the receiver has $m_0$ incoming channels, each channel is of capacity $d$, each intermediate node applies invertible unitary, only $m_1$ channels are corrupted, and other non-corrupted channels are noiseless. As our result, we show that the quantum capacity is not smaller than $(m_0-2m_1+1)\log d$ under the following two settings. In the first case, the unitaries on intermediate nodes are arbitrary and the corruptions on the $m_1$ channels are individual. In the second case, the unitaries on intermediate nodes are restricted to Clifford operations and the corruptions on the $m_1$ channels are adaptive, i.e., the attacker is allowed to have a quantum memory. Further, our code in the second case realizes the noiseless communication even with the single-shot setting and is constructed dependently only on the network topology and the places of the $m_1$ corrupted channels while this result holds regardless of the network topology and the places.