Covert Capacity of Bosonic Channels

We investigate the quantum-secure covert-communication capabilities of lossy thermal-noise bosonic channels, the quantum-mechanical model for many practical channels. We determine the expressions for the covert capacity of these channels: Lno-EA, when Alice and Bob share only a classical secret, and LEA, when they benefit from entanglement assistance. We find that entanglement assistance alters the fundamental scaling law for covert communication. Instead of Lno-EAn-rno-EA(n), rno-EA(n)=o(n), entanglement assistance allows LEAnlogn-rEA(n), rEA(n)=o(nlogn), covert bits to be transmitted reliably over n channel uses.