Correlations across channel uses can improve quantum communication rates, making optimization over arbitrarily large blocks a central difficulty in determining quantum capacity. We show how full permutation invariance limits this advantage for every finite-dimensional memoryless channel. The optimized coherent informat...
Z. Khanian, Debbie W. Leung, Graeme Smith· 0 citations
We study collective state preparation and channel encoding in fermionic systems under parity superselection and composition governed by the canonical anticommutation relations. For a two-mode Gaussian state $\tau$, we obtain the exact entanglement of formation, $E_{\mathrm F}^{\mathrm{phys}}(\tau^{\otimes m})=\lceil m/...
Farzin Salek, Amir-Reza Negari, Graeme Smith et al.· 0 citations
We study the transmission of two independent confidential classical messages over a quantum broadcast channel, one for each receiver. Each message must remain secret from the other receiver, including when that receiver knows its own message. For classical inputs and quantum outputs, we establish the classical Marton-t...
Paula Belzig, S. Ghosal, Farzin Salek et al.· 0 citations
Entanglement is monogamous: if it is shared among more than two parties, the entanglement between any pair cannot be very strong. For an integer $k\geq 2$, $k$-extendibility of a state $\rho_{AB}$ quantifies this as the number of copies of $B$ that can be simulated by the state's environment. We introduce fractional ex...
R. G. Ahmed, Graeme Smith· 0 citations
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