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2017 ; 8
(ä): 15043
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Fundamental limits of repeaterless quantum communications
#MMPMID28443624
Pirandola S
; Laurenza R
; Ottaviani C
; Banchi L
Nat Commun
2017[Apr]; 8
(ä): 15043
PMID28443624
show ga
Quantum communications promises reliable transmission of quantum information,
efficient distribution of entanglement and generation of completely secure keys.
For all these tasks, we need to determine the optimal point-to-point rates that
are achievable by two remote parties at the ends of a quantum channel, without
restrictions on their local operations and classical communication, which can be
unlimited and two-way. These two-way assisted capacities represent the ultimate
rates that are reachable without quantum repeaters. Here, by constructing an
upper bound based on the relative entropy of entanglement and devising a
dimension-independent technique dubbed 'teleportation stretching', we establish
these capacities for many fundamental channels, namely bosonic lossy channels,
quantum-limited amplifiers, dephasing and erasure channels in arbitrary
dimension. In particular, we exactly determine the fundamental rate-loss tradeoff
affecting any protocol of quantum key distribution. Our findings set the limits
of point-to-point quantum communications and provide precise and general
benchmarks for quantum repeaters.