Abstract
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.
Highlights
Quantum communications promises reliable transmission of quantum information, efficient distribution of entanglement and generation of completely secure keys
As already mentioned in the Introduction, we establish the two-way capacities (Q2, D2 and K) for a number of quantum channels at both finite and infinite dimension, that is, we consider channels defined on both discrete variable (DV) and continuous variable (CV) systems[2]
Two-way capacities are benchmarks for quantum repeaters because they are derived by removing any technical limitation from the point-topoint protocols between the remote parties, who may perform the most general strategies allowed by quantum mechanics in the absence of pre-shared entanglement
Summary
Quantum communications promises reliable transmission of quantum information, efficient distribution of entanglement and generation of completely secure keys. Quantum information is more fragile than its classical counterpart, so that the ideal performances of quantum protocols may rapidly degrade in realistic practical implementations This is a basic limitation that affects any point-to-point protocol of quantum communication over a quantum channel, where two remote parties transmit qubits, distribute entanglement or secret keys. We devise a general methodology that completely simplifies the study of adaptive protocols and allows us to upperbound the two-way capacities of an arbitrary quantum channel with a computable single-letter quantity In this way, we are able to establish exact formulas for the two-way capacities of several fundamental channels, such as bosonic lossy channels, quantum-limited amplifiers, dephasing and erasure channels in arbitrary dimension. We upperbound the two-way capacities of any quantum channel, with closed formulas proven for bosonic Gaussian channels[2], Pauli channels, erasure channels and amplitude damping channels[1]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
