Standard super-activation for Gaussian channels requires squeezing

Abstract

The quantum capacity of bosonic Gaussian quantum channels can be non-additive in a particularly striking way: a pair of such optical-fiber type channels can individually have zero quantum capacity but super-activate each other such that the combined channel has strictly positive capacity. This has been shown in [Nature Photonics 5, 624 (2011)] where it was conjectured that squeezing is a necessary resource for this phenomenon. We provide a proof of this conjecture by showing that for gauge covariant channels a Choi matrix with positive partial transpose implies that the channel is entanglement-breaking. In addition, we construct an example which shows that this implication fails to hold for Gaussian channels which arise from passive interactions with a squeezed environment.

5 pages, close to published version

References in corpus (5)

• Gaussian Quantum Information
• Quantum Communication With Zero-Capacity Channels
• Multi-mode bosonic Gaussian channels
• Not-so-normal mode decomposition
• Detecting Incapacity

Cited by in corpus (9)

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• Process output nonclassicality and nonclassicality depth of quantum-optical channels
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• Quantum-optical channels that output only classical states
• Entanglement Thresholds of Doubly-Parametric Quantum Transducers
• How Deep the Theory of Quantum Communications Goes: Superadditivity, Superactivation and Causal Activation
• On quantum additive Gaussian noise channels