Activation of quantum capacity of Gaussian channels

TL;DR

This paper demonstrates that certain Gaussian channels with zero quantum capacity can activate and enhance the capacity of other noisy channels, including those with previously unknown capacities, with implications for realistic communication systems.

Contribution

It shows activation of quantum capacity in Gaussian channels using specific positive-partial-transpose channels, including cases with unknown capacities, expanding understanding of quantum communication noise mitigation.

Findings

Activation of quantum capacity confirmed for Gaussian lossy channels.

Activation also occurs in Gaussian thermal attenuators with previously unknown capacities.

Supports the use of channel activation for improving realistic quantum communication systems.

Abstract

Quantum channels can be activated by a kind of channels whose quantum capacity is zero. This activation effect might be useful to overcome noise of channels by attaching other channels which can enhance the capacity of a given channel. In this work, we show that such an activation is possible by specific positive-partial-transpose channels for Gaussian lossy channels whose quantum capacities are known. We also test more general case involving Gaussian thermal attenuator whose the exact value of quantum capacity has been unknown so far. For a recently suggested narrow upper bound on quantum capacity of the thermal attenuator, we confirm the fact that an activation of quantum capacity occurs as well. This result is applicable for realistic situations in which Gaussian channels describe the noises of communication systems.