Generic nonadditivity of quantum capacity in simple channels

02/16/2022
by   Felix Leditzky, et al.
0

Determining capacities of quantum channels is a fundamental question in quantum information theory. Despite having rigorous coding theorems quantifying the flow of information across quantum channels, their capacities are poorly understood due to super-additivity effects. Studying these phenomena is important for deepening our understanding of quantum information, yet simple and clean examples of super-additive channels are scarce. Here we study a simple family of qutrit channels called the platypus channel, and show that it exhibits super-additivity of coherent information when used jointly with a variety of qubit channels. A higher-dimensional variant of the platypus channel displays super-additivity of quantum capacity together with an erasure channel. Subject to the "spin-alignment conjecture" introduced in a companion paper, our results on super-additivity of quantum capacity extend to lower-dimensional channels as well as larger parameter ranges. In particular, super-additivity occurs between two weakly additive channels each with large capacity on their own, in stark contrast to previous results. Remarkably, a single, novel transmission strategy achieves super-additivity in all examples. Our results show that super-additivity is much more prevalent than previously thought. It can occur across a wide variety of channels, even when both participating channels have large quantum capacity.

READ FULL TEXT

page 1

page 2

page 3

page 4

research
02/16/2022

The platypus of the quantum channel zoo

Understanding quantum channels and the strange behavior of their capacit...
research
05/01/2023

Noise is resource-contextual in quantum communication

Estimating the information transmission capability of a quantum channel ...
research
01/24/2023

The superadditivity effects of quantum capacity decrease with the dimension for qudit depolarizing channels

Quantum channel capacity is a fundamental quantity in order to understan...
research
07/01/2021

Coherent information of a quantum channel or its complement is generically positive

The task of determining whether a given quantum channel has positive cap...
research
05/13/2021

Detecting positive quantum capacities of quantum channels

Using elementary techniques from analytic perturbation theory of Hermiti...
research
12/14/2017

Secret Message Transmission over Quantum Channels under Adversarial Quantum Noise: Secrecy Capacity and Super-Activation

We determine the secrecy capacities of arbitrarily varying quantum chann...
research
05/19/2023

Concrete Quantum Channels and Algebraic Structure of Abstract Quantum Channels

Construction and testing of preconditioners of Toeplitz/block Toeplitz m...

Please sign up or login with your details

Forgot password? Click here to reset