Onset of Superactivation of Quantum Capacity
Marco Parentin
Onset of Superactivation of Quantum Capacity.
Rel. Riccardo Adami. Politecnico di Torino, Corso di laurea magistrale in Quantum Engineering, 2025
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Abstract
In quantum information theory, the quantum capacity of a channel is a measure of its ability to reliably transmit quantum information. In 2008, Smith and Yard demonstrated the striking phenomenon of superactivation, where two quantum channels — each individually incapable of transmitting quantum information — can exhibit a strictly positive quantum capacity when used in tandem. While superactivation has been studied extensively in the asymptotic, memoryless setting, its behavior in the case of a finite number of uses of these channels is yet to be explored. The purpose of this thesis is to investigate superactivation in this setting, exploring the minimum number of channel uses required to send quantum information reliably and hence determine the resources needed to observe this phenomenon in practice.
Leveraging the Choi representation of quantum channels, this work exploits semidefinite programming techniques to obtain lower bounds on the optimal rate of information transmission over a finite number of uses of two known zero-capacity channels
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