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Tesi etd-09232018-233830


Thesis type
Tesi di laurea magistrale
Author
CHESSA, STEFANO
URN
etd-09232018-233830
Title
Quantum Communication via Spin Networks
Struttura
FISICA
Corso di studi
FISICA
Commissione
relatore Giovannetti, Vittorio
Parole chiave
  • Spin Systems
  • Quantum Spin Networks
  • Quantum Communication
Data inizio appello
17/10/2018;
Consultabilità
completa
Riassunto analitico
The advent of Quantum Mechanics offered a new paradigm by which physicists were able to describe the behaviour of physical systems at the microscopic scale, opening the way to the discovery of a wide amount of
peculiar phenomena and applications.
One of these is Quantum Information, which describes how quantum effects in quantum systems affect our ability to produce, store, transfer information and more in general how to approach some physical problems from an "informational" point of view.
This work is placed in this context, speci cally in the branch involving Quantum Communication. The thesis is structured as follows.
A brief introductory chapter offers a quick sight over the issue of Quantum Information/Computation and introduces the motivations bringing to the necessity of faithful quantum state transfer.
In the successive chapter we focus over a particular set of quantum systems employable as quantum communication lines, i.e. spin networks. Initially we pay attention principally to the simplest instantiations, monodimensional spin chains: we expose some of the main models to describe spin chain dynamics and then present some transmission protocols with concise
discussion about their performances. Here we show how sender/receiver actions and control over the system can affect positively or negatively the state transfer. Specifcally we nd that a high-frequency measurement regime spoils the transmission and that the opportune tuning in spin interaction can enhance it (in terms of delity). A short discussion about Quantum Zeno Effect is added in relation to the \high-frequency measurement regime" and some considerations are made about transfer speed in such systems.
In the third and last chapter, recalling the considerations mentioned above, we try to address the issue of information propagation speed in quantum spin networks. To do so we take advantage of those tools offered by 1972 Lieb and Robinson's work known as Lieb-Robinson bound.
They found that in spin systems excitations enabled by local operators can travel within a nite speed that de nes a sort of light-cone, outside of which correlation are exponentially depressed. In the landscape of Quantum Communication we try to apply this kind of results to understand for instance how noise worsen the communication, how the bound affects
state discriminability. We discuss how certain bounds in the literature can be improved.
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