Tesi etd-10022022-231628 |
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Tipo di tesi
Tesi di laurea magistrale
Autore
CATALANO, GIUSEPPE
URN
etd-10022022-231628
Titolo
Efficiency Analysis of Continuous Variable Quantum Communication Lines in the Presence of Fluctuating Parameters
Dipartimento
FISICA
Corso di studi
FISICA
Relatori
relatore Prof. Giovannetti, Vittorio
relatore Prof. De Palma, Giacomo
correlatore Dott. Fanizza, Marco
relatore Prof. De Palma, Giacomo
correlatore Dott. Fanizza, Marco
Parole chiave
- quantum information
- quantum communication
- continuous-variable
- gaussian channel
- lossy channel
- convex combination
- fluctuating parameters
Data inizio appello
24/10/2022
Consultabilità
Non consultabile
Data di rilascio
24/10/2092
Riassunto
In the context of Quantum Communication theory, a lossy channel is a quantum channel that can describe a wide variety of scenarios that cause an attenuation of the input signal, such as the transmission in an optical fiber or free-space communication. From the mathematical point of view, a lossy channel is described as an interaction, mediated by a beam-splitter with fixed transmissivity, between the input state and the environment state, which is the vacuum state.
In some realistic situations, such as the transmission of photons through the atmosphere, the noise that affects the quantum carrier cannot be described by a single lossy channel, because of the fluctuations in the loss parameter. Therefore, it is better to model these scenarios considering an ensemble of lossy channels.
The classical capacity of a quantum channel is the asymptotic rate of transmission of classical information, sent from a sender to a receiver, when the quantum system that carries the information is subject to the noise described by the quantum channel. If the sender and receiver share an unlimited amount of entanglement that can be used to improve communication, one can define the entanglement-assisted classical capacity.
In this work, we studied some families of channels, that are convex combinations of two different lossy channels and, in order to describe such convex combinations, we used an ancillary qubit that selects one or the other channel. We found that, for those channels, there exist quantum states with a better communication performance with respect to the thermal state with the same energy; this is surprising because it is known that a thermal state is the best choice for a single lossy channel. However, using the methods developed in this Thesis, it is possible to model even more general scenarios, in order to improve the quantum communication performance in the presence of more realistic noises.
In some realistic situations, such as the transmission of photons through the atmosphere, the noise that affects the quantum carrier cannot be described by a single lossy channel, because of the fluctuations in the loss parameter. Therefore, it is better to model these scenarios considering an ensemble of lossy channels.
The classical capacity of a quantum channel is the asymptotic rate of transmission of classical information, sent from a sender to a receiver, when the quantum system that carries the information is subject to the noise described by the quantum channel. If the sender and receiver share an unlimited amount of entanglement that can be used to improve communication, one can define the entanglement-assisted classical capacity.
In this work, we studied some families of channels, that are convex combinations of two different lossy channels and, in order to describe such convex combinations, we used an ancillary qubit that selects one or the other channel. We found that, for those channels, there exist quantum states with a better communication performance with respect to the thermal state with the same energy; this is surprising because it is known that a thermal state is the best choice for a single lossy channel. However, using the methods developed in this Thesis, it is possible to model even more general scenarios, in order to improve the quantum communication performance in the presence of more realistic noises.
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