## Thesis etd-09032021-145319 |

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Thesis type

Tesi di laurea magistrale

Author

BACCIOTTINI, LEONARDO

URN

etd-09032021-145319

Thesis title

Encoding and extracting a classical Internet packet from a qubit: issues, algorithms and their performance evaluation

Department

INGEGNERIA DELL'INFORMAZIONE

Course of study

COMPUTER ENGINEERING

Supervisors

**relatore**Prof. Mingozzi, Enzo

**relatore**Prof. Anastasi, Giuseppe

**relatore**Prof. Lenzini, Luciano

Keywords

- Chernoff bound
- closed timelike curve
- deutschian CTCs
- quantum algorithm
- quantum Internet
- retrieval of an n-bit string from a single qubit
- simulation
- violation of Holevo bound

Graduation session start date

24/09/2021

Availability

Full

Summary

The Quantum Internet has been conceived as a disruptive communication paradigm to transfer qubit states among different computers so as to support applications which are out of reach for the current Internet. Using qubits to convey classical internet packets (basically n-bit strings of classical information) through the Quantum Internet is a challenging issue which is thoroughly investigated in the thesis. An infinite amount of information can be encoded in the amplitudes of a qubit. However this information cannot be accessed easily: when a qubit is measured it collapses either on 0 or 1, losing everything that was stored inside.

Holevo’s theorem sets an upper bound, stating that only one classical bit of information can be reliably extracted from a qubit and this looks pretty bad for our purposes. The transmission of two bits via a single qubit is made possible by the Superdense coding protocol. However the bit length of a packet is much higher than 2!

The violation of the Holevo bound, and thus the retrieval of an n-bit string from a single qubit, is made possible by the Deutschian closed timelike curve (D-CTC). In this thesis we focus on an iterative algorithm to simulate the presence of a D-CTC and extract n-bits of information from a qubit state. We evaluate the performances of this algorithm and compare its outcomes with a theoretical limit, called the Quantum Chernoff bound. The insights gained during the performance analysis allowed us to formulate a number of coding proposals which outperform those of the assessed algorithm.

Holevo’s theorem sets an upper bound, stating that only one classical bit of information can be reliably extracted from a qubit and this looks pretty bad for our purposes. The transmission of two bits via a single qubit is made possible by the Superdense coding protocol. However the bit length of a packet is much higher than 2!

The violation of the Holevo bound, and thus the retrieval of an n-bit string from a single qubit, is made possible by the Deutschian closed timelike curve (D-CTC). In this thesis we focus on an iterative algorithm to simulate the presence of a D-CTC and extract n-bits of information from a qubit state. We evaluate the performances of this algorithm and compare its outcomes with a theoretical limit, called the Quantum Chernoff bound. The insights gained during the performance analysis allowed us to formulate a number of coding proposals which outperform those of the assessed algorithm.

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