


2019-01-18
ION HANCU
ION HANCU

2019-01-29
MARIA MAFFEI
MARIA MAFFEI

2019-02-13
BORIS BOURDONCLE
BORIS BOURDONCLE

2019-02-15
JORDI MORALES DALMAU
JORDI MORALES DALMAU

2019-02-22
FRANCESCO RICCI
FRANCESCO RICCI

2019-03-06
CLARA GREGORI
CLARA GREGORI

2019-03-26
ALEXIA SALAVRAKOS
ALEXIA SALAVRAKOS

2019-04-12
SENAIDA HERNANDEZ SANTANA
SENAIDA HERNANDEZ SANTANA

2019-04-15
DAVID RAVENTÓS RIBERA
DAVID RAVENTÓS RIBERA

2019-04-16
PETER SCHMIDT
PETER SCHMIDT

2019-04-29
CALLUM O’DONNELL
CALLUM O’DONNELL

2019-05-02
LUCIANA VIDAS
LUCIANA VIDAS

2019-05-03
HANYU YE
HANYU YE

2019-05-10
TANJA DRAGOJEVIC
TANJA DRAGOJEVIC

2019-05-17
FLAVIO BACCARI
FLAVIO BACCARI

2019-06-04
MARTINA GIOVANNELLA
MARTINA GIOVANNELLA

2019-07-02
OZLEM YAVAS
OZLEM YAVAS

2019-07-03
ALESSANDRO SERI
ALESSANDRO SERI

2019-07-11
RENWEN YU
RENWEN YU

2019-09-06
ALEXANDER BLOCK
ALEXANDER BLOCK

2019-10-04
MARCO PAGLIAZZI
MARCO PAGLIAZZI

2019-10-07
RINU MANIYARA
RINU MANIYARA

2019-10-15
ALEJANDRO POZAS-KERSTJENS
ALEJANDRO POZAS-KERSTJENS
Certification of Many-Body Systems


Flavio Baccari
May 17th, 2019
FLAVIO BACCARI
Quantum Information Theory
ICFO-The Institute of Photonic Sciences
Quantum physics is arguably both the most successful and the most counterintuitive physical theory of all times. Its extremely accurate predictions on the behaviour of microscopic particles have led to unprecedented technological advances in various fields and yet, many quantum phenomena defy our classical intuition.
Starting from the 1980’s, however, a paradigm shift has gradually taken hold in the scientific community, consisting in studying quantum phenomena not as inexplicable conundrums but as useful resources. This shift marked the birth of the field of quantum information science, which has since then explored the advantages that quantum theory can bring to the way we process and transfer information.
In this thesis, we introduce scalable certification tools that apply to various operational properties of many-body quantum systems. In the first three cases we consider, we base our certification protocols on the detection of nonlocal correlations. These kinds of non-classical correlations that can displayed by quantum states allow one to assess relevant properties in a device-independent manner, that is, without assuming anything about the specific functioning of the device producing the state of interest or the implemented measurements.
In the first scenario we present an efficient method to detect multipartite entanglement in a device-independent way. We do so by introducing a numerical test for nonlocal correlations that involves computational and experimental resources that scale polynomially with the system number of particles. We show the range of applicability of the method by using it to detect entanglement in various families of multipartite systems. In multipartite systems, however, it is often more informative to provide quantitative statements. We address this problem in the second scenario by introducing scalable methods to quantify the nonlocality depth of a multipartite systems, that is, the number of particles sharing nonlocal correlations among each other. We show how to do that by making use of the knowledge of two-body correlations only and we apply the resulting techniques to experimental data from a system of a few hundreds of atoms. In the third scenario, we move to consider self-testing, which is the most informative certification method based on nonlocality. Indeed, in a self-testing task, one is interested in characterising the state of the system and the measurement performed on it, by simply looking at the resulting correlations. We introduce the first scalable self-testing method based on Bell inequalities and apply it to graph states, a well-known family of multipartite quantum states. Moreover, we show that the certification achieved with our method is robust against experimental imperfections. Lastly, we address the problem of certifying the result of quantum optimizers. They are quantum devices designed to estimate the groundstate energy of classical spin systems. We provide a way to efficiently compute a convergent series of upper and lower bounds to the minimum of interest, which at each step allows one to certify the output of any quantum optimizer.
Friday, May 17, 10:30. ICFO Auditorium
Thesis Advisor: Prof Dr Antonio Acín
ICFO-The Institute of Photonic Sciences
Quantum physics is arguably both the most successful and the most counterintuitive physical theory of all times. Its extremely accurate predictions on the behaviour of microscopic particles have led to unprecedented technological advances in various fields and yet, many quantum phenomena defy our classical intuition.
Starting from the 1980’s, however, a paradigm shift has gradually taken hold in the scientific community, consisting in studying quantum phenomena not as inexplicable conundrums but as useful resources. This shift marked the birth of the field of quantum information science, which has since then explored the advantages that quantum theory can bring to the way we process and transfer information.
In this thesis, we introduce scalable certification tools that apply to various operational properties of many-body quantum systems. In the first three cases we consider, we base our certification protocols on the detection of nonlocal correlations. These kinds of non-classical correlations that can displayed by quantum states allow one to assess relevant properties in a device-independent manner, that is, without assuming anything about the specific functioning of the device producing the state of interest or the implemented measurements.
In the first scenario we present an efficient method to detect multipartite entanglement in a device-independent way. We do so by introducing a numerical test for nonlocal correlations that involves computational and experimental resources that scale polynomially with the system number of particles. We show the range of applicability of the method by using it to detect entanglement in various families of multipartite systems. In multipartite systems, however, it is often more informative to provide quantitative statements. We address this problem in the second scenario by introducing scalable methods to quantify the nonlocality depth of a multipartite systems, that is, the number of particles sharing nonlocal correlations among each other. We show how to do that by making use of the knowledge of two-body correlations only and we apply the resulting techniques to experimental data from a system of a few hundreds of atoms. In the third scenario, we move to consider self-testing, which is the most informative certification method based on nonlocality. Indeed, in a self-testing task, one is interested in characterising the state of the system and the measurement performed on it, by simply looking at the resulting correlations. We introduce the first scalable self-testing method based on Bell inequalities and apply it to graph states, a well-known family of multipartite quantum states. Moreover, we show that the certification achieved with our method is robust against experimental imperfections. Lastly, we address the problem of certifying the result of quantum optimizers. They are quantum devices designed to estimate the groundstate energy of classical spin systems. We provide a way to efficiently compute a convergent series of upper and lower bounds to the minimum of interest, which at each step allows one to certify the output of any quantum optimizer.
Friday, May 17, 10:30. ICFO Auditorium
Thesis Advisor: Prof Dr Antonio Acín