The Power of No-Signalling Attacks and Implications for (Quantum) Non-Locality Distillation

You are cordially invited to attend the PhD Dissertation Defense of Benno SALWEY on Tuesday, May 26th 2015 at 14h30 in room SI-003 (Informatics building)

Abstract:
The phenomenon of non-locality, which arises when entangled quantum systems are suitably measured, is perhaps one of the most puzzling features of quantum theory to the philosophical mind. It implies that these measurement statistics cannot be explained by hidden variables, as promoted by Einstein, and suggests that our universe may not be, in principle, a well determined entity where the uncertainty we perceive in physical observations stems only from our lack of knowledge of the whole.

Besides its philosophical impact, non-locality is also a resource for information theoretic tasks since it implies secrecy; if non-locality limits the predictive power that any hidden variable (in the universe) can have about some observations, then it limits in particular the predictive power of a hidden variable hold by an adversary in a cryptographic scenario. We will investigate whether non-locality alone can empower two parties to perform unconditionally secure communication in a feasible manner when only necessary assumptions are made for such a task to be possible -- independent of the validity of any physical theory (such as quantum theory).

Non-locality is also of interest when studying the foundations of quantum theory and the principles which stand beyond its mathematical formalism. In an attempt to single out quantum theory within a broader set of theories the study of non-locality may help to point out intuitive principles which distinguish it from the rest. In theories where the limits by which quantum theory constraints the strength of non-locality are surpassed, many 'principles' on which an information theorist would rely are shattered -- one example is the hierarchy of communication complexity as the latter becomes completely trivial once a certain degree of non-locality is overstepped.

To study the structure of such 'super-quantum theories' we will also investigate the phenomenon of distillation of non-locality, the ability to distill stronger forms of non-locality from weaker ones. By exploiting again the inherent connection between non-locality and secrecy we provide a novel way to derive bounds on non-locality distillation protocols through an adversarial view on the problem.

Dissertation Committee:

• Prof. Stefan Wolf, Università della Svizzera italiana, Switzerland (Research Advisor)
• Prof. Gilles Brassard, Université de Montréal, Canada (Research co-Advisor)
• Prof. Marc Langheinrich, Università della Svizzera italiana, Switzerland (Internal Member)
• Prof. Igor Pivkin, Università della Svizzera italiana, Switzerland (Internal Member)
• Prof. Nicolas Brunner, Université de Genève, Switzerland (External Member)
• Prof. Omar Fawzi, École Normale Supérieure de Lyon, France (External Member)