Darwinismo quântico e contextualidade

Author(s)

Roberto Dobal Baldijão

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2022-02-03

Examining board members

Marcelo de Oliveira Terra Cunha; John Harry Selby; Matthew Fairbairn Pusey; Rafael Luiz da Silva Rabelo; Gustavo Silva Wiederhecker

• Advisor: Marcelo de Oliveira Terra Cunha

Abstract

In this thesis we tackle the following problem: on the one hand, quantum contextuality reveals a crucial form of nonclassicality in quantum theory; on the other hand, our everyday experience is well-described by classical, non- contextual, descriptions. How can quantum theory explain our noncontextual everyday experience? Is there some classical limit able to make quantum con- textuality disappear? In pursue of an answer to such questions, we first analyze a scenario in which a sequence of observers tries to violate some odd N-cycle noncontex- tuality inequalities, using the best known quantum realization. Under this setting, witnessing contextuality rapidly becomes impossible. This sequential setup can be related to that of an environment made of several subsystems, which interacts with the central system in a collisional-model-like manner. In this interpretation, noncontextuality emerges in a very special environment. Such an analysis suggests an investigation focused on quantum Darwinism as a classical limit capable of making noncontextuality emerge. Quantum Dar- winism, indeed, is arguably responsible for the emergence of objectivity, as we experience in our (apparently classical) world. The sequential scenario described above is arguably special, therefore it cannot be considered as a good approximation of typical Darwinist settings. Seeking for a more general description, we use the approach of Brandão, Pi- ani & Horodecki to quantum Darwinism and, taking Spekkens notion of contextuality, we are able to prove that sufficiently successful Darwinism processes indeed lead to the emergence of noncontextuality – and we show this without having to discuss particular aspects of the system-environment interaction [5]. We thus reach our first goal. There is, nonetheless, a patent asymmetry among the main ingredients of this thesis, quantum Darwinism and contextuality: the latter is better under- stood without having to talk about quantum theory, while the former is in- herently linked to the quantum formalism. The second main problem we deal with in this thesis arises: can we put Darwinism into more general terms? ii What can we learn from this? With this new goal, we describe one idealized form of Darwinism – driven by CNOT-like fan-out interactions– to the framework of generalized proba- bilistic theories (GPTs). Within a language that does not lean on the quantum formalism, we can go beyond contemplating that quantum Darwinism pro- cesses exist, being able to discuss which principles are necessary or sufficient to enable such processes in the first place. Additionally, we describe Darwin- ism in one particular non-quantum theory, namely, Spekkens’ toy model. This model has had crucial impacts on the foundations of physics, and carry- ing a Darwinist process shows that such a path to the emergence of a classical world is not particular to quantum theory. Moreover, it shows that the suffi- cient conditions we find for Darwinism are not tight. Finally, this endeavour of generalizing Darwinism to GPTs, in the context of this thesis, also points to a clear perspective, which will hopefully be studied in the future: to analyze the emergence of noncontextuality within GPTs (AU)

• FAPESP's process: 16/24162-8 - Quantum Darwinism and contextuality
• Grantee: Roberto Dobal Baldijão
• Support Opportunities: Scholarships in Brazil - Doctorate