Tomorrow Ladina Hausmann will tell us about her semester project with Nuriya and Lídia, "On multi-agent logical paradoxes in epistemically-restricted hidden variable theories". See below for the abstract. The zoom link is https://ethz.zoom.us/j/362994444.

Best,

-joe

Abstract: The Frauchiger-Renner paradox shows that inconsistencies appear when multiple agents reason about each other in quantum mechanics [1]. But is this a distinct feature of quantum theory, or can other physical theories exhibit similar paradoxes? We know that it is possible to find a paradoxical setting in box world, a theory less local than 

quantum mechanics, for a specific model of physical agents [2].

In this project we investigate multi-agent logical paradoxes in Spekkens' toy theory. Spekkens' toy theory exhibits many phenomena of quantum mechanics, but is a non-contextual local hidden variable theory [3]. The quantum-like effects stem from an epistemic restriction akin to the uncertainty principle, and a measurement disturbance rule.

We were able to prove that there is no Frauchiger-Renner-like paradox in Spekkens' toy theory. In addition, we refined the formalism of Spekkens'  toy theory and were able to model agents' physical memories and deterministic reasoning.

In this talk, I will give an introduction to Spekkens' toy theory. Additionally, I will present how memory update and reasoning work in the toy theory. In the end, I'll discuss the Frauchiger-Renner paradox in Spekkens' toy theory.

[1]  Daniela Frauchiger and Renato Renner.  Quantum theory cannot 

consistently describe the use of itself. Nature  Communications, 9(1),  

sep 2018.  doi:10.1038/s41467-018-05739-8.

[2]  V  Vilasini,  Nuriya  Nurgalieva,  and  Lídia  del  Rio. 

Multi-agent  paradoxes beyond quantum theory. New J. Phys., 

21(11):113028, nov 2019. doi:10.1088/1367-2630/ab4fc4.

[3]  Robert  W.  Spekkens. Evidence  for  the  epistemic  view of  

quantum  states:    A  toy  theory. Physical  Review  A, 75(3),  mar  

2007. doi:10.1103/physreva.75.032110.