Fundamental Aspects of Quantum Mechanics and their Interplay with Quantum Information

Abstract

Quantum Mechanics has been a spectacularly successful theory. It correctly predicts and explains the phenomena of subatomic particles, nuclei, atoms, molecules et cetera. Whether quantum mechanics applies to observers has been a long thought problem. Wigner’s Friend is a thought experiment that illustrates this. Of late, there has been a surge of interest in the Wigner’s Friend thought experiment. Extended Wigner Friend Scenarios (EWFS) involving ‘entangled friends’ have been proposed to test whether quantum theory is applicable to observers. In this work, we systematically analyze the recently proposed ‘Local Friendliness’ inequalities in the context of bipartite EWFS with respect to pure states and the Werner states. Further, we formulate various Extended Wigner Friend Scenarios, and identify the trivial scenarios. For each of these EWFS, we attempt to specify the structure of the Local Friendliness polytope, thereby characterizing the correlations allowed by the Local Friendliness assumptions. In the scenarios where ‘Genuine Local Friendliness’ inequalities have been found, we provide their quantum mechanical bounds.