Aspects of nonlocality and quantum thermodynamics

This thesis is a tale of two stories. The first half of this thesis is dedicated to the study of nonlocality. We know that nature is inherently nonlocal, however, the nonlocal correlations allowed by quantum mechanics are limited; we could conceivably have correlations which are 'more' nonlocal and still cause no conflict with relativity. In this thesis I explore this limita- tion by studying nonlocality beyond quantum mechanics from a number of directions, relating mostly to dynamics and transformations. I show that the analogue of entanglement swapping and teleportation can in fact be implemented in a maximally nonlocal theory, as well as in theories with arbitrary limits on their nonlocality, Furthermore I show that nonlocality can be distilled, similarly to entanglement. This leads on to the study of when a nonlocal theory is dosed under a natural set of operations. Finally I make a tentative attempt at studying measures of nonlocality, by introducing notions of nonlocal cost and distillable nonlocality. The second half of this thesis is dedicated to the study of quantum thermodynamics. I explore the question of what are the absolute limits on the size of thermal machines? I present simple models of both quantum refrigerators as well as work-producing quantum heat engines, the smallest consisting of only a single qutrit coupled to two thermal baths. I show that both machines can reach the Carnot efficiency, and also that the refrigerator is able to cool towards absolute zero.EThOS - Electronic Theses Online ServiceGBUnited Kingdo