Research Fellows Directory
Professor Sandu Popescu
University of Bristol
During the financial year April 2016-April 2017 my main research focus was on various fundamental quantum effects.
First of all, with Y. Aharonov and D. Rohrlich, we continued our work on conservation laws in quantum mechanics. Conservation laws, such as those for energy, momentum and angular momentum, are among the most fundamental laws of nature. As such, they have been intensively studied and extensively applied. First discovered in classical mechanics, they are at the core of all subsequent physical theories, non-relativistic and relativistic, classical and quantum. But our results raise fundamental questions about the meaning of conservation laws in quantum mechanics and we argued that the standard way of defining conservation laws, while perfectly valid as far as it goes, misses essential features of nature and has to be revised and extended.
In a different direction, we studied processes with indefinite causal order. When describing physical phenomena it is commonly assumed that there exists an underlying causal order. Loosely speaking, later events can be influenced by previous ones, but not the other way around. Recently however, the idea that physical theories necessarily require a causal order has been challenged, in particular in the context of quantum theory. Indeed, one may imagine that the notion of causal order can be subject to fundamental quantum principles, such as the superposition or uncertainty principle, resulting in indefinite causal structures. We gave a new perspective on this issue by showing that quantum theory with fundamental post-selection can lead to such structures and showed that this quantum theory is equivalent to the formalism of “process matrices” recently proposed by other researchers.
Interests and expertise (Subject groups)