What is so strange about quantum mechanics? Before the advent of quantum information there were many good answers to this question. With the development of fields such as quantum encryption and quantum computing, however, more sophisticated answers are needed. There is now thriving research into the foundational structure of quantum theory.
This work tackles questions such as: How does quantum reality differ from classical reality? What is quantum entanglement? Do quantum systems possess properties? How does relativity affect quantum physics? Remarkably such questions can be cast into precise mathematical terms, and we can arrive at concrete answers through the language of quantum information. Beyond the conceptual value, these results also find applications in a range of wholly practical tasks in quantum information science.
We are developing a framework for quantum theory that takes the four-dimensional, spacetime nature of the physical world of relativity to heart. The framework is based on the path integral or sum-over-histories and we are working towards making it mathematically well-defined and also discovering what corresponds the physical world within the path integral approach. Our current work is focussed on the proposal that the physical world in quantum theory is an answer to every yes-no question that can be asked about it.
The physical laws of the world of our daily experiences ("classical physics") are very different from those of quantum mechanics governing the behaviour of microscopic particles such as electrons and atoms. Given that the world is ultimately made up of these small "quantum" building blocks, this discrepancy in behaviour is a little puzzling. A focus of the work of my group is quantum-classical correspondence: trying to understand the connections between quantum and classical physics better. We also work on certain open quantum systems, where particles can leave or enter the system of interest. We describe these using different models, such as complex energies and non-Hermitian Hamiltonians, as well as Lindblad equations.