# Siddharth Parameswaran

# Siddharth Parameswaran

Associate Professor

I am a theoretical physicist working on quantum many-body systems. I am broadly interested in all aspects of condensed matter, and particularly in unusual phenomena that emerge as a result of strong interactions or in non-equilibrium settings. In recent years, I have worked extensively on topological phases of matter, non-equilibrium dynamics, and many-body localized systems. I also actively collaborate with experimental groups, both at Oxford and around the world.

Systems of interacting particles can display a variety of emergent cooperative phenomena that cannot be understood from their microscopic details. Usually, the study of this type of "condensed matter" builds on two key principles, namely (i) that most situations can be understood by approximately treating the constituents (such as electrons, atoms, or molecules) as weakly interacting; and (ii) that the assumption of thermal equilibrium provides a powerful way to capture the properties of complex systems using simple statistical tools.

I'm interested in what happens when quantum systems are so strongly interacting, or so dramatically disturbed from equilibrium, that these guiding principles break down. A new set of analytical and computational ideas is therefore required to fully understand the behaviour of such systems, and to explore their properties. Besides their great fundamental interest, many of the new phenomena displayed in these extreme regimes could have many important applications. Insights into weakly-correlated, equilibrium systems fueled the technological revolution of the second half of the twentieth century; what new and unexpected benefits might we accrue from understanding their more complex cousins?

On a technical level, my research is centred around two primary themes. The first is the interplay of crystal symmetries with strong correlations and topological effects, and the new states of matter that can emerge as a consequence, in settings such as correlated insulators, topological semimetals, and two-dimensional quantum Hall systems. The second is the dynamics of far-from-equilibrium systems, with a particular focus on many-body localized phases, the many-body localization phase transition, and unconventional transport mechanisms. Both have substantial and increasing benefit from making contact with ideas from quantum information, particularly as it relates to entanglement and measurement. I have a strong interest in working with experimental groups; recent collaborations include those with the groups of Ali Yazdani (Princeton), Amalia Coldea (Oxford), David Weld (UCSB), and Radu Coldea (Oxford).

My research is supported by the Horizon 2020 Program of the European Research Council via a Starting Grant focused on Topological Matter and Crystalline Symmetries [Grant No. 804213-TMCS] and by a UK Engineering and Physical Sciences Research Council grant to the Oxford Condensed Matter Theory group on Coherent Many-Body Quantum States of Matter [EP/S020527/1].

I am currently lecturing the C6 theory option for MPhys students; these also constitute the Advanced Quantum Theory course in the Oxford MMathPhys course.

I am a Tutorial Fellow of Hertford College. While the topics I tutor vary from year to year, papers I have covered include 2nd year statistical/thermal physics (A1) and Mathematical Methods and Quantum Mechanics (A3), and 3rd year Atomic Physics (B3), General relativity (B5), and Condensed Matter (B6).