Gunnar is a condensed matter theorist with an interest in strongly correlated materials. He currently holds a Royal Society University Research Fellowship in the department, which allows him to develop ambitious new approaches for numerical simulations of materials such as superconductors or heavy fermion compounds. Gunnar has graduated with a French master's degree (Diplome d'Etudes Approfondies) in Theoretical Physics from the Ecole Normale Supérieure in Paris (2003). He pursued his PhD at the University of Paris XI as a member of the Laboratoire de Physique Théorique et Modèles Statistiques. During his doctoral studies, he also visited Prof. Steve Simon's group at the Bell Laboratories, Murray Hill, NJ. On completion of his PhD in 2006, Gunnar moved to Cambridge, UK, to take up a postdoctoral position in the group of Prof. Nigel Cooper. He has developed his personal line of research on strongly correlated phases of matter as a Research Fellow at the Cavendish Laboratory thanks to the support of several prestigious fellowship awards, including a Trinity Hall Research Fellowship (2008-2011), a Leverhulme Early Career Fellowship (2011-2013), and a Royal Society University Research Fellowship (2013-2016). His international collaborations were supported by an ICAM Fellowship for a collaboration with Prof. Victor Gurarie at UCO Boulder (2008-10), and by a CNRS visiting researcher position for collaboration with Dr Jerome Dubail, Université de Lorraine, Nancy, France (2015-16). Gunnar has joined the faculty at the University of Kent in May 2016.
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My research revolves around the interplay of strong interactions and topology, which can give rise to collective phases of matter with exciting new properties. Some of the most interesting topological phenomena can be found in two-dimensional quantum systems. A prominent example are fractional quantum Hall phases of electrons in strong magnetic fields, which realise fractionalized quasiparticles that carry fractions of the charge of an electron. More excitingly, they can also carry so-called non-Abelian exchange statistics which allow one to manipulate the many-body quantum state in a well-defined manner through the controlled movement of quasiparticles, providing an ideal platform for quantum computation. In practice, my work covers two main aspects of investigation:
Developing high performance numerical simulations of strongly correlated materials
I develop new computer simulations of various different flavours. My approach relies on combining analytical insights into collective properties of emergent phases at low temperatures on one hand, with quantitative modelling techniques for microscopic correlations on the other hand. This combination provides powerful tools which can give insights into a wide range of strongly correlated materials, spanning topics such as correlated superconductors and frustrated magnetism.
- Exact diagonalisation: I am a main developer of the DiagHam library for simulations of spin systems and fractional quantum Hall physics.
- Variational Quantum Monte Carlo: My group has explored the physics of fractional quantum Hall states using a range of variational QMC techniques, such as energy and variance minimisation.
- Diagrammatic Monte Carlo: Perturbative expansions in quantum field theories can be represented graphically by Feynman diagrams. We use stochastic sampling techniques in the space of Feynman graphs to analyse the properties of novel quantum phases, exploring the physics of unitary Fermi gases and the Hubbard model.
- Matrix / Tensor Product States: Insights from quantum information theory have given rise to new tools for simulating strongly interacting matter. In particular, topological phases are well suited for descriptions in terms of their local entanglement. We exploit this property to develop numerical approaches capturing the physics of fractional topological insulators.
Realising novel phases of matter
Part of my research focuses on realising exciting new phases by "quantum engineering", using the tools of materials science, or cold atomic gases. Examples include the creation of systems with synthetic magnetic fields, which arise from strain or spin-orbit coupling in solid state materials, and can also be generated using light-matter coupling for cold atomic gases. As a theorist, I am most interested in using such models to explore new types of topological phases such as fractional Chern insulators, topological superfluids, as well as new types of symmetry breaking phases such as supersolid phases.back to top