2019 James Clerk Maxwell Medal and Prize
Dr Adam Nahum for his outstanding contributions to understanding universal aspects of many-body quantum systems both in and out of equilibrium.
Adam Nahum's work is characterised by emphasis on the ‘universal’ physics which unites large families of complex physical systems, and by an ability to capture this physics using elegant minimal models.
Nahum's work on non-equilibrium dynamics introduced new theoretical paradigms for understanding strongly coupled quantum systems far from their ground state. In particular he has shed light on the quantum ‘butterfly effect’: the growth of correlations and quantum entanglement between distant parts of a quantum system. This has involved forging unexpected connections between strongly-coupled quantum dynamics and archetypal problems in classical statistical mechanics. Nahum and his collaborators used exact mappings, in strikingly simple minimal models, to give new universal predictions for correlation functions and entanglement dynamics in complex quantum systems such as spin chains. These approaches are being extended in a wide range of directions by several groups, and various predictions have already been verified using computer simulations.
In a separate strand of his research, Nahum has made important and surprising contributions to unconventional critical behaviour in quantum magnets. He used novel mappings to unveil new types of quantum criticality, and also new phenomena at theoretically important ‘deconfined’ quantum phase transitions in planar magnets. These phenomena include a very accurate emergent symmetry which arises without fine-tuning at deconfined phase transitions: first identified numerically, and subsequently understood in terms of new field-theoretic dualities, in work with two sets of collaborators. These results have far-reaching implications for quantum field theory in three spacetime dimensions, as well as for frustrated magnets at low temperature.
Nahum's work often involves visualizing physical systems in geometrical terms, through relations to statistical ensembles of random walks or fluctuating membranes. He has also obtained key results for such ensembles in their own right, discovering new universality classes for interacting random walks and finding new relations between polymers or ‘loop soups’ and field theory.
By injecting new concepts at the interface between classical and quantum statistical mechanics, Nahum has opened up many exciting directions in emergent quantum phenomena. The originality of his approaches and the wide variety of different physical phenomena he addresses are exceptional.