Research
Topological Matter and Quantum Criticality
We investigate low-temperature quantum systems exhibiting topological phases of matter. Hallmark emergent features are indestructible edge currents, or quasi-particles with generalized exchange statistics. We recently uncovered new physically-motivated mechanisms for stabilizing such states, and there are indications that this can be generalized. An equally important line of research is pin-pointing ways of detecting these states.
Tuning between such distinct low-temperature phases of matter can moreover lead to quantum critical points with emergent conformal symmetry. We showed that topological features can persist in such extreme conditions. In fact, certain topological states can appear only in critical systems. This signals a much wider landscape to explore! What is the general interplay between topology and criticality?
Emergent Phenomena in Quantum Devices
For decades, there have been fascinating theoretical discoveries of what can emerge if one is able to choreograph the interactions or entanglement of particles. It is now gradually becoming possible to realize and control such phenomena due to the development of quantum devices which are much more tuneable than conventional materials. Our group makes use of this opportunity to explore emergent phenomena, which in turn inspires new theoretical insights.
For instance, we proposed how the strong Rydberg interactions of atoms trapped in optical tweezers can be used to realize a topological phase of matter (‘Z2 spin liquid’ or ‘toric code order’). In collaboration with the Lukin lab, this was implemented shortly thereafter, where we probed the emergent gauge theory using string correlations. We also proposed how to prepare exotic states such as non-Abelian topological order and gauge theories. This was implemented in Quantinuum’s cold ion processor, showcasing the first unambiguous sighting of non-Abelian anyons. Both experiments are accessibly described in Quanta Magazine articles here and here. In addition to further exploring the landscape of phenomena, we will investigate how to use such states for sensing, computation, or fundamental science.
Many-Body Quantum Information
Quantum Information Theory (QIT) characterizes quantum systems not in terms of energetics or interactions, but rather as resources—how difficult are they to create, and what can one do with them? E.g., an entangled Bell pair is a resource for teleporting quantum information. QIT concepts even underlie the modern definition of phases of matter: states are said to be in the same phase if and only if they can be transformed into one another with a quantum circuit whose depth is independent of system size.
In our group, we study the interplay between QIT and many-body physics: how can concepts from one be used to achieve something new in the other? For instance, we showed how the classification of phases of matter changes once one allows measurements as an additional ingredient. In particular, we found a version of many-body teleportation which essentially teleports between phases of matter. We subsequently used this to create non-Abelian topological order by measuring ions. We also go the other direction, e.g., showing how concepts from the quantum many-body community give a new route to measurement-based quantum computation.
Unification and Universality
In physics, the goal of unifying laws and concepts applies not only the most fundamental or microscopic theories. In our group, we search for connections between the emergent laws describing many-body quantum systems. One motivating factor is that such unifications provide a deeper understanding; in addition, they can lead to new ideas for experimental realizations or applications.
One example is a newfound understanding of superconductors. Although they are sometimes vaguely described as ‘spontaneous gauge symmetry breaking‘, we argued that they are best understood as a phase of matter known from seemingly-unrelated areas of many-body quantum physics. This unifies the theories of superconductivity and symmetry-protected topological phases. We have also unified various distinct approaches to topological order. Moreover, as an example of universality, we showed that quantum Ising models can capture all other known qudit Hamiltonians!
Tensor Networks
under construction
Quantum Dynamics
under construction
