Research
what we work on — click a topic on the map to read more
Our group explores the intersection of quantum many-body physics and quantum information science. A recurring theme is that the concepts of quantum information (entanglement, coherent information, error correction) are the right language for describing many-body quantum matter, and in turn that many-body physics provides the tools for understanding what can be done with large, noisy, or dynamically evolving quantum systems. The publications page has the full list of papers (see also Google Scholar).
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Many-body physics of quantum information
What happens to a many-body quantum state when it decoheres? We study mixed-state phases of matter and the transitions between them, using information-theoretic quantities such as the coherent information as order parameters. This includes the exact characterization of error thresholds in stabilizer codes as phase transitions, topological mixed states, symmetry-protected topological phases under decoherence, and new forms of symmetry breaking (strong-to-weak spontaneous symmetry breaking) that exist only in mixed states. Related work uses the entanglement bootstrap to derive the properties of topological order from the structure of entanglement alone.
Representative papers: exact coherent information for toric codes under decoherence, quantum criticality under decoherence or weak measurement, topological mixed states.
Quantum error correction
We design and analyze quantum error-correcting codes, with a focus on high-rate quantum low-density parity-check (LDPC) codes that dramatically reduce the qubit overhead of fault tolerance. Directions include design principles for ultra-high-rate codes, lifted-product code constructions with addressable logical operators, and approximate quantum error correction at the edges of chiral topological phases.
Representative papers: design principles for ultra-high-rate quantum codes, logical spectroscopy, lifting lifted product codes.
Non-equilibrium dynamics and quantum control
Measurements, dissipation, and driving can stabilize phases that have no equilibrium counterpart. We study measurement-prepared quantum phases and their transitions, Floquet-enriched topological order, the low-energy structure of Lindbladian dynamics and its relation to emergent hydrodynamics, and spectral gaps of dissipative random circuits. On the control side, we work with experimental collaborators on programmable quantum simulators, from Rydberg-atom arrays to multi-level encodings in neutral ytterbium atoms.
Representative papers: decoding measurement-prepared quantum phases and transitions, unifying emergent hydrodynamics and Lindbladian low-energy spectra, Landau-forbidden quantum criticality in Rydberg quantum simulators.
Topological band theory and correlated physics
We study the interplay of band topology and strong correlations, including the classification of topological bands with non-Hermitian Bloch Hamiltonians and their correspondence with Hermitian systems, and the correlated insulators, nematicity, and superconductivity of moiré materials such as twisted bilayer graphene, using both analytic approaches and sign-problem-free quantum Monte Carlo.
Representative papers: periodic table for topological bands with non-Hermitian Bernard-LeClair symmetries, spin-polarized correlated insulator and superconductor in twisted double bilayer graphene, fermionic Monte Carlo study of a realistic model of twisted bilayer graphene.
Exotic quantum phases and quantum criticality
Beyond the Landau paradigm, we look for phases and critical points characterized by emergent gauge fields and fractionalized excitations: deconfined quantum critical points in frustrated magnets such as the Shastry-Sutherland lattice, Dirac spin liquids, symmetry-enriched topological phases, emergent multi-flavor QED3, and gauge theories obtained by gauging modulated symmetries.
Representative papers: signatures of a deconfined phase transition on the Shastry-Sutherland lattice, evidence for a Z2 Dirac spin liquid, emergent multi-flavor QED3.