Spin orbit coupling and the many body physics of rhombohedral graphene
Rhombohedral graphenes host van Hove singularities near the band edge which have been found to host magnetism and superconductivity. These systems have no no moire superlattice, and a ballistic mean free path far exceeding device dimensions, allowing precise measurements of the interplay of different symmetry breaking orders, including a cascade of half- and quarter metals with broken spin and/or valley symmetry as well as both spin-singlet and spin-triplet superconducting states. I will provide an overview of the physics of these systems, focusing on some r
Topological Kondo effects in mesoscopic systems
Abstract: I will discuss mesoscopic topological superconductors that can be used to realize quantum impurity models with orthogonal or symplectic symmetries. The first one uses a topological superconductor that hosts many (M>2) Majorana zero modes. Such an "M-Majorana island" coupled to normal metal leads realizes a novel type of topological Kondo effect, where the effective impurity "spin" transforms under the orthogonal group SO(M) stemming from the non-local topological ground state degeneracy of the island.
Exciton Condensates Through the Years
Abstract: Excitons are composite Bosons formed by pairing electrons and holes in a crystal.The idea that excitons might Bose condense dates to the 1960’s but has often been surrounded by controversy. My talk will focus on the important lessons learned
about exciton condensates from work on two-dimensional electron systems in the
quantum Hall regime, starting around twenty years ago, and on new opportunities
Vortex Majorana modes in trivial and topological superconductors
Abstract: In this talk, I will describe two distinct strategies for trapping Majorana zero modes (MZMs) with superconducting vortices. There exists a common belief that for s-wave superconductors, the existence of normal-state band topology, such as the topological Dirac surface state, is crucial for inducing vortex MZMs. We recently uncovered a striking example where nontrivial vortex Majorana physics arises in a trivial s-wave superconductor with a trivial normal state.
Dr. Maissam Barkeshli (UMD) Discrete shift and quantized charge polarization: New topological invariants and quantized response of crystalline topological states
When: December 6th at 11amWhere: ATL 4402Speaker: Dr. Maissam Barkeshli (UMD)Title: Discrete shift and quantized charge polarization: New topological invariants and quantized response of crystalline topological states
Error Mitigation Thresholds in Noisy Quantum Circuits
Abstract: Noise in quantum devices can be corrected with quantum error correction or it can be mitigated via classical post-processing. The latter can be done with negligible overhead in the space-time volume of the quantum circuit, but will generally incur exponential overhead in sampling complexity. We use statistical-mechanical arguments to discuss the limits of error mitigation in quantum circuits. We show that noisy random quantum circuit models with imperfectly characterized noise remain robust to imperfections at a finite rate of disorder, before exhibiting a diso
Subtleties in chiral anomalies and time crystals – a progress report
Abstract: I will discuss two topics that I have been collaborating on in CMTC. The first involves a careful study of an analog of the chiral anomaly in one dimension that was motivated by work from the Galitski group at Maryland which showed that the response of the chiral charge to electromagnetic fields could be affected by interactions. At the same time, the chiral anomaly, when it arises at boundaries of topological phases, is known to be associated with topological terms that cannot be renormalized.
Spin chains, defects, and quantum wires for the quantum-double edge
Abstract: Non-Abelian defects that bind Majorana or parafermion zero modes are prominent in several topological quantum computation schemes. Underpinning their established understanding is the quantum Ising spin chain, which can be recast as a fermionic model or viewed as a standalone effective theory for the surface-code edge -- both of which harbor non-Abelian defects. We generalize these notions by deriving an effective Ising-like spin chain describing the edge of quantum-double topological order.
Exotic exciton phases and quantum spin liquids in quantum Hall bilayer and moire bilayer
Abstract: In this talk I will discuss some exotic phases of excitons beyond the conventional exciton condensation phase. (1) In the first part, I will consider a coulomb coupled quantum Hall bilayer at filling (1/3,-1/3). (Equivalently (1/3,2/3)) and then tune d/l_b.