Talks

I will discuss the phenomenology of superconductors hosting both order parameter vortices and fractionally charged anyon excitations. I will demonstrate that in such systems superconductivity and topological order are intertwined under applied magnetic fields, leading to surprising observable consequences departing from traditional superconductivity from electronic pairing. In particular,  I will show that vortices nucleated by perpendicular magnetic fields must trap anyons in their cores. However, because only some vortices can trap an integer number of anyons, this places a constraint on the vortex phase winding. In general, rather than the expected hc/2e quantization of superconducting vortices, we find instead the enhanced flux quantum of hc/e, which I will argue should affect a wide range of observables. I will further develop a general Landau-Ginzburg theory describing vortex fluctuations and discuss the phase diagram as perpendicular magnetic field is increased, showing that condensation of the intertwined vortices leads to exotic insulating phases hosting neutral anyons and a nonvanishing thermal Hall effect.

I will present a unified framework for understanding the statistics and anomalies of excitations—ranging from particles to higher-dimensional objects—in quantum lattice systems. We introduce a general method to compute the quantized statistics of Abelian excitations in arbitrary dimensions via Berry phases of locality-preserving symmetry operations, uncovering novel statistics for membrane excitations. These statistics correspond to quantum anomalies of generalized global symmetries and imply obstructions to gauging, enforcing long-range entanglement. In particular, we show that anomalous higher-form symmetries enforce intrinsic long-range entanglement, meaning that fidelity with any SRE states must exhibit exponential decay, unlike ordinary (0-form) symmetry anomalies. As an application, we identify a new example of (3+1)D mixed-state topological order with fermionic loop excitations, characterized by a breakdown of remote detectability linked to higher-form symmetry anomalies.

In this talk, we will look at a general framework to design and analyze algorithms for the problem of testing homomorphisms between finite groups in the low-soundness regime.

Based on an upcoming joint work with Sourya Roy, University of Iowa.

Expanders are well-connected graphs that have been extensively studied and have numerous applications in computer science, including error-correcting codes. High-dimensional expanders (HDXs) generalize expanders to hypergraphs and have the powerful local-to-global property. Roughly speaking, this property states that the expansion of an HDX can be certified by the expansion of certain local structures. This property has made HDXs crucial in the recent breakthrough on locally testable codes (LTCs) [Dinur et al.'22]. These LTCs simultaneously achieve constant rate, constant relative distance, and constant query complexity. However, despite these desirable properties, these LTCs have yet to find applications in proof systems, as they lack the crucial multiplication property present in widely used polynomial codes. A major open question is: Do there exist LTCs with the multiplication property that achieve the same rate, distance, and query complexity as those constructed by Dinur et al.?

In this talk, I will provide intuition behind the connection between HDXs and LTCs, explain why the LTCs by Dinur et al. lack the multiplication property, and discuss my recent and ongoing work on constructing LTCs with the multiplication property. This talk is based on joint work with Irit Dinur, Huy Tuan Pham, and Rachel Zhang.

In recent years there is a growing interest in higher dimensional random complexes, both as natural extensions of random graphs, and as potential tools for new applications, e.g. to higher dimensional expanders. We will focus on two models of random complexes and their generic topological properties:

1. A classical theorem of Alon and Roichman asserts that the Cayley graph C(G,S) of a group G with respect to a logarithmic size random subset S of G is a good expander. We consider a k-dimensional analogue of Cayley graphs, called Balanced Cayley Complexes, discuss the spectral gap of their (k-1)-Laplacian and in particular obtain a high dimensional version of the Alon-Roichman theorem.

2. A permutation complex is the order complex of the intersection of two linear orders. We describe some properties of these complexes and discuss bounds on the probability that a permutation complex associated with random orders is topologically k-connected.
Joint work with Omer Moyal.

The coboundary expansion property of tensor product codes, also known as product expansion, plays an important role in the discovery of good quantum LDPC codes and classical locally testable codes. Prior research has shown that this property is equivalent to agreement testability and robust testability for products of two codes with linear distance. However, for products of more than two codes, it is a strictly stronger property.

In this talk, I will outline key ideas underlying a recent result establishing that tensor products of an arbitrary number of random codes over sufficiently large fields exhibit strong coboundary expansion. This result suggests promising directions for new quantum locally testable code constructions.

In this talk, we will introduce interactive oracle proofs (IOPs), which are an interactive generalization of probabilistically-checkable proofs (PCPs). IOPs can then be “compiled” into very efficient cryptographic proofs, which can be very short (say, polylogarithmic length) and admit very efficient verifiers (say, polylogarithmic time). One requirement that arises from practice is that the prover also be very efficient; ideally, running in linear time.

After introducing these concepts, I will outline how one can use error-correcting codes with efficient encoding algorithms to design efficient cryptographic proofs. We will then discuss Repeat-Accumulate-Accumulate (RAA) codes, which are a simple class of turbo codes offering extremely efficient encoding and near-GV bound minimum distance. We will spend a good portion of this presentation describing these codes, discussing the challenges which arise in their analysis, and surveying some open problems.