Talks

Surface codes are a basic ingredient in topological quantum computation, but do not admit a universal set of topologically protected gates. In this talk I introduce group surface codes, which generalize the usual Z2 surface code to non-Abelian finite groups G. By identifying a simple labelling of the logical states, I will show that these codes admit transversal non-Clifford gates for suitable choices of G. I then discuss how to switch between Z2 and non-Abelian group surface codes to complete a universal gate set. This talk is based on work in preparation with Vieri Mattei, Apoorv Tiwari, and Tyler Ellison.

I will talk about the 1D quantum breakdown model in boson and spin systems, which has an exponential U(1) symmetry with charge decaying exponentially in space. We show that the ground state of the model exhibits a phase transition from a symmetric paramagnetic phase to a quantum breakdown condensate phase that spontaneously breaks the exponential U(1) symmetry. Unconventionally, the condensate phase does not have gapless Goldstone modes, making the spontaneous symmetry breaking stable at zero temperature in 1D. The condensate phase also has an exponentially large ground state degeneracy, which resembles a quantum glass but requires no disorder. This challenges the existing classification schemes of quantum phases of matter.

Gravitational waves (GW) offer a unique window into primordial density perturbations that may differ significantly from the adiabatic fluctuations observed in the CMB and large-scale structure. This raises an exciting prospect of seeing fluctuations of a completely new field from inflation in the anisotropy patterns of GW maps. However, CMB constraints impose an apparent tradeoff between distinctive anisotropy and sizable isotropic signal of such a GW background. I will show that rotating axion-like fields can naturally circumvent this limitation, producing both a strong GW background and large anisotropies within it. I will present the key characteristics of this signal and explore its detection prospects with future GW experiments.

Primordial non-Gaussianities (PNGs) are imprints in the density field caused by particle interactions during the inflationary epoch. A subclass of these signatures ("cosmological colliders") encode information about the interactions and properties of any additional particle fields present during inflation. I introduce a novel method for producing cosmological simulations with arbitrary collider signals, and present signatures from over thirty collider models in the deeply non-linear regime of the density field. I show how weak lensing surveys can offer competitive constraints that are complementary to other probes of PNGs in the late Universe. This simulation framework expands the probes of nonlinear structure (beyond lensing) that are usable in constraining primordial particle physics, which in turn expands the space of testable models and enhances the precision with which we constrain them.