4 research outputs found
Complete absorption of topologically protected waves
Chiral edge states can transmit energy along imperfect interfaces in a
topologically robust and unidirectional manner when protected by bulk-boundary
correspondence. However, in continuum systems, the number of states at an
interface can depend on boundary conditions. Here we design interfaces that
host a net flux of the number of modes into a region, trapping incoming energy.
As a realization, we present a model system of two topological fluids composed
of counter-spinning particles, which are separated by a boundary that
transitions from a fluid-fluid interface into a no-slip wall. In these fluids,
chiral edge states disappear, which implies non-Hermiticity and leads to a
novel interplay between topology and energy dissipation. Solving the fluid
equations of motion, we find explicit expressions for the disappearing modes.
We then conclude that energy dissipation is sped up by mode trapping. Instead
of making efficient waveguides, our work shows how topology can be exploited
for applications towards acoustic absorption, shielding, and soundproofing.Comment: 12 pages including Supplemental Material, 9 figures. See
https://www.youtube.com/watch?v=FoNgKH6GWJ4 for Supplementary Movi
An Exact Chiral Amorphous Spin Liquid
Topological insulator phases of non-interacting particles have been
generalized from periodic crystals to amorphous lattices, which raises the
question whether topologically ordered quantum many-body phases may similarly
exist in amorphous systems? Here we construct a soluble chiral amorphous
quantum spin liquid by extending the Kitaev honeycomb model to random lattices
with fixed coordination number three. The model retains its exact solubility
but the presence of plaquettes with an odd number of sides leads to a
spontaneous breaking of time reversal symmetry. We unearth a rich phase diagram
displaying Abelian as well as a non-Abelian quantum spin liquid phases with a
remarkably simple ground state flux pattern. Furthermore, we show that the
system undergoes a finite-temperature phase transition to a conducting thermal
metal state and discuss possible experimental realisations.Comment: 5 pages, 3 figure
Discovering quantum phase transitions with fermionic neural networks
Deep neural networks have been very successful as highly accurate wave function Ansätze for variational Monte Carlo calculations of molecular ground states. We present an extension of one such Ansatz, FermiNet, to calculations of the ground states of periodic Hamiltonians, and study the homogeneous electron gas. FermiNet calculations of the ground-state energies of small electron gas systems are in excellent agreement with previous initiator full configuration interaction quantum Monte Carlo and diffusion Monte Carlo calculations. We investigate the spin-polarized homogeneous electron gas and demonstrate that the same neural network architecture is capable of accurately representing both the delocalized Fermi liquid state and the localized Wigner crystal state. The network converges on the translationally invariant ground state at high density and spontaneously breaks the symmetry to produce the crystalline ground state at low density, despite being given no a priori knowledge that a phase transition exists
Neural Wave Functions for Superfluids
Understanding superfluidity remains a major goal of condensed matter physics.
Here we tackle this challenge utilizing the recently developed Fermionic neural
network (FermiNet) wave function Ansatz for variational Monte Carlo
calculations. We study the unitary Fermi gas, a system with strong,
short-range, two-body interactions known to possess a superfluid ground state
but difficult to describe quantitively. We demonstrate key limitations of the
FermiNet Ansatz in studying the unitary Fermi gas and propose a simple
modification that outperforms the original FermiNet significantly, giving
highly accurate results. We prove mathematically that the new Ansatz is a
strict generalization of the original FermiNet architecture, despite the use of
fewer parameters. Our approach shares several advantanges with the FermiNet:
the use of a neural network removes the need for an underlying basis set; and
the flexiblity of the network yields extremely accurate results within a
variational quantum Monte Carlo framework that provides access to unbiased
estimates of arbitrary ground-state expectation values. We discuss how the
method can be extended to study other superfluids.Comment: 14 pages, 5 figures. Talk presented at the 2023 APS March Meeting,
March 5-10, 2023, Las Vegas, Nevada, United State