590 research outputs found
Berry-phase description of Topological Crystalline Insulators
We study a class of translational-invariant insulators with discrete
rotational symmetry. These insulators have no spin-orbit coupling, and in some
cases have no time-reversal symmetry as well, i.e., the relevant symmetries are
purely crystalline. Nevertheless, topological phases exist which are
distinguished by their robust surface modes. Like many well-known topological
phases, their band topology is unveiled by the crystalline analog of Berry
phases, i.e., parallel transport across certain non-contractible loops in the
Brillouin zone. We also identify certain topological phases without any robust
surface modes -- they are uniquely distinguished by parallel transport along
bent loops, whose shapes are determined by the symmetry group. Our findings
have experimental implications in cold-atom systems, where the crystalline
Berry phase has been directly measured.Comment: Latest version is accepted to PR
Holonomic Quantum Computing Based on the Stark Effect
We propose a spin manipulation technique based entirely on electric fields
applied to acceptor states in -type semiconductors with spin-orbit coupling.
While interesting in its own right, the technique can also be used to implement
fault-resilient holonomic quantum computing. We explicitly compute adiabatic
transformation matrix (holonomy) of the degenerate states and comment on the
feasibility of the scheme as an experimental technique.Comment: 5 page
Extracting Excitations From Model State Entanglement
We extend the concept of entanglement spectrum from the geometrical to the
particle bipartite partition. We apply this to several Fractional Quantum Hall
(FQH) wavefunctions on both sphere and torus geometries to show that this new
type of entanglement spectra completely reveals the physics of bulk quasihole
excitations. While this is easily understood when a local Hamiltonian for the
model state exists, we show that the quasiholes wavefunctions are encoded
within the model state even when such a Hamiltonian is not known. As a
nontrivial example, we look at Jain's composite fermion states and obtain their
quasiholes directly from the model state wavefunction. We reach similar
conclusions for wavefunctions described by Jack polynomials.Comment: 5 pages, 7 figures, updated versio
Wilson-Loop Characterization of Inversion-Symmetric Topological Insulators
The ground state of translationally-invariant insulators comprise bands which
can assume topologically distinct structures. There are few known examples
where this distinction is enforced by a point-group symmetry alone. In this
paper we show that 1D and 2D insulators with the simplest point-group symmetry
- inversion - have a classification. In 2D, we identify a relative
winding number that is solely protected by inversion symmetry. By analysis of
Berry phases, we show that this invariant has similarities with the first Chern
class (of time-reversal breaking insulators), but is more closely analogous to
the invariant (of time-reversal invariant insulators). Implications of
our work are discussed in holonomy, the geometric-phase theory of polarization,
the theory of maximally-localized Wannier functions, and in the entanglement
spectrum.Comment: The updated version is accepted in Physical Review
Matrix Product States for Trial Quantum Hall States
We obtain an exact matrix-product-state (MPS) representation of a large
series of fractional quantum Hall (FQH) states in various geometries of genus
0. The states in question include all paired k=2 Jack polynomials, such as the
Moore-Read and Gaffnian states, as well as the Read-Rezayi k=3 state. We also
outline the procedures through which the MPS of other model FQH states can be
obtained, provided their wavefunction can be written as a correlator in a 1+1
conformal field theory (CFT). The auxiliary Hilbert space of the MPS, which
gives the counting of the entanglement spectrum, is then simply the Hilbert
space of the underlying CFT. This formalism enlightens the link between
entanglement spectrum and edge modes. Properties of model wavefunctions such as
the thin-torus root partitions and squeezing are recast in the MPS form, and
numerical benchmarks for the accuracy of the new MPS prescription in various
geometries are provided.Comment: 5 pages, 1 figure, published versio
Bulk-Edge Correspondence in the Entanglement Spectra
Li and Haldane conjectured and numerically substantiated that the
entanglement spectrum of the reduced density matrix of ground-states of
time-reversal breaking topological phases (fractional quantum Hall states)
contains information about the counting of their edge modes when the
ground-state is cut in two spatially distinct regions and one of the regions is
traced out. We analytically substantiate this conjecture for a series of FQH
states defined as unique zero modes of pseudopotential Hamiltonians by finding
a one to one map between the thermodynamic limit counting of two different
entanglement spectra: the particle entanglement spectrum, whose counting of
eigenvalues for each good quantum number is identical (up to accidental
degeneracies) to the counting of bulk quasiholes, and the orbital entanglement
spectrum (the Li-Haldane spectrum). As the particle entanglement spectrum is
related to bulk quasihole physics and the orbital entanglement spectrum is
related to edge physics, our map can be thought of as a mathematically sound
microscopic description of bulk-edge correspondence in entanglement spectra. By
using a set of clustering operators which have their origin in conformal field
theory (CFT) operator expansions, we show that the counting of the orbital
entanglement spectrum eigenvalues in the thermodynamic limit must be identical
to the counting of quasiholes in the bulk. The latter equals the counting of
edge modes at a hard-wall boundary placed on the sample. Moreover, we show this
to be true even for CFT states which are likely bulk gapless, such as the
Gaffnian wavefunction.Comment: 20 pages, 6 figure
Haldane Statistics in the Finite Size Entanglement Spectra of Laughlin States
We conjecture that the counting of the levels in the orbital entanglement
spectra (OES) of finite-sized Laughlin Fractional Quantum Hall (FQH) droplets
at filling is described by the Haldane statistics of particles in a
box of finite size. This principle explains the observed deviations of the OES
counting from the edge-mode conformal field theory counting and directly
provides us with a topological number of the FQH states inaccessible in the
thermodynamic limit- the boson compactification radius. It also suggests that
the entanglement gap in the Coulomb spectrum in the conformal limit protects a
universal quantity- the statistics of the state. We support our conjecture with
ample numerical checks.Comment: 4.1 pages, published versio
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