330 research outputs found
Detecting edge degeneracy in interacting topological insulators through entanglement entropy
The existence of degenerate or gapless edge states is a characteristic
feature of topological insulators, but is difficult to detect in the presence
of interactons. We propose a new method to obtain the degeneracy of the edge
states from the perspective of entanglement entropy, which is very useful to
identify interacting topological states. Employing the determinant quantum
Monte Carlo technique, we investigate the interaction effect on two
representative models of fermionic topological insulators in one and two
dimensions, respectively. In the two topologically nontrivial phases, the edge
degeneracies are reduced by interactions but remain to be nontrivial.Comment: 6 pages, 4 figure
One-dimensional Quantum Spin Dynamics of Bethe String States
Quantum dynamics of strongly correlated systems is a challenging problem.
Although the low energy fractional excitations of one dimensional integrable
models are often well-understood, exploring quantum dynamics in these systems
remains challenging in the gapless regime, especially at intermediate and high
energies. Based on the algebraic Bethe ansatz formalism, we study spin dynamics
in a representative one dimensional strongly correlated model, {\it i.e. }, the
antiferromagnetic spin- XXZ chain with the Ising anisotropy, via
the form-factor formulae. Various excitations at different energy scales are
identified crucial to the dynamic spin structure factors under the guidance of
sum rules. At small magnetic polarizations, gapless excitations dominate the
low energy spin dynamics arising from the magnetic-field-induced
incommensurability. In contrast, spin dynamics at intermediate and high
energies is characterized by the two- and three-string states, which are
multi-particle excitations based on the commensurate N\'eel ordered background.
Our work is helpful for experimental studies on spin dynamics in both condensed
matter and cold atom systems beyond the low energy effective Luttinger liquid
theory. Based on an intuitive physical picture, we speculate that the dynamic
feature at high energies due to the multi-particle anti-bound state excitations
can be generalized to non-integrable spin systems.Comment: 15 pages, to appear in Phys. Rev.
New Environment Adaptation with Few Shots for OFDM Receiver and mmWave Beamforming
Few-shot learning (FSL) enables adaptation to new tasks with only limited
training data. In wireless communications, channel environments can vary
drastically; therefore, FSL techniques can quickly adjust transceiver
accordingly. In this paper, we develop two FSL frameworks that fit in wireless
transceiver design. Both frameworks are base on optimization programs that can
be solved by well-known algorithms like the inexact alternating direction
method of multipliers (iADMM) and the inexact alternating direction method
(iADM). As examples, we demonstrate how the proposed two FSL frameworks are
used for the OFDM receiver and beamforming (BF) for the millimeter wave
(mmWave) system. The numerical experiments confirm their desirable performance
in both applications compared to other popular approaches, such as transfer
learning (TL) and model-agnostic meta-learning
Revisiting Norm Regularized Optimization
Sparse optimization has seen its advances in recent decades. For scenarios
where the true sparsity is unknown, regularization turns out to be a promising
solution. Two popular non-convex regularizations are the so-called norm
and norm with , giving rise to extensive research on their induced
optimization. This paper explores norm regularized optimization in a
unified way for any . In particular, based on the proximal operator
of the norm, we establish the first-order and second-order optimality
conditions under mild assumptions. Then we integrate the proximal operator and
Newton method to develop a proximal Newton pursuit algorithm, followed by the
achievements of its global sequence convergence. Moreover, this is the first
paper maintaining the locally quadratic convergence rate for an algorithm
solving the norm regularization problem for any . The assumptions
to guarantee these results are relatively mild, In particular, there does not
necessarily need the strong smoothness. Finally, some numerical experiments
have demonstrated its high performance in comparison with several existing
leading solvers
Nonsymmorphic bosonization in one-dimensional generalized Kitaev spin-1/2 models
In this work, we perform a detailed study on the consequences of
nonsymmorphic symmetries in the Luttinger phase of the one-dimensional spin-1/2
Kitaev-Heisenberg-Gamma model with an antiferromagnetic Kitaev interaction.
Nonsymmorphic bosonization formulas for the spin operators are proposed,
containing ten non-universal coefficients which are determined by our density
matrix renormalization group simulations to a high degree of accuracy. Using
the nonsymmorphic bosonization formulas, different Fourier components and decay
powers in the correlation functions are disentangled, the response to weak
magnetic fields is analyzed, and the zigzag magnetic order in two dimensions is
recovered from a system of weakly coupled chains. We also find a line of
critical points with an emergent SU(2) conformal symmetry located on the
boundary of the Luttinger liquid phase, where a nonabelian version of
nonsymmorphic bosonization should be applied.Comment: 22 pages, 7 figure
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