41 research outputs found
Stabilization of zero-energy skin modes in finite non-Hermitian lattices
The zero energy of a one-dimensional semi-infinite non-Hermitian lattice with nontrivial spectral topology may disappear when we introduce boundaries to the system. While the corresponding zero-energy state can be considered as a quasi-edge state for the finite lattice with a long survival time, any small disruption (noise) in the initial form of the quasi-edge state can significantly shorten the survival time. Here, by tailoring the couplings at one edge we form an exceptional point allowing for a topological phase transition and the stabilization of the quasi-edge state in a finite-size lattice with open edges. Such a small modification in the lattice does not require closing and opening of the band gap and opens the door for experimental realization of such robust zero-energy edge states
Coexistence of extended and localized states in the one-dimensional non-Hermitian Anderson model
In one-dimensional Hermitian tight-binding models, mobility edges separating extended and localized states can appear in the presence of properly engineered quasiperiodical potentials and coupling constants. On the other hand, mobility edges do not exist in a one-dimensional Anderson lattice since localization occurs whenever a diagonal disorder through random numbers is introduced. Here we consider a nonreciprocal non-Hermitian lattice and show that the coexistence of extended and localized states appears with or without diagonal disorder in the topologically nontrivial region. We discuss that the mobility edges appear basically due to the boundary condition sensitivity of the nonreciprocal non-Hermitian lattice
Robust Exceptional Points in Disordered Systems
We construct a theory to introduce the concept of topologically robust
exceptional points (EP). Starting from an ordered system with elements, we
find the necessary condition to have the highest order exceptional point,
namely order EP. Using symmetry considerations, we show an EP
associated with an order system is very sensitive to the disorder.
Specifically, if the EP associated with the ordered system occurs at the fixed
degree of non-Hermiticity , the disordered system will not have EP
at the same which puts an obstacle in front of the observation
and applications of EPs. To overcome this challenge, by incorporating an
asymmetric coupling we propose a disordered system that has a robust EP which
is extended all over the space. While our approach can be easily realized in
electronic circuits and acoustics, we propose a simple experimentally feasible
photonic system to realize our robust EP. Our results will open a new direction
to search for topologically robust extended states (as opposed to topological
localized states) and find considerable applications in direct observation of
EPs, realizing topological sensors and designing robust devices for metrology
Dynamical Casimir Effect for a Swinging Cavity
The resonant scalar particle generation for a swinging cavity resonator in
the Casimir vacuum is examined. It is shown that the number of particles grows
exponentially when the cavity rotates at some specific external frequency.Comment: to appear in J. Phys. A: Math. Theo
Observation of Robust Zero Energy Extended States
Topological edge states arise at the interface of two topologically-distinct structures and have two distinct features: they are localized and robust against symmetry protecting disorder. On the other hand, conventional transport in one dimension is associated with extended states, which typically do not have topological robustness. In this paper, using lossy coupled resonators in one dimension, we demonstrate both theoretically and experimentally the existence of robust states residing in the bulk. We show that they are unusually robust against disorders in coupling between adjacent sites and losses. Our work paves the way to a new form of robust transport that is not limited to boundary phenomena and can be accessed more easily from far field