1,721,502 research outputs found
Delocalization of light in photonic lattices with unbounded potentials
No full textIn classical mechanics, a particle cannot escape from an unbounded potential well. Naively, one would expect a similar result to hold in wave mechanics, since high barriers make tunneling difficult. However, this is not always the case and it is known that wave delocalization can arise in certain models with incommensurate unbounded potentials sustaining critical states, i.e. states neither fully extended nor fully localized. Here we introduce a different and broader class of unbounded potentials, which are not quasi-periodic and do not require any specially-tailored shape, where wave delocalization is observed. The results are illustrated
by considering light dynamics in synthetic photonic lattices, which should provide a feasible platform for the experimental observation of wave delocalization in unbounded potentials.N
Robust Anderson transition in non-Hermitian photonic quasicrystals
No full textAnderson localization, i.e. the suppression of diffusion in lattices with random or incommensurate disorder, is a fragile interference phenomenon which is spoiled out in the presence of dephasing effects or fluctuating disorder. As a consequence, Anderson localization-delocalization phase transitions observed in Hermitian systems, such as in one-dimensional quasicrystals when the amplitude of the incommensurate potential is increased above a threshold, are washed out when dephasing effects are included. Here we consider localization-delocalization spectral phase transitions occurring in non-Hermitian quasicrystals with local incommensurate gain and loss, and show that, contrary to the Hermitian case, the non-Hermitian phase transition is robust against dephasing effects. The results are illustrated by considering synthetic quasicrystals in photonic mesh lattices.N
Non-Hermitian dynamical topological winding in photonic mesh lattices
No full textTopological winding in non-Hermitian systems is generally associated to the Bloch band properties of lattice Hamiltonians. However, in certain non-Hermitian models, topological winding naturally arises from the dynamical evolution of the system and is related to a new form of geometric phase. Here we investigate dynamical topological winding in non-Hermitian photonic mesh lattices, where the mean survival time of an optical pulse circulating in coupled fiber loops is quantized and robust against Hamiltonian deformations. The suggested photonic model could provide an experimentally accessible platform for the observation of non-Hermitian dynamical topological windings.Peer reviewe
Anderson localization in dissipative lattices
No full textAnderson localization predicts that wave spreading in disordered lattices can come to a complete halt, providing a universal mechanism for {dynamical localization}. In the one-dimensional Hermitian Anderson model with uncorrelated diagonal disorder, there is a one-to-one correspondence between dynamical localization and spectral localization, i.e. the exponential localization of all the Hamiltonian eigenfunctions. This correspondence can be broken when dealing with disordered dissipative lattices. Recently, it has been shown that when the system exchanges particles with the surrounding environment and random fluctuations of the dissipation are introduced, spectral localization is observed but without dynamical localization. Such previous studies considered lattices with mixed conservative (Hamiltonian) and dissipative dynamics, and were restricted to a semiclassical analysis. However, Anderson localization in purely dissipative lattices, displaying an entirely Lindbladian dynamics, remains largely unexplored. Here we consider the purely-dissipative Anderson model in the framework of a Lindblad master equation and show that, akin to the semiclassical models with conservative hopping and random dissipation, one observes dynamical delocalization in spite of strong spectral localization of all eigenstates of the Liouvillian superoperator. This result is very distinct than delocalization observed in the Anderson model with dephasing effects, where dynamical delocalization arises from the delocalization of the stationary state of the Liouvillian superoperator
Non-Hermitian dynamical topological winding in photonic mesh lattices
No full textTopological winding in non-Hermitian systems is generally associated to the Bloch band properties of lattice Hamiltonians. However, in certain non-Hermitian models, topological winding naturally arises from the dynamical evolution of the system and is related to a new form of geometric phase. Here we investigate dynamical topological winding in non-Hermitian photonic mesh lattices, where the mean survival time of an optical pulse circulating in coupled fiber loops is quantized and robust against Hamiltonian deformations. The suggested photonic model could provide an experimentally accessible platform for the observation of non-Hermitian dynamical topological windings.Agencia Estatal de Investigacion (MDM-2017-0711).N
Non-Hermitian Bloch-Zener phase transition
Full text linkBloch-Zener oscillations (BZO), i.e. the interplay between Bloch oscillations and Zener tunneling in two-band lattices under an external dc force, are ubiquitous in different areas of wave physics, including photonics. While in Hermitian systems such oscillations are rather generally aperiodic and only accidentally periodic, in non-Hermitian (NH) lattices BZO can show a transition from aperiodic to periodic as a NH parameter in the system is varied. Remarkably, the phase transition can be either smooth or sharp, contrary to other types of NH phase transitions which are universally sharp. A discrete-time photonic quantum walk on a synthetic lattice is suggested for an experimental observation of smooth BZO phase transitions
Dephasing-induced mobility edges in quasicrystals
No full text17 pages, 9 figures (main text + supplementary material), accepted for publication in the Physical Review Letters.Mobility edges (ME), separating Anderson-localized states from extended states, are known to arise in the single-particle energy spectrum of certain one-dimensional lattices with aperiodic order. Dephasing and decoherence effects are widely acknowledged to spoil Anderson localization and to enhance transport, suggesting that ME and localization are unlikely to be observable in the presence of dephasing. Here it is shown that, contrary to such a wisdom, ME can be created by pure dephasing effects in quasicrystals in which all states are delocalized under coherent dynamics. Since the lifetimes of localized states induced by dephasing effects can be extremely long, rather counter-intuitively decoherence can enhance localization of excitation in the lattice. The results are illustrated by considering photonic quantum walks in synthetic mesh lattices.N
Selective and tunable excitation of topological non-Hermitian skin modes
Full text linkNon-Hermitian lattices under semi-infinite boundary conditions sustain an
extensive number of exponentially-localized states, dubbed non-Hermitian skin
modes. Such states can be predicted from the nontrivial topology of the energy
spectrum under periodic boundary conditions via a bulk-edge correspondence.
However, the selective excitation of the system in one among the
infinitely-many topological skin edge states is challenging both from practical
and conceptual viewpoints. In fact, in any realistic system with a finite
lattice size most of skin edge states collapse and become metastable states.
Here we suggest a route toward the selective and tunable excitation of
topological skin edge states which avoids the collapse problem by emulating
semi-infinite lattice boundaries via tailored on-site potentials at the edges
of a finite lattice. We illustrate such a strategy by considering a
non-Hermitian topological interface obtained by connecting two Hatano-Nelson
chains with opposite imaginary gauge fields, which is amenable for a full
analytical treatment.Comment: 14 pages, 7 figures, under review by Proceedings of the Royal Society
Anderson localization without eigenstates in photonic quantum walks
No full textAnderson localization is ubiquitous in wavy systems with strong static and uncorrelated disorder. The delicate destructive interference underlying Anderson localization is usually washed out in the presence of temporal fluctuations or aperiodic drives in the Hamiltonian, leading to delocalization and restoring transport. However, in one-dimensional lattices with off-diagonal disorder Anderson localization can persist for arbitrary time-dependent drivings that do not break a hidden conservation law originating from the chiral symmetry, leading to the dubbed 'localization without eigenstates'. Here it is shown that such an intriguing phenomenon can be observed in discrete-time photonic quantum walks with static disorder applied to the coin operator, and can be extended to non-Hermitian dynamics as well
Robust Anderson transition in non-Hermitian photonic quasicrystals
Full text linkAnderson localization, i.e., the suppression of diffusion in lattices with a random or incommensurate disorder, is a fragile interference phenomenon that is spoiled out in the presence of dephasing effects or a fluctuating disorder. As a consequence, Anderson localization-delocalization phase transitions observed in Hermitian systems, such as in one-dimensional quasicrystals when the amplitude of the incommensurate potential is increased above a threshold, are washed out when dephasing effects are included. Here we consider localization-delocalization spectral phase transitions occurring in non -Hermitian (NH) quasicrystals with local incommensurate gain and loss and show that, contrary to the Hermitian case, the non -Hermitian phase transition is robust against dephasing effects. The results are illustrated by considering synthetic quasicrystals in photonic mesh lattices. (c) 2024 Optica Publishing Grou
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