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Register a new userDissipative Topological Defects in Coupled Laser Networks
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Topologically protected defects have been observed and studied in a wide range of fields, such as cosmology, spin systems, cold atoms and optics as they are quenched across a phase transition into an ordered state. Revealing their origin and control is becoming increasingly important field of research, as they limit the coherence of the system and its ability to approach a fully ordered state. Here, we present dissipative topological defects in a 1-D ring network of phase-locked lasers, and show how their formation is related to the Kibble-Zurek mechanism and is governed in a universal manner by two competing time scales of the lasers, namely the phase locking time and synchronization time of their amplitude fluctuations. The ratio between these two time scales depends on the system parameters such as gain and coupling strength, and thus offers the possibility to control the probability of topological defects in the system. Enabling the system to dissipate to the fully ordered, defect-free state can be exploited for solving hard combinatorial optimization problems in various fields. As opposed to unitary systems where quenching is obtained via external cooling mostly through the edges, our dissipative system is kept strictly uniform even for fast quenches.
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The dynamics of dissipative topological defects in a system of coupled phase oscillators, arranged in one and two-dimensional arrays, is numerically investigated using the Kuramoto model. After an initial rapid decay of the number of topological defects, due to vortex-anti-vortex annihilation, we identify a long-time (quasi) steady state where the number of defects is nearly constant. We find that the number of topological defects at long times is significantly smaller when the coupling between the oscillators is increased at a finite rate rather than suddenly turned on. Moreover, the number of topological defects scales with the coupling rate, analogous to the cooling rate in KibbleZurek mechanism (KZM). Similar to the KZM, the dynamics of topological defects is governed by two competing time scales: the dissipation rate and the coupling rate. Reducing the number of topological defects improves the long time coherence and order parameter of the system and enhances its probability to reach a global minimal loss state that can be mapped to the ground state of a classical XY spin Hamiltonian.
Edge modes in topological insulators are known to be robust against defects. We investigate if this also holds true when the defect is not static, but varies in time. We study the influence of defects with time-dependent coupling on the robustness of the transport along the edge in a Floquet system of helically curved waveguides. Waveguide arrays are fabricated via direct laser writing in a negative tone photoresist. We find that single dynamic defects do not destroy the chiral edge current, even when the temporal modulation is strong. Quantitative numerical simulation of the intensity in the bulk and edge waveguides confirms our observation.
A rich variety of specific multidomain textures recently observed in antiferromagnetically coupled multilayers with perpendicular anisotropy include regular (equilibrium) multidomain states as well as different types of topological magnetic defects. Within a phenomenological theory we have classified and analyzed the possible magnetic defects in the antiferromagnetic ground state and determine their structures. We have derived the optimal sizes of the defects as functions of the antiferromagnetic exchange, the applied magnetic field, and geometrical parameters of the multilayer. The calculated magnetic phase diagrams show the existence regions for all types of magnetic defects. Experimental investigations of the remanent states (observed after different magnetic pre-history) in [Co/Pt]/Ru multilayers with wedged Co layers reveal a corresponding succession of different magnetic defect domain types.
Bosons hopping across sites and interacting on-site are the essence of the Bose-Hubbard model (BHM). Inspired by the success of BHM simulators with atoms in optical lattices, proposals for implementing the BHM with photons in coupled nonlinear cavities have emerged. Two coupled semiconductor microcavities constitute a model system where the hopping, interaction, and decay of exciton polaritons --- mixed light-matter quasiparticles --- can be engineered in combination with site-selective coherent driving to implement the driven-dissipative two-site optical BHM. Here we explore the interplay of interference and nonlinearity in this system, in a regime where three distinct density profiles can be observed under identical driving conditions. We demonstrate how the phase acquired by polaritons hopping between cavities can be controlled through effective polariton-polariton interactions. Our results open new perspectives for synthesizing density-dependent gauge fields for polaritons in two-dimensional multicavity systems.
Electromagnetic topological insulators have been explored extensively due to the robust edge states they support. In this work, we propose a topological electromagnetic system based on a line defect in topologically nontrivial photonic crystals (PCs). With a finite-difference supercell approach, modal analysis of the PCs structure is investigated in detail. The topological line-defect states are pseudospin polarized and their energy flow directions are determined by the corresponding pseudospin helicities. These states can be excited by using two spatially-symmetric line-source arrays carrying orbital angular momenta. The feature of the unidirectional propagation is demonstrated and it is stable when disorders are introduced to the PCs structure.
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