Observation of second-order meron polarization textures in optical microcavities

Abstract

Multicomponent Bose–Einstein condensates, quantum Hall systems, and chiral magnetic materials display twists and knots in the continuous symmetries of their order parameters known as skyrmions. Originally discovered as solutions to the nonlinear sigma model in quantum field theory, these vectorial excitations are quantified by a topological winding number dictating their interactions and global properties of the host system. Here, we report the experimental observation of a stable individual second-order meron and antimeron appearing in an electromagnetic field. We realize these complex textures by confining light into a liquid-crystal-filled cavity that, through its anisotropic refractive index, provides an adjustable artificial photonic gauge field that couples the cavity photon motion to its polarization, resulting in the formation of these fundamental vectorial vortex states of light. Our observations could help bring topologically robust room-temperature optical vector textures into the field of photonic information processing and storage.

Annihilation of exceptional points from different Dirac valleys in a 2D photonic system

“…We note that in Ref. 28 , the very same structure was experimentally studied in the same regime of crossing between the N + 2 and N modes. The key difference is that the experiment was performed at higher detuning ∆, so that Fermi arcs were expected to be very small, below the grid size in k-space, and thus the EPs could not be resolved.…”

“…This splitting acts as photonic spin-orbit coupling characterized by a winding number 2 8,29 . The liquid crystal molecules orientation is set by an external voltage, which controls a tunable linear birefringence α 7,28 . A small birefringence α < (E N +1 − E N ) lifts the k = 0 degeneracy, leading to the formation of two tilted Dirac cones both carrying the same topological Berry charge 8 +1/2.…”

“…When α becomes comparable with (E N +1 − E N ), modes of different parities become energetically close and get coupled by a Rashba-Dresselhaus spin-orbit coupling with equal strength 7 , also called emergent optical activity 30 . Here we consider α ≈ (E N +2 − E N ) 28 , so that this optical activity is negligible. The corresponding eigenmodes look like two 2D parabola (Fig.…”

Liquid Crystalline Half‐Skyrmions and Their Optical Properties

“…Nevertheless, half-Skyrmions have attracted interest as an intriguing nontrivial texture exhibited by a system characterized by an orientational order parameter, and direct observation of half-Skyrmions has been realized in magnetic systems, [45,46] in accordance with the theoretical prediction. [30] Half-Skyrmions in antiferromagnetic systems [47] and photonic systems [48] are also gaining interest.…”

Optical excitations of Skyrmions, knotted solitons, and defects in atoms

“…2D baby-Skyrmions, like their 1D cousins [34], exhibit topologically non-trivial, non-singular configurations in reduced dimensions and have the best known early examples in superfluids as the Anderson-Toulouse-Chechetkin [35,36] and Mermin-Ho [37] non-singular vortices, owing to their ability to carry angular momentum. A large body of more recent research has included magnetic systems [38,39], with potential data storage applications, rotating atomic superfluids [40][41][42][43][44][45][46], exciton-polariton structures [47][48][49], and optical fields [50][51][52][53][54].…”