Twist of generalized skyrmions and spin vortices in a polariton superfluid

Abstract

We study the spin vortices and skyrmions coherently imprinted into an exciton-polariton condensate on a planar semiconductor microcavity. We demonstrate that the presence of a polarization anisotropy can induce a complex dynamics of these structured topologies, leading to the twist of their circuitation on the Poincaré sphere of polarizations. The theoretical description of the results carries the concept of generalized quantum vortices in two-component superfluids, which are conformal with polarization loops around an arbitrary axis in the pseudospin space.quantum vortices | topology | Poincaré space | condensates | polaritons T opological defects represent a wide class of objects relevant to different fields of physics from condensed matter to cosmology. The universality of monopoles, vortices, skyrmions, domain walls, and of their formation processes in different systems, has largely motivated their study in the condensed matter context. In particular, the interplay between the symmetry breaking in phase transitions and the formation of topological defects has been the focus of intensive research in the last century. In high-energy physics, the existence of an isolated point source intrigued a great number of physicists (1). Dirac was "surprised if Nature had made no use of it" and postulated the possibility of the magnetic monopoles linked to the quantization of electric charge (2). However, the elusiveness of their observation in free space has motivated an extensive study of monopole analogues in the form of quasiparticles in many-body systems (3) such as the exotic spin ices (4, 5), liquid crystals (6), exciton-polariton (7), and rubidium Bose-Einstein condensates (BECs) (8, 9), as well as other systems (10, 11). In a 2D multicomponent BEC, an equivalent topological structure to the monopole is given by the hedgehog polarization vortex (12), which together with the hyperspin vortex (13) belongs to the class of spin vortices that when combined lead to a well-defined polarization pattern. Such topological states are characterized by a linear polarization vector which rotates an integer number of times (spin winding number) around a singular central point, in a way analogous to what the magnetization does in the spin vortices of a ferromagnetic spinor BEC (14).In this work we excite complex vortex states in an excitonpolariton superfluid and study their amplitude, phase, and polarization dynamics. We demonstrate that temporal evolution of such topologies leads, in general, to a twist of the polarization plane in the Poincaré space. The observed features of the vortex behavior are explained within the concept of generalized spin vortices, where the rotation of polarization at large distances occurs around an arbitrary axis on the Poincaré sphere.Polaritons emerge in planar semiconductor microcavities as eigenmodes of the strong coupling regime between the exciton resonance and the photon cavity mode, combining the properties of light and matter. The photons confer on polaritons a very small effective mass (10...

Pulse, polarization and topology shaping of polariton fluids

“…In the specific, we realize a full Poincaré pattern such as the skyrmion, whose reshaping on time lengths of the order of the polariton lifetimes can be described as a twist in the polarization space and reveal a wide framework of generalized skyrmions and spin vortex states. 18 Again, the recent works we show here point to the large potentialities of microcavity polaritons and of their topological resonant excitation (e.g., associated to the presence of orbital angular momentum vortex states with non-trivial polarization textures), whose dynamical redistribution represents a polarization shaping approach fully exploitable in engineered microcavity devices.…”

“…Space structured topology such as full Poincaré skyrmion beams have be imprinted too and their reshaping described in the polarization space. 18 The most recent of our experiments and models are hence pushed further on, by empowering with the Rabi oscillations the ultrafast topology shaping of quantized vortices, as shown in the last section of this work. …”

“…At the intermediate time here shown (∼ 30 ps), noteworthy the S 2 and S 3 distributions in real • twist corresponds to a complete transmutation of the initial star skyrmion into its conjugate state (lemon skyrmion). The effect is discussed in Donati et al (2016). 18 The two left bottom panels (χ0 = 0.02 meV) show the additional effect of including the TE-TM splitting, which leads to a transverse shrinking and an azimuthal straining of the topological belt.…”

“…The effect is discussed in Donati et al (2016). 18 The two left bottom panels (χ0 = 0.02 meV) show the additional effect of including the TE-TM splitting, which leads to a transverse shrinking and an azimuthal straining of the topological belt. See also Video 1. http://dx.doi.org/10.1117/12.2250997.1 space have roughly exchanged with each other, with respect to initial time.…”

“…By means of polarization control of the incoming/outgoing pulse and tuning of the q-plate, we can set a specific superposition of two LG beams with integer or null phase winding in the two spin components: their combination is responsible for the resultant vector vortex beam. 72 One relevant field pattern that is possible to obtain, among the others, is the skyrmion (see 18 ), which we imprint on the photonic pulse and hence in the initial resonant polariton state. Upon specific conditions the skyrmion corresponds to the stereographic projection of the whole Poincaré sphere itself (see also 61 ), and it should be considered the full-Poincaré beam by excellence.…”