title: Vortex and half-vortex dynamics in a nonlinear spinor quantum fluid.
abstract: Vortices are archetypal objects that recur in the universe across the scale of complexity, from subatomic particles to galaxies and black holes. Their appearance is connected with spontaneous symmetry breaking and phase transitions. In Bose-Einstein condensates and superfluids, vortices are both point-like and quantized quasiparticles. We use a two-dimensional (2D) fluid of polaritons, bosonic particles constituted by hybrid photonic and electronic oscillations, to study quantum vortex dynamics. Polaritons benefit from easiness of wave function phase detection, a spinor nature sustaining half-integer vorticity, strong nonlinearity, and tuning of the background disorder. We can directly generate by resonant pulsed excitations a polariton condensate carrying either a full or half-integer vortex as initial condition and follow their coherent evolution using ultrafast imaging on the picosecond scale. The observations highlight a rich phenomenology, such as the spiraling of the half-vortex and the joint path of the twin charges of a full vortex, until the moment of their splitting. Furthermore, we observe the ordered branching into newly generated secondary couples, associated with the breaking of radial and azimuthal symmetries. This allows us to devise the interplay of nonlinearity and sample disorder in shaping the fluid and driving the vortex dynamics. In addition, our observations suggest that phase singularities may be seen as fundamental particles whose quantized events span from pair creation and recombination to 2D+t topological vortex strings.
authors.affiliation: Consiglio Nazionale delle Ricerche (CNR) NANOTEC, Istituto di Nanotecnologia, Via Monteroni, 73100 Lecce, Italy. ; Università del Salento, Dipartimento di Matematica e Fisica "Ennio de Giorgi," Via Arnesano, 73100 Lecce, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Dominici
authors.affiliation: Department of Physics, University of Warwick, CV47AL Coventry, UK.
authors.forename: Galbadrakh
authors.initials: G
authors.lastname: Dagvadorj
authors.affiliation: Department of Physics, University of Warwick, CV47AL Coventry, UK.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Fellows
authors.affiliation: Consiglio Nazionale delle Ricerche (CNR) NANOTEC, Istituto di Nanotecnologia, Via Monteroni, 73100 Lecce, Italy.
authors.forename: Dario
authors.initials: D
authors.lastname: Ballarini
authors.affiliation: Consiglio Nazionale delle Ricerche (CNR) NANOTEC, Istituto di Nanotecnologia, Via Monteroni, 73100 Lecce, Italy.
authors.forename: Milena
authors.initials: M
authors.lastname: De Giorgi
authors.affiliation: Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Francesca M
authors.identifier: 0000-0003-1394-7394
authors.initials: FM
authors.lastname: Marchetti
authors.affiliation: Dipartimento di Fisica, Università degli Studi di Napoli Federico II, 80126 Napoli, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Piccirillo
authors.affiliation: Dipartimento di Fisica, Università degli Studi di Napoli Federico II, 80126 Napoli, Italy.
authors.forename: Lorenzo
authors.identifier: 0000-0002-1154-8966
authors.initials: L
authors.lastname: Marrucci
authors.affiliation: Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, ENS-PSL, Research University, Collàge de France, 4 place Jussieu, case 74, F-75005 Paris, France.
authors.forename: Alberto
authors.initials: A
authors.lastname: Bramati
authors.affiliation: Consiglio Nazionale delle Ricerche (CNR) NANOTEC, Istituto di Nanotecnologia, Via Monteroni, 73100 Lecce, Italy. ; Università del Salento, Dipartimento di Matematica e Fisica "Ennio de Giorgi," Via Arnesano, 73100 Lecce, Italy.
authors.forename: Giuseppe
authors.identifier: 0000-0002-2583-5747
authors.initials: G
authors.lastname: Gigli
authors.affiliation: Department of Physics and Astronomy, University College London, WC1E6BT London, UK.
authors.forename: Marzena H
authors.initials: MH
authors.lastname: Szymańska
authors.affiliation: Consiglio Nazionale delle Ricerche (CNR) NANOTEC, Istituto di Nanotecnologia, Via Monteroni, 73100 Lecce, Italy.
authors.forename: Daniele
authors.identifier: 0000-0002-3831-8829
authors.initials: D
authors.lastname: Sanvitto
keywords: Bose Einstein condensates; Polaritons; nonlinearity; qunatum vortices; topological excitations