33 research outputs found
Spin rings in bi-stable planar semiconductor microcavities
A unique feature of exciton-polaritons, inherited from their mixed
light-matter origin, is the strongly spin-dependent polariton-polariton
interaction, which has been predicted to result in the formation of spin rings
in real space [Shelykh et al., Phys. Rev. Lett. 100, 116401 (2008)]. Here we
experimentally demonstrate the spin bi-stability of exciton-polaritons in an
InGaAs-based semiconductor microcavity under resonant optical pumping. We
observe the formation of spin rings whose size can be finely controlled in a
spatial scale down to the micrometer range, much smaller than the spot size. We
additionally evaluate the sign and magnitude of the antiparallel polariton spin
interaction constant.Comment: 5 pages, 4 figure
Merging of vortices and antivortices in polariton superfluids
Quantised vortices are remarkable manifestations on a macroscopic scale of the coherent nature of
quantum fluids, and the study of their properties is of fundamental importance for the understanding
of this peculiar state of matter. Cavity-polaritons, due to their double light-matter nature, offer
a unique controllable environment to investigate these properties. In this work we theoretically
investigate the possibility to deterministically achieve the annihilation of a vortex with an antivortex
through the increase of the polariton density in the region surrounding the vortices. Moreover we
demonstrate that by means of this mechanism an array of vortex-antivortex pairs can be completely
washed out
Interaction-shaped vortex-antivortex lattices in polariton fluids
Topological defects such as quantized vortices are one of the most striking manifestations of the
superfluid nature of Bose-Einstein condensates and typical examples of quantum mechanical phenomena
on a macroscopic scale. Here we demonstrate the formation of a lattice of vortex-antivortex
pairs and study, for the first time, its properties in the non-linear regime at high polarion-density
where polariton-polariton interactions dominate the behaviour of the system. In this work first we
demonstrate that the array of vortex-antivortex pairs can be generated in a controllable way in terms
of size of the array and in terms of size and shape of it fundamental unit cell. Then we demonstrate
that polariton-polariton repulsion can strongly deform the lattice unit cell and determine the pattern
distribution of the vortex-antivortex pairs, reaching a completely new behaviour with respect
to geome
All -optical control of the quantum flow of a polariton condensate
Although photons in vacuum are massless particles that do not appreciably interact with each other, significant interactions appear in suitable nonlinear media, leading to hydrodynamic behaviours typical of quantum fluids(1-6). Here, we show the generation and manipulation of vortex-antivortex pairs in a coherent gas of strongly dressed photons (polaritons) flowing against an artificial potential barrier created and controlled by a light beam in a semiconductor microcavity. The optical control of the polariton flow allows us to reveal new quantum hydrodynamical phenomenologies such as the formation of vortex pairs upstream from the optical barrier, a case of ultra-short time excitation of the quantum flow, and the generation of vortices with counterflow trajectories. Additionally, we demonstrate how to permanently trap and store quantum vortices hydrodynamically generated in the wake of a defect. These observations are supported by time-dependent simulations based on the non-equilibrium Gross-Pitaevskii equation(7)
Polariton superfluids reveal quantum hydrodynamic solitons
A quantum fluid passing an obstacle behaves differently from a classical one.
When the flow is slow enough, the quantum gas enters a superfluid regime and
neither whirlpools nor waves form around the obstacle. For higher flow
velocities, it has been predicted that the perturbation induced by the defect
gives rise to the turbulent emission of quantised vortices and to the
nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in
a semiconductor microcavity, we report the transition from superfluidity to the
hydrodynamic formation of oblique dark solitons and vortex streets in the wake
of a potential barrier. The direct observation of these topological excitations
provides key information on the mechanisms of superflow and shows the potential
of polariton condensates for quantum turbulence studies.Comment: Published version with corrected colorbar scale for Fig. 3. Raw data
available as ancillary file
Half-solitons in a polariton quantum fluid behave like magnetic monopoles
Monopoles are magnetic charges, point-like sources of magnetic field.
Contrary to electric charges they are absent in Maxwell's equations and have
never been observed as fundamental particles. Quantum fluids such as spinor
Bose-Einstein condensates have been predicted to show monopoles in the form of
excitations combining phase and spin topologies. Thanks to its unique spin
structure and the direct optical control of the fluid wavefunction, an ideal
system to experimentally explore this phenomenon is a condensate of
exciton-polaritons in a semiconductor microcavity. We use this system to create
half-solitons, non-linear excitations with mixed spin-phase geometry. By
tracking their trajectory, we demonstrate that half-solitons behave as
monopoles, magnetic charges accelerated along an effective magnetic field
present in the microcavity. The field-induced spatial separation of
half-solitons of opposite charges opens the way to the generation of magnetic
currents in a quantum fluid.Comment: 19 pages, includes Supplmentary Informatio
Characterization of the dynamic friction of woven fabrics: Experimental methods and benchmark results
A benchmark exercise was conducted to compare various friction test set-ups with respect to the measured coefficients of friction. The friction was determined between Twintex®PP, a fabric of commingled yarns of glass and polypropylene filaments, and a metal surface. The same material was supplied to all benchmark participants and the test conditions were prescribed, making the used set-up the most important variable among the laboratories. Tests at ambient temperature as well as tests above the melting point of polypropylene are part of the benchmark, in order to determine both the dry and hydrodynamic friction characteristics. The dependency on sliding velocity, average pressure and temperature was investigated. Systematic differences are observed between the measurements obtained by the different set-ups, which are discussed and related to design characteristics of the devices. The values obtained in this benchmark are comparable and may serve as a reference to evaluate other friction set-ups. The paper concludes with guidelines for the design of a friction teste
Quantum information with semiconductor nanostructures
Integrated optoelectronic devices based on exciton-polaritons are very promising for quantum information, since they allow quantum optical effects as well as spin control and spin switching. Moreover the quantum fluid properties of exciton polaritons indicate that they are good candidates for quantum simulation.Published versio