Observation of Half-Quantum Vortices in an Exciton-Polariton Condensate

Lagoudakis, Konstantinos G.; Ostatnický, T.; Kavokin, A. V.; Rubo, Yuri G.; André, R.; Deveaud-Plédran, Benoît

doi:10.1126/science.1177980

Cited by 340 publications

(318 citation statements)

References 23 publications

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“…In the circular polarization basis, a HQV results in a full 2p phase shift in one polarization and no phase shift in the other. This feature significantly simplifies the detection method as we make use of a polarization mixing Mach-Zehnder interferometer 24 (see Methods section), in the mirrorretroreflector configuration (Fig. 1a).…”

Section: Resultsmentioning

confidence: 99%

“…Being the lowest energy topological excitations, they are essential in determining the Kosterlitz-Thouless phase transition in spinor quantum fluids 22 . Convincing experimental evidence of HQVs was recently provided in a spinor polariton condensate 24 , where the properties of the system allow for direct imaging of both the amplitude and phase of the condensate wave function. Signs of fractional vorticity were previously only reported in hightemperature superconductors 25 , later indirectly measured in spin-triplet superconductors 26 and identified as a result of the decay of 2D Skyrmions in atomic condensates 27 , while their observation is still elusive in other spinor systems like He3 thin films 28 .…”

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Dissociation dynamics of singly charged vortices into half-quantum vortex pairs

et al. 2012

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The quest for identification and understanding of fractional vorticity is a major subject of research in the quantum fluids domain, ranging from superconductors, superfluid Helium-3 to cold atoms. In a two-dimensional Bose degenerate gas with a spin degree of freedom, the fundamental topological excitations are fractional vortical entities, called half-quantum vortices. Convincing evidence for the existence of half-quantum vortices was recently provided in spinor polariton condensates. The half-quantum vortices can be regarded as the fundamental structural components of singly charged vortices but, so far, no experimental evidence of this relation has been provided. Here we report on the direct and time-resolved observation of the dynamical process of the dissociation of a singly charged vortex into its primary components, a pair of half-quantum vortices. The physical origin of the observed phenomenology is found in a spatially inhomogeneous static potential that couples the two spin components of the condensate.

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Section: Resultsmentioning

confidence: 99%

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Dissociation dynamics of singly charged vortices into half-quantum vortex pairs

et al. 2012

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“…Therefore, a fork-like defect in a phase pattern can be a signature of a quantized vortex. Fork-like defects in interference patterns were reported for optical vortices, see [45] and references therein, vortices in atom condensates [46][47][48], and polariton vortices [49,50].…”

Section: Phase Singularities: Fork-like Defects In Exciton Interferenmentioning

confidence: 96%

Spontaneous coherence in a cold exciton gas

High¹,

Leonard²,

Hammack³

et al. 2012

Nature

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Excitons, bound pairs of electrons and holes, form a model system to explore the quantum physics of cold bosons in solids. Cold exciton gases can be realized in a system of indirect excitons, which can cool down below the temperature of quantum degeneracy due to their long lifetimes. Here, we report on the measurement of spontaneous coherence in a gas of indirect excitons. We found that extended spontaneous coherence of excitons emerges in the region of the macroscopically ordered exciton state and in the region of vortices of linear polarization. The coherence length in these regions is much larger than in a classical gas, indicating a coherent state with a much narrower than classical exciton distribution in momentum space, characteristic of a condensate. We also observed phase singularities in the coherent exciton gas. Extended spontaneous coherence and phase singularities emerge when the exciton gas is cooled below a few Kelvin. Spontaneous coherence of excitonsIf bosonic particles are cooled down below the temperature of quantum degeneracy they can spontaneously form a coherent state in which individual matter waves synchronize and combine. Spontaneous coherence of matter waves forms the basis for a number of fundamental phenomena in physics, including superconductivity, superfluidity, and Bose-Einstein condensation (BEC) [1][2][3][4][5]. Spontaneous coherence is the key characteristic of condensation in momentum space [6].Excitons are hydrogen-like bosons at low densities [7] and Cooper-pair-like bosons at high densities [8]. The bosonic nature of excitons allows for condensation in momentum space, i.e. emergence of spontaneous coherence. Designing semiconductor structures with required characteristics and controlling the parameters of the exciton system gives an opportunity to study various types of exciton condensates.A condensate of exciton-polaritons was recently realized in semiconductor microcavities [9][10][11][12][13]. This condensate is characterized by a strong coupling of excitons to the optical field and a short lifetime of the polaritons. Unlike BEC, equilibrium is not required for the polariton condensation and coherence in the polariton condensate forms due to a coherent optical field similar to coherence in lasers [14].There are intriguing theoretical predictions for a range of coherent states in cold exciton systems, including BEC [7], BCS-like condensation [8], charge-density-wave formation [15], and condensation with spontaneous timereversal symmetry breaking [16]. In these condensates, spontaneous coherence of exciton matter waves emerges below the temperature of quantum degeneracy.Since excitons are much lighter than atoms, quantum degeneracy can be achieved in excitonic systems at temperatures orders of magnitude higher than the microKelvin temperatures needed in atomic vapors [1, 2]. Exciton gases need be cooled down to a few Kelvin to enter the quantum regime. Although the temperature of the semiconductor crystal lattice T lat can be lowered well below 1 K in He-refrigerators, lower...

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“…Their existence was first predicted in superfluids [1,2], and later in coherent waves [3]. Nowadays, quantised vortices have been the subject of extensive research across several areas of physics and have been observed in type-II superconductors, 4 He, ultracold atomic gases, non-linear optical media (for a review see, e.g., [4]) and very recently microcavity polaritons [5,6,7,8,9,10,11,12], the coherent strong mixing of a quantum well exciton with a cavity photon. adding a pulsed Gaussian probe to the OPO regime (the so called TOPO regime) in Sec.…”

Section: Introductionmentioning

confidence: 99%

Vortices in Polariton OPO Superfluids

Marchetti

Szymańska

2012

Exciton Polaritons in Microcavities

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This chapter reviews the occurrence of quantised vortices in polariton fluids, primarily when polaritons are driven in the optical parametric oscillator (OPO) regime. We first review the OPO physics, together with both its analytical and numerical modelling, the latter being necessary for the description of finite size systems. Pattern formation is typical in systems driven away from equilibrium. Similarly, we find that uniform OPO solutions can be unstable to the spontaneous formation of quantised vortices. However, metastable vortices can only be injected externally into an otherwise stable symmetric state, and their persistence is due to the OPO superfluid properties. We discuss how the currents charactering an OPO play a crucial role in the occurrence and dynamics of both metastable and spontaneous vortices.

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Observation of Half-Quantum Vortices in an Exciton-Polariton Condensate

Cited by 340 publications

References 23 publications

Dissociation dynamics of singly charged vortices into half-quantum vortex pairs

Dissociation dynamics of singly charged vortices into half-quantum vortex pairs

Spontaneous coherence in a cold exciton gas

Vortices in Polariton OPO Superfluids

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