Polariton ring condensates and sunflower ripples in an expanding quantum liquid

Abstract

Optically pumping high quality semiconductor microcavities allows for the spontaneous formation of polariton condensates, which can propagate over distances of many microns. Tightly focussed pump spots here are found to produce expanding incoherent bottleneck polaritons which coherently amplify the ballistic polaritons and lead to the formation of unusual ring condensates. This quantum liquid is found to form a remarkable sunflower-like spatial ripple pattern which arises from self interference with Rayleigh-scattered coherent polariton waves in theČerenkov regime. PACS numbers: 71.36.+c, 42.65.Yj, 73.63.Hs, 78.67.De Condensing solid state bosonic quasiparticles brings prospects for macroscopic quantum-coherent integrated devices. Although still cryogenic, advances in coherent atom matter-wave optics [1,2] shows what might be possible with room temperature condensation, as sought for years with superconductors. In the last decade it has become apparent that polaritons formed from coupling semiconductor excitons with cavity photons produce bosonic quasiparticles that can condense [3,4], even at room temperature [6], with superfluid transport and a number of unusual vortex states now discussed [7][8][9].Polariton condensation requires high-Q optical cavities, large light-matter Rabi coupling exceeding thermal energies (hΩ > k B T ), and efficient relaxation into bosonic quasiparticles from the high-energy injected fermionic carriers. Successful condensation in microcavities made of III-V arsenides [3], II-VI tellurides [4], III-V nitrides [6, 10] and anthracene [11] have relied on natural spatial traps produced by the disordered energy landscape to confine polaritons sufficiently to initiate condensation, as well as artificially created ones. This is largely due to the existence of a 'bottleneck' [12] in the relaxation pathway where polaritons collect, thus forming a high-energy reservoir from which they cannot relax further. Condensation requires an additional localized concentration of the bosons. However such disorder-induced localization severely hampers development of chip-based condensate circuits.Here we demonstrate an efficient scheme to pump such non-equilibrium quantum liquids, that produces unusual coherent spatial ring states. These macroscopic condensate rings experience spatially-localized stimulated scattering as the bosons expand ballistically. Despite their outwards acceleration the quantum liquid remains phase coherent. We show that spatial ripples appearing as interferometric sunflowers arise from elastic scattering in the superfluid.The microcavities consist of a 5λ/2 AlGaAs cavity containing four sets of three GaAs quantum wells placed at the antinodes of the cavity electric field, surrounded by two AlGaAs/AlAs Bragg mirrors of 35 (bottom) and 32 (top) pairs. The cavity quality factor is measured to exceed Q>16000, with cavity photon lifetime τ c =9ps. Strong coupling is obtained with a Rabi splitting between lower and upper polariton energies of 9 meV. All data presented here use a negative...

Geometrically locked vortex lattices in semiconductor quantum fluids

“…2e) and DE c ¼ E c À E LPB , the condensate energy with respect to the bottom of the unperturbed lower polariton branch (LPB). Polaritons are created with k ¼ 0 at each pump spot and accelerate outwards through decreasing blueshifts at larger distances 12,13 , with D(r410 mm) ¼ 0. In the centre between the three pumped spots (spots centroid, O) the wavefunction is thus the superposition of three k o vectors at 1201 to each other, directed out from each pump spot (Supplementary Fig.…”

“…Polariton condensates have a finite lifetime and need to be constantly pumped, prompting extensive studies of the rich phenomena in out-of-equilibrium condensates 9 . This also makes it simple to shape the condensate flow [11][12][13] and sculpt the confinement potential [12][13][14] using the pump fields.…”

Quantum Langevin model for nonequilibrium condensation

“…First experimental evidence of condensation in spatially non-trivial modes was reported in [17] and discussed in [18]. More complicate spatial features were investigated in [37,50]. …”

Nonlinear interactions in an organic polariton condensate

“…3,4 On the other hand, the nonlinearity inherited from the exciton gives rise to the hydrodynamic behaviour of polaritons. 5,6, 7,8,9,10,11 Polaritons have a finite lifetime, determined principally by their photonic component, beyond which they decay through the cavity mirrors. If relaxation is efficient enough, however, a macroscopic population can be accumulated in a single state-often the ground state-via bosonic final state stimulation.…”