Gain-Induced Trapping of Microcavity Exciton Polariton Condensates

Abstract

In this letter, we present a study of the condensation of exciton-polaritons in large etched pillar structures that exhibit shallow edge trapping. The ≈ 100 µm ×100 µm pillars were fabricated using photolithography and a BCl 3 /Cl 2 reactive ion etch. A low energy region emerged along the etched edge, with the minima ≈ 7 µm from the outer edge. The depth of the trap was 0.5 − 1.5 meV relative to the level central region, with the deepest trapping at the corners. We were able to produce a Bose-Einstein condensate in the trap near the edges and corners by pumping non-resonantly in the middle of the pillar. This condensate began as a set of disconnected condensates at various points along the edges, but then became a single mono-energetic condensate as the polariton density was increased. Similar edge traps could be used to produce shallow 1D traps along edges or other more complex traps using various etch geometries and scales. In the past two decades, many experiments have used polaritons resulting from strong coupling between trapped microcavity photons and quantum well (QW) excitons. These bosonic particles have a very light mass (∼ 10 −4 m e) due to being partially photonic, but also strong particle-particle interactions from being partially excitonic. 1 This combination of a light mass and strong interactions leads to the formation of Bose-Einstein con-densates (BECs) at relatively high temperatures (∼ 10 K). 2-4 Polaritons provide a promising system for studying bosonic particles at even higher temperatures, and polariton lasing has been observed at room temperature in both GaN 5 and organic 6 systems. Many methods of confinement have been used to study polariton dynamics in a variety of geometries. Applying stress to a thin (≈ 100 µm) GaAs sample can be used to shift the exciton energy, resulting in a harmonic trap. 4,7 Pumping such a stress trap non-resonantly in the center forms a repulsive barrier and can be used to form a ring geometry. 8 Complex pumping geometries can also be used to confine polaritons, including the use of two or more pump spots in various arrangements or using a ring-shaped pump spot. 9-13 More permanent methods of confinement include producing a spacer in certain regions of the cavity during the growth process, 14-16 using sub-wavelength gratings as the top mirror, 17,18 depositing metal strips onto the top mirror, 19 and etching the sample after growth to form 1D wires, 2D pillars, and 2D arrays of coupled pillars. 20-25 While optically induced trapping potentials have the advantage of being easily reconfigured, etched trapping allows the confinement to be somewhat independent of the pump laser. Post-growth etching also produces much higher potential barriers at the etched edges than the a) Electronic mail: dmm154@pitt.edu b) J. K. Wuenschell is now at Physical Sciences Laboratory, The Aerospace Corporation, El Segundo, CA 90245, USA deposition of metal strips, and it is compatible with our existing sample materials and growth methods, unlike sub-wavelength gratings or modulating t...

Single vortex–antivortex pair in an exciton-polariton condensate

“…multimode pump laser modulate the reservoir population strongly, this results in modulation of the local interaction energy and thus of the local phase of the condensate, which induces a separation of the vortex and antivortex. We confirmed that a vortex-antivortex pair is not regularly generated when a quiet single-mode pump laser is used 22 . We also note that thermal effects are not strong enough to spontaneously create a vortex-antivortex pair in our system.…”

“…The incident power is controlled by a polarization filtering set-up employing a variable retarder, as in ref. 22. The threshold power of 20 mW (see Supplementary Information) gives a threshold particle density of ∼10 2 µm −2 for our 20-µm-diameter pumping spot, given the 4 ps lower-polariton lifetime, and estimated pumping efficiency of 15%.…”

“…The vortex pair is found to migrate perpendicular to its dipole moment and, in our experimental parameter space, recombines before reaching the condensate edge (see Supplementary Information). Despite the short polariton lifetime, a vortex pair survives for a long enough time to be observed.Our experiment is carried out in a GaAs-based microcavity sample 21,22 . The pump laser at above bandgap energy creates free electon-hole pairs, which form excitons and finally relax towards the lower polariton branch, as shown in the schematic of Fig.…”

“…Our experiment is carried out in a GaAs-based microcavity sample 21,22 . The pump laser at above bandgap energy creates free electon-hole pairs, which form excitons and finally relax towards the lower polariton branch, as shown in the schematic of Fig.…”

Localization and self-trapping in driven-dissipative polariton condensates

“…Such oscillations also occur in the dissipationdominated regime, where they reflect the coexistence of two condensates of different frequencies, as in a multimode laser [19]. Indeed at the qualitative level many important phenomena, like gap solitons [14,15], vortices [16], and condensate localization [17,24,25], occur in both interaction-dominated and dissipation-dominated condensates.…”