Polariton Laser Using Single MicropillarGaAs−GaAlAsSemiconductor Cavities

Abstract

Polariton lasing is demonstrated on the zero dimensional states of single GaAs/GaAlAs micropillar cavities. Under non resonant excitation, the measured polariton ground state occupancy is found to be as large as 10 4 . Changing the spatial excitation conditions, competition between several polariton lasing modes is observed, ruling out Bose-Einstein condensation. When the polariton state occupancy increases, the emission blueshift is the signature of self-interaction within the halflight half-matter polariton lasing mode.PACS numbers: 78.55. Et, 71.36.+c, 78.45.+h Boson statistics can lead to massive occupation of a single quantum state and trigger final state stimulation. This stimulation is responsible for the bright coherent emission of light in a laser. Another fascinating property of massive bosons in thermal equilibrium is their ability to accumulate in the lowest energy state under a given critical temperature. First predicted in 1925,[1] the experimental observation of Bose Einstein condensation was achieved in the mid 1990s for ultra-cold atoms. [2,3] Demonstrating such bosonic effects with matter waves in a solid state system is very interesting both from fundamental point of view but also for applications since it could provide a new source of coherent light. Cavity polaritons are an example of quasi-particles behaving as bosons at low density. [4,5] They are the exciton-photon mixed quasi-particles arising from the strong coupling regime between quantum well (QW) excitons and a resonant optical cavity mode. Because of their very small effective mass (10 −8 times that of the hydrogen atom) cavity polaritons are expected to condensate at unusually high temperatures (up to room temperature in wide band gap microcavities).[6] These last years, massive occupation of a polariton state has been observed in semiconductor two-dimensional (2D) cavities and attributed to Bose Einstein condensation [7,8] or to polariton lasing. [9] More recently, polariton condensation has been claimed in a localized energy trap [10] where the trap dimensions are sufficiently large for the system to present a 2D continuum of polariton states. In these experiments, the clear distinction of a thermodynamic phase transition (Bose Einstein condensation) from a kinetic stimulated scattering (polariton lasing) is still debated.In this letter, we demonstrate polariton lasing in micrometric sized GaAs/GaAlAs micropillar cavities. In such zero-dimensional (0D) cavities, polariton states are confined in all directions and present a well defined discretized energy spectrum. [11,12] The absence of translation invariance lifts the wave-vector conservation selection-rules in polariton scatterings. In GaAs 2D microcavities, these selection rules are responsible for inefficient polariton-phonon or polariton-polariton scattering, preventing the build-up of a large occupancy in the lower energy states. [13,14,15,16] In this work, we show that polariton scattering is very efficient in micropillar cavities. Under non resonant excitation, a thres...

Polaritronics in view

“…Tsintzos and colleagues' advance 2 builds on that, and fits in with a body of work [7][8][9] published in recent months. Two of these papers describe the construction of VCSEL-like cavities whose mirrors are of good enough quality to induce either electroluminescence 7 or the emission of laser light 8 in the polariton-coupling regime. Both these experiments were performed at temperatures of around 10 kelvin.…”

Macroscopic quantum self-trapping and Josephson oscillations of exciton polaritons

“…Its spectral width is 0.4 meV, which is larger than the bonding-antibonding splitting, thus allowing the preparation of a linear combination of both states 26 . Simultaneously, it is smaller than the energy separation between the ground state and the first excited state in a single micropillar 22 , and also smaller than the energy distance to the polariton reservoir (located 7.5 meV above). In our analysis we can thus ignore the excited states and only consider the ground state coupled modes.…”

“…1a) are obtained by dry etching of a planar semiconductor microcavity with a Rabi splitting of 15 meV at 10 K, the temperature of our experiments (see Methods). Each individual pillar has a diameter of 4 µm and presents a series of confined polaritonic states [21][22][23] with a lifetime τ ∼ 33 ps. The centre-to-centre separation of 3.7 µm results in a tunnel coupling of the lowest energy confined polaritonic states (ground state) of J = 0.1 meV.…”

Spontaneous formation and optical manipulation of extended polariton condensates

“…As compared with previously reported techniques to spatially confine polariton condensates 5,7,28,29 , the size and height of the trap can be continuously controlled by changing both the excitation power and the position of the spot. Controlling both the propagation and the wavefunction of a polariton condensate opens the way to the realization of polariton circuits, a first step towards high-speed all-optical information processing 22 .…”