Abstract Editor's Choice of this issue is the article by D. Schwedt et al. [1] on high resolution measurements of resonance fluorescence spectra from GaAs quantum wells. In the cover picture, the authors point out the connection between the experimental data and the model of disordered excitons. The lower left part shows a series of polarized photoluminescence spectra, fitted with very good agreement by a model of statistically distributed three‐level‐systems. The upper right part images the excitation mechanism. Only those excitons of an inhomogeneous distribution (indicated by the blue line) contribute to the resonance fluorescence (red line) which overlap spectrally with the monochromatic laser. It could be verified experimentally that the resonance fluorescence exhibits two parts: delta‐like Rayleigh scattering and Lorentzian luminescence. Daniel Schwedt is working in the DFG research group 'Quantum Optics in Semiconductor Nanostructures' and concentrates on quantum optical experiments on III–V semiconductor quantum well structures.
Abstract Editor's Choice of this issue is the article by D. Schwedt et al. [1] on high resolution measurements of resonance fluorescence spectra from GaAs quantum wells. In the cover picture, the authors point out the connection between the experimental data and the model of disordered excitons. The lower left part shows a series of polarized photoluminescence spectra, fitted with very good agreement by a model of statistically distributed three‐level‐systems. The upper right part images the excitation mechanism. Only those excitons of an inhomogeneous distribution (indicated by the blue line) contribute to the resonance fluorescence (red line) which overlap spectrally with the monochromatic laser. It could be verified experimentally that the resonance fluorescence exhibits two parts: delta‐like Rayleigh scattering and Lorentzian luminescence. Daniel Schwedt is working in the DFG research group 'Quantum Optics in Semiconductor Nanostructures' and concentrates on quantum optical experiments on III–V semiconductor quantum well structures.
Summary form only given. After the first observation of resonance scattering from excitons in quantum wells about 1980, this topic has received much interest and has given rise to a hot debate on the origin of this scattering process. Recently, the determination of the temporal behaviour and the coherence properties of this scattering has initiated revival of interferometric techniques in semiconductor optics. Finally, the observation of speckles in the angular distribution proved that this scattering indeed originates from exciton states localized by disorder. However, complementary information on the nature of the excitons and the interplay between scattering and luminescence can be obtained from high resolution cw spectroscopy, having the advantage that only a small fraction of the states within the homogeneous linewidth is excited. However yhe polarization behaviour is quite different for the coherent Rayleigh component and the luminescence, depending on the orientation, splitting and relaxation of the localized states. The experimental results for a 20 nm wide GaAs quantum well clearly confirm this prediction.
In this paper by Wolfgang Langbein and Jørn M. Hvam [1], selected as Editor's Choice in the present issue of phys. stat. sol. (a), the localization of biexcitonic and excitonic states in GaAs quantum wells is investigated by spectrally resolved four-wave mixing (FWM) experiments. The cover picture is a contour plot of the FWM intensity as a function of temporal pulse separation τ12 for cross-linear and co-polarization, scaled with the exciton binding energy R*y. Data are shown for three single and multi quantum well structures with different thicknesses, causing varying homogeneous and inhomogeneous broadening of the excitonic transitions (for details see [1]). The paper is an invited presentation and part of the Proceedings of the International Workshop on “Physics of Light–Matter Coupling in Nitrides (PLMCN-1)” held in Rome, Italy, September 26–29, 2001.
In this paper by Wolfgang Langbein and Jørn M. Hvam [1], selected as Editor's Choice in the present issue of phys. stat. sol. (a), the localization of biexcitonic and excitonic states in GaAs quantum wells is investigated by spectrally resolved four-wave mixing (FWM) experiments. The cover picture is a contour plot of the FWM intensity as a function of temporal pulse separation τ12 for cross-linear and co-polarization, scaled with the exciton binding energy R*y. Data are shown for three single and multi quantum well structures with different thicknesses, causing varying homogeneous and inhomogeneous broadening of the excitonic transitions (for details see [1]). The paper is an invited presentation and part of the Proceedings of the International Workshop on “Physics of Light–Matter Coupling in Nitrides (PLMCN-1)” held in Rome, Italy, September 26–29, 2001.
Single photon emission is one of the most striking optical properties of semiconductor quantum dots (QDs), and the corresponding photon anti-bunching effect was observed by photoluminescence experiments in single QDs under non-resonant excitation [1], and more recently under strictly resonant excitation of the fundamental interband transition [2,3]. This configuration minimizes the residual excitation of the QD environment that acts as a fluctuating reservoir for spectral diffusion [4], and thus allows the generation of indistinguishable photons [3]. In this paper, we report on the resonant fluorescence of the charged exciton of a single InAs/GaAs QD embedded in a planar microcavity [2]. We show in figure 1(a) the photoluminescence spectrum of a single QD with two lines X and CX that are identified as the neutral and charged excitons by auto- and cross-correlation measurements of the g(2) function, in (b,c) and (d) respectively. Fig.2 shows the resonant Rayleigh scattering spectra as a function of the laser detuning with the neutral (a) and charged (b) exciton lines. For X, we fit the spectrum with two Lorentzian lines of width 10¹eV and separated by 12.5¹eV which corresponds to the fine structure splitting. For CX, we observe a line that demonstrates the existence of residual charge carriers even if the laser is tuned in resonance with the lowest excitation of the QD, and its larger width of 40¹eV suggests spectral diffusion dephasing. References [1] P. Michler,A. Kiraz,C. Becher, W. V. Schoenfeld, P. M. Petroff, L. Zhang, E. Hu, and A. Imamoglu, Science 290 2282 (2000). [2] A. Muller, E. B. Flagg, P. Bianucci, X. Y. Wang, D. G. Deppe, W. Ma, J. Zhang, G. J. Salamo, M. Xiao, and C. K. Shih, Phys. Rev. Lett. 99 187402 (2007). [3] S. Ates, S. M. Ulrich, S. Reitzenstein, A. Lffler, A. Forchel, and P. Michler, Phys. Rev. Lett. 103 167402 (2009). [4] A. Berthelot, I. Favero, G. Cassabois, C. Voisin, C. Delalande, Ph. Roussignol, R. Ferreira, and J. M. Grard, Nature Physics 2 759 (2006).
Single photon emission is one of the most striking optical properties of semiconductor quantum dots (QDs), and the corresponding photon anti-bunching effect was observed by photoluminescence experiments in single QDs under non-resonant excitation [1], and more recently under strictly resonant excitation of the fundamental interband transition [2,3]. This configuration minimizes the residual excitation of the QD environment that acts as a fluctuating reservoir for spectral diffusion [4], and allows the generation of indistinguishable photons [3]. In this paper, we report on the resonant fluorescence of the neutral exciton in single InAs/GaAs QDs embedded in a planar microcavity [2]. We show in figure 1(a) the resonant Rayleigh scattering (RRS) spectrum as a function of the laser detuning with the neutral exciton line. We observe two Lorentzian lines of width 4μeV, separated by 9μeV and corresponding to two linear orthogonal polarizations, as expected for the fine structure splitting. We show in figure 1(b) a clear photon anti-bunching under strictly resonant excitation that proves that the RRS spectrum is dominated by resonant fluorescence of the neutral exciton. This situation is only rarely observed. The most frequent case corresponds to no resonance in the RRS spectrum and to a doublet in the non-resonant photoluminescence (PL) spectrum as shown in figure 2(a). The two lines are identified as the neutral and charged excitons by auto- and cross-correlation measurements of the g(2)(τ) function, as illustrated in figure 2(b). Strikingly, we observe the charged exciton line in the PL excitation spectrum of the neutral exciton line (figure 2(c)). This effect reveals the existence of residual charge carriers in the QD environment even under strictly resonant excitation. This favors incoherent population transfer between the charged and neutral excitons that competes with the coherent RRS effect and most frequently suppresses the resonant fluorescence of the neutral exciton. We conclude that the optical response of the QD remains affected by its environment even in case of coherent resonant pumping. [1] P. Michler, A. Kiraz, C. Becher, W. V. Schoenfeld, P. M. Petroff, L. Zhang, E. Hu, and A. Imamoglu, Science 290, 2282 (2000) [2] A. Muller, E. B. Flagg, P. Bianucci, X. Y. Wang, D. G. Deppe, W. Ma, J. Zhang, G. J. Salamo, M. Xiao, and C. K. Shih, Phys. Rev. Lett. 99, 187402 (2007) [3] S. Ates, S. M. Ulrich, S. Reitzenstein, A. Löffler, A. Forchel, and P. Michler, Phys. Rev. Lett. 103, 167402 (2009) [4] A. Berthelot, I. Favero, G. Cassabois, C. Voisin, C. Delalande, Ph. Roussignol, R. Ferreira, and J. M. Gérard, Nature Physics 2, 759 (2006)