Coherent photonic coupling of semiconductor quantum dots
ABSTRACT We report a new type of coupling between quantum dot excitons mediated by the strong single-photon field in a high-finesse micropillar cavity. Coherent exciton coupling is observed for two dots with energy differences of the order of the exciton-photon coupling. The coherent coupling mode is characterized by an anticrossing with a particularly large line splitting of 250 microeV. Because of the different dispersion relations with temperature, the simultaneous photonic coupling of quantum dot excitons can be easily distinguished from cases of sequential strong coupling of two quantum dots.
- Optics Letters 12/2006; 31(23):3507-3507. DOI:10.1364/OL.31.003507 · 3.18 Impact Factor
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ABSTRACT: The authors report on AlAs/GaAs micropillar cavities with unprecedented quality factors based on high reflectivity distributed Bragg reflectors (DBRs). Due to an increased number of mirror pairs in the DBRs and an optimized etching process record quality (Q) factors up to 165.000 are observed for micropillars with diameters of 4 μm. Optical studies reveal a very small ellipticity of 5×10−4 of the pillar cross section. Because of the high Q factors, strong coupling with a vacuum Rabi splitting of 23 μeV is observed for micropillars with a diameter of 3 μm.Applied Physics Letters 06/2007; 90:251109. DOI:10.1063/1.2749862 · 3.52 Impact Factor
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ABSTRACT: We study the detailed propagative characteristics of optical pulses in photonic band-gap (PBG) waveguides, coupled near resonantly to inhomogeneously broadened distributions of quantum dots. The line centers of the quantum-dot (QD) distributions are placed near a sharp discontinuity in the local electromagnetic density of states. Using finite-difference time-domain (FDTD) simulations of optical pulse dynamics and independent QD susceptibilities associated with resonance fluorescence, we demonstrate subpicosecond switching from pulse absorption to pulse amplification using steady-state optical holding and gate fields with power levels on the order of 1 milliwatt. In the case of collective response of QDs within the periodic dielectric microstructure, the gate power level is reduced to 200 microwatt for room temperature operation. In principle, this enables 200 Gbits per second optical information processing at wavelengths near 1.5 microns in various wavelength channels. The allowed pulse bandwidth in a given waveguide channel exceeds 0.5 THz allowing switching of subpicosecond laser pulses without pulse distortion. The switching contrast from absorption to gain is governed by the QD oscillator strength and dipole dephasing time scale. We consider dephasing time scales ranging from nanoseconds (low-temperature operation) to one picosecond (room-temperature operation). This all-optical transistor action is based on simple Markovian models of single-dot and collective-dot inversion and switching by coherent resonant pumping near the photon density of states discontinuity. The structured electromagnetic vacuum is provided by two-mode waveguide architectures in which one waveguide mode has a cutoff that occurs, with very large Purcell factor, near the QDs resonance, while the other waveguide mode exhibits nearly linear dispersion for fast optical propagation and modulation. Unlike optical switching based on Kerr nonlinearities in an optical cavity resonator, switching power levels and switching speeds for our QD device are not inversely proportional to cavity quality factors.Physical Review A 12/2007; 76(6). DOI:10.1103/PhysRevA.76.063814 · 2.99 Impact Factor