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Strong coupling in a single quantum dot–semiconductor microcavity system


Cavity quantum electrodynamics, a central research field in optics and solid-state physics1,2,3, addresses properties of atom-like emitters in cavities and can be divided into a weak and a strong coupling regime. For weak coupling, the spontaneous emission can be enhanced or reduced compared with its vacuum level by tuning discrete cavity modes in and out of resonance with the emitter2,4,5,6,7,8,9,10,11,12,13. However, the most striking change of emission properties occurs when the conditions for strong coupling are fulfilled. In this case there is a change from the usual irreversible spontaneous emission to a reversible exchange of energy between the emitter and the cavity mode. This coherent coupling may provide a basis for future applications in quantum information processing or schemes for coherent control. Until now, strong coupling of individual two-level systems has been observed only for atoms in large cavities14,15,16,17. Here we report the observation of strong coupling of a single two-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of about 140 µeV.

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Figure 1: Scanning electron micrographs of InGaAs QDs with different In contents before overgrowth.
Figure 2: Scanning electron micrograph and photoluminescence of processed microcavity pillars.
Figure 3: Temperature dependence of photoluminescence spectra for a 1.5-µm microcavity (Q = 7,350) showing the tuning of a single QD exciton through resonance with the cavity mode.
Figure 4: Dependences of photoluminescence peak energies, linewidths and integrated intensities on the temperature-generated energy shift of a reference QD for strong and weak coupling.


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Partial financial support of this work by the DARPA QuIST program, the Deutsche Forschungsgemeinschaft via Research Group Quantum Optics in Semiconductor Nanostructures, the Office of Naval Research and the ONR Nanoscale Electronics Program, INTAS and the State of Bavaria is acknowledged.

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Correspondence to A. Forchel.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Information

Contains supporting details of the sample technology as well as a discussion of the dot linewidth, the control of the in-plane dot position, single dot identification and the number of photons in a cavity at a given time. (DOC 26 kb)

Supplementary Figure 1

Schematic layer layout of the two-dimensional optical cavity. (PDF 18 kb)

Supplementary Figure 2

Temperature dependence of PL spectra for a 1.5 mm microcavity showing the tuning of a single QD exciton through resonance with the cavity mode in the weak coupling regime. (PDF 59 kb)

Supplementary Figure Legends

Legends to Supplementary Figures 1 and 2. (DOC 20 kb)

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Reithmaier, J., Sęk, G., Löffler, A. et al. Strong coupling in a single quantum dot–semiconductor microcavity system. Nature 432, 197–200 (2004).

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