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Controlling cavity reflectivity with a single quantum dot


Solid-state cavity quantum electrodynamics (QED) systems offer a robust and scalable platform for quantum optics experiments and the development of quantum information processing devices. In particular, systems based on photonic crystal nanocavities and semiconductor quantum dots have seen rapid progress. Recent experiments have allowed the observation of weak1 and strong coupling2,3 regimes of interaction between the photonic crystal cavity and a single quantum dot in photoluminescence. In the weak coupling regime1, the quantum dot radiative lifetime is modified; in the strong coupling regime3, the coupled quantum dot also modifies the cavity spectrum. Several proposals for scalable quantum information networks and quantum computation rely on direct probing of the cavity–quantum dot coupling, by means of resonant light scattering from strongly or weakly coupled quantum dots4,5,6,7,8,9. Such experiments have recently been performed in atomic systems10,11,12 and superconducting circuit QED systems13, but not in solid-state quantum dot–cavity QED systems. Here we present experimental evidence that this interaction can be probed in solid-state systems, and show that, as expected from theory, the quantum dot strongly modifies the cavity transmission and reflection spectra. We show that when the quantum dot is coupled to the cavity, photons that are resonant with its transition are prohibited from entering the cavity. We observe this effect as the quantum dot is tuned through the cavity and the coupling strength between them changes. At high intensity of the probe beam, we observe rapid saturation of the transmission dip. These measurements provide both a method for probing the cavity–quantum dot system and a step towards the realization of quantum devices based on coherent light scattering and large optical nonlinearities from quantum dots in photonic crystal cavities.

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Figure 1: Experiment set-up.
Figure 2: Photoluminescence of a single quantum dot tuned through strong coupling to a photonic crystal cavity.
Figure 3: Quantum dot–controlled cavity reflectivity at different probe wavelengths A–E, as indicated in Fig. 2b .
Figure 4: Quantum-dot-controlled cavity reflectivity versus probe beam power for probe laser detuning of Δ λ = -0.012 nm from the anticrossing point.


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Financial support was provided by the ONR Young Investigator Award, the MURI Center for photonic quantum information systems (ARO/DTO Program), the Okawa Foundation Faculty Research Grant, and the CIS Seed fund. D.E. and I.F. were also supported by the NDSEG fellowship. Work was performed in part at the Stanford Nanofabrication Facility of NNIN supported by the National Science Foundation.

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Correspondence to Jelena Vučković.

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Englund, D., Faraon, A., Fushman, I. et al. Controlling cavity reflectivity with a single quantum dot. Nature 450, 857–861 (2007).

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