Karl Franzens University Graz
Graz University of Technology
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Karl Franzens University Graz | Graz University of Technology | |
Nanophotonics: Opportunities and Challenges Spontaneous emission is very fundamental and is often regarded as an inherent property of an excited atom, molecule or quantum dot. However, this view overlooks the fact that it is not only a property of the emitter, but of the combined emitter - vacuum system. The irreversibility of spontaneous emission comes about due to the infinite number of vacuum states available to the emitted photon. If the photonic environment is modified, for instance by placing the emitter within a cavity, spontaneous emission can be inhibited, enhanced or even made to become reversible. For semiconductor quantum dots in high finesse nano-cavities a wide range of novel optoelectronic devices have been realized using such cavity QED phenomena. Examples include high efficiency single photon sources, low-threshold, high bandwidth nanocavity lasers and even single-quantum dot optical components like mirrors and phase shifters. All such single-quantum dot cavity quantum QED devices call for a method to precisely control the spectral detuning between the quantum dots and the cavity mode. Until now this has been done by slowly tuning the lattice temperature or by condensing inert-gases at low temperatures. A major drawback of both of these methods is that they are slow, rendering them impractical for future single-quantum dot devices. In this talk I will describe how by electrically contacting single-quantum dot photonic crystal nanocavities, the dot-cavity detuning can be rapidly and reversibly switched over ~4 meV using the quantum confined Stark effect. In the weak-coupling regime of cavity quantum electrodynamics we observe a voltage switchable Purcell effect as well as non-resonant coupling that is active even when the dot and cavity mode are strongly detuned. For cavities with Q>10000 we observe strong coupling with vacuum Rabi splittings up to ~130 μeV, representing a voltage switchable single photon non-linearity. Our techniques could be readily extended to realize on-chip photonic crystal single-quantum dot optoelectronic devices with modulation bandwidths in the GHz range. This may pave the way towards the realization of on-chip, coherent single-quantum dot quantum photonic devices. |