Several different structures fabricated in GaAs with embedded InAs quantum dots
Quantum dots (QDs) coupled to photonic crystal nanocavities constitute a scalable, robust, on-chip semiconductor platform both for probing fundamental cavity quantum electrodynamics (CQED) as well as developing new technologies for classical and quantum information processing. These optical cavities give rise to field localization inside of sub-cubic wavelength volumes, which leads to a very large dipole-field interaction strength, with vacuum Rabi frequencies in the range of tens of gigahertz [1]. Such a strong light-matter interaction produces an optical nonlinearity that is present even at the single-photon level and is tunable at a very fast time scale [2]. This enables us to go beyond fundamental CQED studies and move toward fabricating potential devices for low-power optical information processing.
While much of the work in this system has been motivated by experiments done with cold atoms, our solid-state platform is distinguished from atomic CQED by the presence of an interesting phonon-assisted interaction between a quantum dot and a cavity [3-4], or between two quantum dots [5], even when they are detuned from each other by tens of cavity linewidths. This novel phenomenon demonstrates the richness of working in the solid-state platform, as well as its great potential for additional ways of controlling the QD-cavity interaction. In particular, such an "off-resonant coupling" can be employed to perform coherent quantum dot spectroscopy (as reading out the quantum dot state is of essential interest for building quantum gates), and to overcome the inhomogeneous broadening of quantum dots that has often been considered the main obstacle to scaling of single quantum dot-based systems.
Off-resonant coupling between two quantum dots in a photonic crystal cavity