Locally controlled photonic crystal devices with coupled quantum dots: physics and applications

Abstract

One of the most promising ways of building future nano-photonic networks for classical and quantum information processing is by using photonic crystals. Quantum dots coupled to optical modes allow for efficient control of light in these devices. In this dissertation I present the work I have done at Stanford University toward building integrated photonic crystal devices with coupled quantum dots. The most significant experiments that we performed on this platform relied on perfecting the fabrication techniques for photonic crystals, and developing technologies for local control of the cavity and quantum dot properties. In terms of fabrication, our lab is currently able to make state of the art GaAs photonic crystal cavities operating at the wavelength around 930nm with quality factors up to 25000. Combined with quantum dots, these cavities allowed us to achieve the strong coupling regime, which opened the possibility to perform fundamental experiments on cavity quantum electrodynamics. Regarding the local control of cavities and quantum dots, we have developed several techniques. Two of them relied on controlling the local temperature either via laser heating or micron-scale ohmic heaters. Another technique was based on in situ change of the index of refraction using chalcogenide glasses. Finally, we have also developed a method to control the quantum dot properties via a local electric field applied using metallic electrodes. The local temperature tuning played an essential role in the first experiments on coherent probing of strongly coupled cavity - quantum dot systems. The coherent probing technique enabled a series of fundamental experiments where the quantum dot in the cavity was used as a non-linear medium with an ultra-small mode volume. In one experiment, the phase of photons interacting with the system could be controlled via optical fields at power levels as low as one photon per characteristic lifetime of the system. Another experiment investigated quantum nonlinearities of the cavity - quantum dot system by demonstrating photon blockade and photon-induced tunneling. The great promise of using photonic crystals is that they can be combined in an integrated on-chip optical network. To this end, we have developed integrated devices that assemble resonators, waveguide, input/output couplers, and elements for local tuning. Single quantum dots were coupled to the resonators so they could act as on-chip light switches operating at the fundamental limit of light-matter interaction. For opto-electronic applications, the manipulation of light on a chip should be done either all optically or electrically. For electrical control we have developed techniques where the resonance of the quantum dot in the cavity is controlled by applying a lateral electric field using a metallic electrode. This switch has the promise to operate at energies per switching operation below 1 fJ, orders of magnitude lower than current state of the art devices. The goal is to extend this technique for waveguide-coupled cavities such that electro-optic switching can be implemented for on-chip optical signal processing.

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