N. A. Wasley

Interfacing Spins in an InGaAs Quantum Dot to a Semiconductor Waveguide Circuit Using Emitted Photons

eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website.

Restoring mode degeneracy in H1 photonic crystal cavities by uniaxial strain tuning

We demonstrate a uniaxial strain technique to tune the mode wavelengths of planar photonic crystal cavities. With experiments and numerical simulations, we show that it is possible to use an externally applied strain to control the splitting of the modes of the H1 cavity with high precision. By using this technique, we restore degeneracy to the fundamental modes of an H1 cavity which are initially split by ∼0.5 nm, thus demonstrating unpolarized emission at ∼950 nm with a quality factor of ∼3300.

III-V quantum light source and cavity-QED on silicon.

Non-classical light sources offer a myriad of possibilities in both fundamental science and commercial applications. Single photons are the most robust carriers of quantum information and can be exploited for linear optics quantum information processing. Scale-up requires miniaturisation of the waveguide circuit and multiple single photon sources. Silicon photonics, driven by the incentive of optical interconnects is a highly promising platform for the passive optical components, but integrated light sources are limited by silicons indirect band-gap. III–V semiconductor quantum-dots, on the other hand, are proven quantum emitters. Here we demonstrate single-photon emission from quantum-dots coupled to photonic crystal nanocavities fabricated from III–V material grown directly on silicon substrates. The high quality of the III–V material and photonic structures is emphasized by observation of the strong-coupling regime. This work opens-up the advantages of silicon photonics to the integration and scale-up of solid-state quantum optical systems.

Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities

We demonstrate semiconductor quantum dots coupled to photonic crystal cavity modes operating in the visible spectrum. We present the design, fabrication, and characterization of two dimensional photonic crystal cavities in GaInP and measure quality factors in excess of 7500 at 680 nm. We demonstrate full control over the spontaneous emission rate of InP quantum dots and by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode we observe a Purcell enhancement of ∼8.

Optical control of the emission direction of a quantum dot

Using the helicity of a non-resonant excitation laser, control over the emission direction of an InAs/GaAs quantum dot is demonstrated. The quantum dot is located off-center in a crossed-waveguide structure, such that photons of opposite circular polarization are emitted into opposite waveguide directions. By preferentially exciting spin-polarized excitons, the direction of emission can therefore be controlled. The directional control is quantified by using the ratio of the intensity of the light coupled into the two waveguides, which reaches a maximum of ±35%.

Integrated photonic devices with single quantum dots

The integration of InAs quantum dots as on-chip single-photon sources in GaAs photonic circuits is reviewed. A Hanbury Brown-Twiss effect is demonstrated using a monolithic directional coupler, together with coherent emission under resonant excitation.

GaAs integrated quantum photonic circuits

GaAs provides a versatile platform for developing on-chip integrated quantum-optical circuits. In this paper we review progress in developing spin-photon interfaces, on-chip beam-splitters and coherent single photon sources based on GaAs photonics.

Direct In-plane Readout of QD Spin

The results presented in Chap. 4 describe a crossed waveguide device in which the two transitions of a Zeeman split doublet located at the intersection couple approximately equally to all four waveguides. This is the expected behaviour of the device in which in-plane polarisation transfer was demonstrated by reconstruction of the full spin state by combining the output from two orthogonal waveguides. This device will be henceforth referred to as Device-A.

Development of Additional Technological Approaches

The development of quantum optical circuits provides an opportunity to study novel systems and quantum phenomena as yet not fully understood. However, the development of functional and controllable systems requires a range of technology to facilitate the integration of a large, and ever increasing, number of components. The purpose of the technology is to produce circuits that are inherently forgiving to the limitations of the fabrication that is currently available by providing a degree of tunability and control to a number of aspects in these systems.

InP QDs in GaInP Photonic Crystal Cavities

For certain applications the emission wavelength of InAs QDs (900–1,300 nm) is not ideal, as it is far from the maximum efficiency of commercially available Si based detectors. InP QDs embedded in GaInP provide an alternative with the significant advantage of emitting in the red spectral range, at the maximum efficiency of Si detectors.