Quantum Dot Spin State Tailoring for Scalable On-Chip Quantum Information Processing

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A successful implementation of a fault tolerant quantum computer based on solid state spin qubits will most likely involve their arrangement in a regular lattice. Recent technological breakthroughs have enabled the creation of such scalable quantum systems with one of the most prominent being the platform of site-controlled quantum dots. The high spectral quality, deterministic positioning and all-optical ultrafast addressability of long lived spins in these quantum emitters, make them very attractive candidates as a platform for quantum hardware. Although there are several proposals that attempt to address the issue of inhomogeneous broadening in view of enabling scalable interactions within such hardware, here we will focus on the particular needs of a new hybrid approach that uses microcavity polaritons as a bus for information. This approach is based on spin dependent interactions between spin polarized exciton polaritons and the spins in quantum dots. For this approach to work, it is therefore necessary to engineer the spin states so that there are spin-spin interactions in the hybrid system while also maintaining optical addressability of the qubits. In this project we will investigate various approaches for on-demand engineering of the trapped spin states in charged quantum dots through a series of coherent control experiments that will explore how the different approaches affect the performance of all-optically operated universal single qubit gates. The samples that we will investigate initially are self-assembled InGaAs quantum dots with delta doping for charging while at a later stage we will investigate substrate nanopatterned and nanoimprint lithography site-controlled quantum dots, provided by our national and international collaborators. Based on the performance of our gates and the understanding of the limitations that we will gain from this project, we will then design a series of hybrid samples for an optimized hybrid polaritonic quantum dot system working closely with our national and international collaborators that specialize in the growth of this type of nanostructures. This project will therefore lay the groundwork for the realization of the novel hybrid approach for scalable on-chip quantum information processing. This heavily experimental project will contribute towards the development of a magnetic spectroscopy experiment with coherent control capabilities. Using this setup we will address and characterize both the self-assembled and site-controlled quantum dot samples by means of high resolution magneto-spectroscopic studies at liquid helium temperatures, while for the characterization of the performance of the universal single qubit quantum gates the work will involve advanced all-optical spin control techniques utilizing a combination of pulsed and CW lasers.