Multi-qubit quantum photonic devices: Towards the emergent quantum internet

The future is quantum.
Quantum technology is envisioned to play a pivotal role in addressing global challenges, with recent decades witnessing remarkable advancements in quantum computation and communication. From simple demonstrations of single-qubit to sophisticated error-corrected multi-qubit gates surpassing their non-error-corrected counterparts, our community has come far. Quantum-based communication systems have revolutionized security standards worldwide, relying on efficient light-matter interfaces and robust quantum key distribution protocols. Recent proof-of-principle demonstrations of device-independent protocols mark a significant step towards a global quantum network. Quantum technology is so close to the brink of technological singularity.

My research focuses on the application of nanowire crystal-phase quantum dots as versatile quantum photonic devices, applicable in quantum computing, quantum memory, and quantum network nodes. Crystal-phase quantum dots are engineered through controlled crystal structure alternation between zincblende and wurtzite phases in III-V nanowires, with our current research efforts primarily focusing on GaAs. Since the quantum dot is formed purely by atomic layer stacking of the same material composition, the demarcation between two segments are atomically sharp, and it is impossible to have alloy content fluctuation that is commonplace in regular self-assembled quantum dots. The type-II band alignment between these phases enables spatially separated confinement of electrons and holes, allowing coupling of electrons localized on adjacent quantum dots via a shared excited state.

To harness these structures effectively, I performed comprehensive electronic state simulations based on k · p perturbation theory, complemented by calculations of quantum optical properties for various transitions. Correlated study between structure and optical properties is the focus of the final part of my PhD. I developed a method to transfer nanowires onto a transmission electron microscope grid, which enables the exact nanowires studied by photoluminescence to be examined, such that the presence and dimensions of crystal-phase quantum dots can be identified.

Building on this foundation, I studied quantum dynamics in crystal-phase quantum dot arrays, introducing novel location qubits native to these structures. A quantum optical control scheme based on Λ-type three-level system dynamics is proposed for quantum gate implementation, with theoretical performance analysis presented for both the location qubits and the optical quantum gates. To enable experimental demonstration, a specialized laser system was jointly developed by me and my fellow PhD Rohan Indran Radhakrishnan to generate, synchronize, and delay laser pulses with tunable sidebands for qubit preparation, manipulation and measurement. Beyond practical applications, my research also covers the investigation of fundamental fermionic physics, exploring the feasibility of using crystal-phase quantum dot arrays to examine entanglement properties in many-fermion systems. This work has significant implications for fermionic quantum computing and quantum chemical simulations, positioning crystal-phase quantum dots as a promising platform for advancing quantum technology on many frontiers.