Quantum Dot coupling engineering (and dynamic spin decoupling/deep nuclei cooling): 2-dimensional cluster state generation for quantum information processing

Project Information

QCEED

Grant agreement ID: 101185617

DOI

10.3030/101185617

EC signature date 25 October 2024

Start date 1 February 2025

End date 31 January 2029

Funded under

• The European Innovation Council (EIC)

Total cost

€ 3 013 180,00

EU contribution

€ 3 013 180,00

Coordinated by

UNIVERSITY COLLEGE CORK - NATIONAL UNIVERSITY OF IRELAND, CORK
Ireland

Periodic Reporting for period 1 - QCEED (Quantum Dot coupling engineering (and dynamic spin decoupling/deep nuclei cooling): 2-dimensional cluster state generation for quantum information processing)

Reporting period: 2025-02-01 to 2026-01-31

Summary of the context and overall objectives of the project

Quantum computation has enormous transformative potential for multiple industries, it is foreseen as enabling technology for many others. Building a practically useful quantum computer, however, is a formidable task, with scalability being the main bottleneck. Photonic quantum computing, where information is encoded in particles of light, offers a particularly promising scalable route. In practice, one of the key challenges of this approach is the lack of on-demand sources capable of generating large-scale entangled states of light required for universal quantum computation.

The QCEED project (Quantum Dot Coupling Engineering for 2-Dimensional Cluster State Generation) addresses this challenge by developing engineered semiconductor quantum dot systems capable of generating multidimensional photonic cluster states deterministically. These states are the resource for measurement-based quantum computing - a paradigm considered one of the most scalable and fault-tolerant approaches to quantum information processing.
The project focuses on overcoming current physical and technological limitations by (1) engineering coupled quantum dots with precisely controlled interactions required for multidimensional states generation, (2) exploiting advanced spin coherence enhancement techniques such as dynamic spin decoupling and nuclear cooling, (3) integrating quantum emitters into nanophotonic cavity architectures to enhance photon extraction efficiency, and (4) developing theoretical and experimental frameworks to validate scalable entanglement generation.

By exploring high-risk, high-gain concepts in semiconductor nanotechnology and quantum optics, and operating at low technology readiness levels (TRL 1-3), the project aims to establish the physical and technological foundations necessary for future integrated photonic quantum processors.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the initial phase, the consortium established coordinated theoretical, growth, spectroscopy, and nanofabrication workflows across two complementary platforms – (1) pyramidal site-controlled and (2) nanowire-based vapor-liquid-solid quantum dots.

First, advanced fabrication protocols were developed to create vertically stacked quantum dots with controlled separation and composition, aiming to realise a very specific energetic structure, where the quantum dots interact only through excited states. For pyramidal quantum dots, systematic studies identified regimes of independent and interacting quantum dot states, guided by newly developed theoretical models. For nanowire-based quantum dots, material composition tuning enabled wavelength control and significant reduction of emission linewidths, improving optical quality and device reproducibility.

Theoretical efforts delivered symmetry-adapted computational models capable of accurately describing electronic and excitonic states in both single and coupled pyramidal quantum dots. These models identified promising coupling pathways mediated by excited light-hole-like states, which is a distinctive feature of pyramidal quantum dots, providing direct guidance for experimental design. Similarly, coupling routes were identified for nanowire-based quantum dots.

Advanced cryogenic spectroscopy played a central role in validating growth outcomes and probing quantum dot coupling mechanisms. Resonant and polarization-resolved measurements of pyramidal quantum dots confirmed the presence of excited state mediated interactions and established optical benchmarks for further optimisation.

In parallel, early-stage development of cavity-compatible fabrication processes was initiated. Sacrificial layer growth and nanopost processing workflows were established to enable future integration of pyramidal quantum dots into broadband photonic cavities.

These combined advances position QCEED to progress toward controlled generation of entangled photonic states in subsequent project phases.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

So far, QCEED delivered early but significant advances in the controlled engineering of coupled quantum dots. A key result is the combined theoretical-experimental identification of excited light-hole-like valence-band states in [111]-oriented pyramidal quantum dots and their role in mediating inter-dot coupling. While coupling effects in stacked quantum dots have been studied previously, the identification and experimental validation of coupling pathways mediated by light-hole-like excited states represent a distinctive feature of this platform. This mechanism provides an experimentally accessible route to engineering inter-dot interactions in a controlled manner.

In parallel, improvements in nanowire-based quantum dot structures led to a substantial reduction in emission linewidths and enhanced photon extraction efficiency, addressing key material quality limitations observed in earlier device generations.

These results establish experimentally validated coupling regimes and material control strategies that extend the available design space for scalable quantum dot-based photonic systems.