Quantum technology with a spin-photon architecture for thousand-qubit chipsets at telecom wavelengths

Project Information

QuSPARC

Grant agreement ID: 101186889

DOI

10.3030/101186889

EC signature date 8 November 2024

Start date 1 April 2025

End date 31 March 2028

Funded under

• The European Innovation Council (EIC)

Total cost

€ 2 998 646,00

EU contribution

€ 2 992 374,75

Coordinated by

OESTERREICHISCHE AKADEMIE DER WISSENSCHAFTEN
Austria

Periodic Reporting for period 1 - QuSPARC (Quantum technology with a spin-photon architecture for thousand-qubit chipsets at telecom wavelengths)

Reporting period: 2025-04-01 to 2026-03-31

Summary of the context and overall objectives of the project

Quantum information processing provides a view towards computations that are not feasible using classical machines. However, the creation of quantum systems with thousands to millions of physical qubits is currently understood to be an absolute necessity for the achievement of a practically relevant quantum advantage. The ambition to create such a system is hampered in traditional approaches by numerous physical and conceptual constraints, in particular regarding the connectivity of large-scale systems. In QuSPARC, we are developing a platform which can overcome all limits to scalability by leveraging unique aspects of spin centres in crystals within a photonic architecture. The electronic and nuclear spins in the centres act as the information storage and processing elements ("qubits") of the architecture, while the connectivity between them is provided by photonic links. The connectivity is achieved by adapting highly developed systems and methods from the optical telecommunication industry, including low-loss optical fibers, photonic integrated circuits (PICs), and high-precision micro-optical components. In order to make use of these tools, we focus our efforts on spin centres with optical transition wavelengths in the telecommunication range (1.26 µm - 1.68 µm). In particular, QuSPARC aims to utilize defects in crystalline silicon carbide (SiC), a material which has gained significant adoption in the semiconductor industry, as spin centres, guaranteeing a clear path towards large-scale industrial processing.

The core objectives of QuSPARC are to:

• Create a wafer-scale technology platform supporting thousands of quantum bits
• Develop high-fidelity spin initialization and measurement on qubit registers
• Demonstrate site-to-site connectivity, on and between chips

In order to achieve these goals, the consortium are building a scalable system consisting of fiber-coupled, individually tunable microcavities containing SiC membranes. The chip stack is designed to include spin control using superconducting wires for spin control with low heat dissipation. The coupling fibers will then link to PICs which allow switching and routing of the photons for joint projective measurements on separate sites. This approach allows to build a modular system in which connections between sites on a single device and those on other chips can be linked using a the same photonic network.
While the project is initially geared towards vanadium defects in 4H-SiC, the physical architecture is suitable for any spin centre with a telecom transition, and several candidate systems are currently under scrutiny within QuSPARC.
Furthermore, the approach is amenable to the implementation of higher-dimensional quantum systems ("qudits"). Such systems are of interest for the implementation of protection against errors in the quantum states and for higher density of quantum information per physical element of the register. These aspects, as well as the microscopic properties of the spin centres, form an important part of the project's theoretical research.

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

The consortium partners have made substantial progress on all aspects of the project. The key results of this first period are:

• Discovery of chlorine-related spin centres in silicon carbide
A novel family of defects, which result from chlorine implantation, has been identified. Their optical zero-phonon line transitions range from 1.35 µm to 1.56 µm, spanning the telecom domain. They are strong candidates for fast single-photon sources due to their fast optical transitions with sub-ns lifetimes. Their spin properties are under intense scrutiny. Partners LIU and HZDR have provided first reports on their properties in
A.N. Anisimov, A.V. Mathews, K. Mavridou, U. Kentsch, M. Helm, G.V. Astakhov,
“Engineering chlorine-based emitters in silicon carbide for telecom-band quantum technologies,”
Opt. Express 33 (2025) 54285. https://doi.org/10.1364/OE.581705.
A.N. Anisimov, K. Mavridou, A.V. Mathews, M. Helm, G.V. Astakhov,
“Telecom-band quantum memory with chlorine defects in silicon carbide”, (2026). https://doi.org/10.48550/ARXIV.2605.03717.
D. Shafizadeh, M. Ghezellou, V.M. Bobal, L. Vines, J. Ul-Hassan, V. Jokubavicius, N.T. Son, I.G. Ivanov, “Spin-active chlorine-related centers in 4H-SiC with telecom-band emissions,”
(2026). https://doi.org/10.48550/arXiv.2602.08854.

• Creation of spin centres by highly precise, localized implantation
Implantation masks formed by electron beam lithography have been fabricated on bespoke SiC substrates from within the consortium. The masks allow to reach positioning precision on the order of 50 nm, including straggle, which is Implantation through such masks has been performed with both chlorine and vanadium atoms.

• Design and fabrication of a first photonic integrated circuit for photon routing
The consortium partners have designed and created a first prototype waveguide circuit which allows to route the photonic signals to and from twelve sites in the network.

• Assembly of a chip stack containing a SiC membrane doped with vanadium
The stack forms a Fabry-Pérot microcavity with a high-performance concave silicon micromirror and is coupled directly to telecom optical fibers.

• Definition of core benchmarks and their relation to physical properties of the spin centres
The key performance indicators of the envisaged network have been defined, allowing to calculate informed projections for the entanglement rates and enabling focused optimization of the system properties.

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)

The results achieved so far strengthen the position of silicon carbide as a key material in quantum technology, and underline the beneficial aspects of collaboration between industrial technology leaders, nascent enterprises, and fundamental research. Armed with the progress of the first period, it is now possible to pursue the highly ambitious goals of QuSPARC that will deliver the foundation for industrial deployment. Technological development of the envisaged quantum technological systems provides strong support for the silicon carbide platform, with its many applications in (quantum) sensing, power electronics, electromobility, and green energy. The next phase of the project will allow the demonstration of key results which will encourage further uptake of the material platform. Access to additional financing tools is a key need for accelerated progress towards the larger goals within and beyond the scope of QuSPARC.