European Software Stack for Hybrid Quantum Computing

Quantum computers promise new solutions for complex problems in science and industry. To harness this potential in practice, they must work efficiently alongside classical high-performance computers (HPC). To achieve this, the EU-funded project EuroQSS is developing an open, interoperable quantum software stack (QSS) that integrates existing European approaches and simplifies access to hybrid quantum-classical applications. EuroQSS brings together 13 project partners from seven European countries.

The European quantum software landscape has so far been fragmented: Many software stacks are tailored to specific hardware platforms, are only partially integrated into HPC infrastructures, and are not yet prepared for fault-tolerant quantum computing (FTQC). As a result, researchers and companies must familiarize themselves with different systems and make numerous technical decisions that could often be handled automatically. EuroQSS aims to reduce these hurdles through common interfaces, end-to-end hybrid workflows, and appropriate abstraction layers.

EuroQSS brings together several existing European approaches into a universal, modular architecture with open interfaces. The project supports end-to-end hybrid quantum-classical workflows and provides the necessary abstraction so that companies, researchers, and software developers can use quantum technologies without having to deal with the details of individual hardware platforms. Programming remains largely hardware-independent. Open interfaces at all levels enable the easy integration of existing and future components, whether open source or commercial. This creates a flexible European quantum ecosystem that brings together different technologies and can continue to evolve over time.

To ensure that hybrid quantum-classical applications can be executed reliably, EuroQSS coordinates the classical and quantum-based computational steps within a shared infrastructure. A benchmarking pipeline based on QUARK measures criteria such as runtime, accuracy, and resource utilization. The results are fed into a central benchmarking database. Building on these results, an AI-powered recommendation system, extending the existing QuaST Decision Tree, helps users identify the most suitable quantum processors, compilers, and execution strategies. In this way, EuroQSS combines hardware-independent programming with hardware-specific optimization, creating a foundation that supports both today’s NISQ (“Noise Intermediate-Scale Quantum”) systems and future fault-tolerant quantum computers.

With the targeted technology maturity level 6 (“prototype in operational environment”), EuroQSS creates a software stack usable throughout Europe for research, software development, and industrial testing in quantum computing. Researchers benefit from reproducible experiments and comparable benchmarks. Companies can use hybrid quantum applications with less customization effort, better evaluate technical options, and reduce their dependence on individual vendors.

A key focus of EuroQSS is delivering solutions that meet real industrial needs. For this reason, the project partners are testing the quantum software stack in five use cases:

• Simulations of chemistry and materials
• Fluid dynamics in aerospace
• Quantum-enhanced AI
• Industrial optimization
• AI-assisted hardware characterization

All reference applications combine quantum and HPC components, are scalable from NISQ to FTQC, and are evaluated using common metrics.

With training materials for industrial users and software developers, the project partners also ensure rapid knowledge transfer and gather timely feedback from potential industrial users.

By the end of the project in 2029, EuroQSS will provide an open, interoperable, and Europe-wide quantum software stack.

The following will be possible by the end of the project:

1. Hybrid quantum-classical applications can be implemented more easily. This is central to the use of quantum computing, as it will always take place in collaboration with classical computers. The quantum advantage lies in these hybrid applications.
2. Developers and users will be able to utilize quantum hardware more efficiently, even without expert knowledge of technical details.
3. Different quantum platforms can be integrated via common interfaces. EuroQSS enables hardware-independent programming while simultaneously allowing for hardware-specific optimization.
4. The benchmarking and evaluation methods developed allow for the reproducible assessment of the performance of the new solutions.
5. European companies gain easier access to quantum computing technologies.

In this way, the EU project EuroQSS bridges the gap between quantum hardware and industrial applications, making quantum computing practically usable.

The European consortium and the connection to existing initiatives also strengthen an open quantum ecosystem and Europe’s technological sovereignty.

This project is funded by the European Union under @HorizonEU research and innovation program.

Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the granting authority can be held responsible for them.