Quantum Information Processing with Interacting Parties

Project Information

QInteract

Grant agreement ID: 101078107

DOI

10.3030/101078107

EC signature date 9 December 2022

Start date 1 January 2023

End date 31 December 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 500 000,00

EU contribution

€ 1 500 000,00

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 1 - QInteract (Quantum Information Processing with Interacting Parties)

Reporting period: 2023-01-01 to 2025-06-30

Summary of the context and overall objectives of the project

We are entering an era where quantum hardware capabilities are beginning to meet the requirements of theoretical quantum protocols. This development brings new urgency to a fundamental question in quantum information processing theory: for which tasks do quantum information processing devices outperform their conventional counterparts?

This project addresses the above challenge in the context of information processing with interacting parties, a natural framework for cryptography, communication, and distributed computing. We take a two-pronged approach, with each prong tackling a fundamental aspect of interactive information processing while maintaining a shared focus on efficiency. We focus on two key areas: entanglement-enabled information processing and efficiency in quantum computations.

The first objective explores entanglement, a uniquely quantum phenomenon that enables powerful advantages in multi-party information processing. We aim to deepen the theoretical foundation of entanglement-enabled computations by developing methods to analyze them, identifying practical scenarios where entanglement can be efficiently utilized, and comparing different models of entanglement to understand their computational potential.

The second objective focuses on improving efficiency in quantum computations, particularly for problems with symmetric quantum inputs, which frequently appear in quantum information theory. While much of quantum theory studies the ultimate capabilities of quantum systems, we aim to make these processes more efficient. Specifically, we will develop optimized algorithms for the quantum Schur transform, a widely used quantum tool. Our approach includes creating a streaming implementation of Schur sampling that can run on small-scale quantum devices, designing error-mitigation techniques for real-world quantum hardware, and constructing efficient quantum circuits for port-based teleportation and related applications.

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

Understanding Complexity of Interactive Quantum Information Processing with Entanglement.
Our research has advanced the study of problem complexity in distributed quantum settings. We have developed a key reduction technique, showing that a class of quantum games (quantum independence games) are as complex as the hardest problems in a well-known quantum complexity class. Additionally, we created a 0.864-approximation algorithm for a noncommutative version of the 3-Coloring problem, a major step in extending approximation techniques to quantum systems.

Another breakthrough is a new entanglement-assisted protocol for verifying quantum measurement devices. This provides a powerful method for ensuring that quantum systems function as expected, a crucial need for cryptographic applications. Our team also made important contributions to communication complexity, setting precise bounds on the amount of communication required for distributed agents to solve key graph and Boolean function problems.

Developing Efficient Quantum Algorithms.
We introduced a novel, memory-efficient streaming algorithm for a variant of the quantum Schur transform, a fundamental tool in quantum computing. This enables significant memory savings and makes quantum learning tasks feasible on much smaller devices. Our work also shows that quantum advantage can persist under certain noise conditions, challenging previous assumptions about the impact of errors in quantum computations.

Finally, we applied our streaming algorithm to quantum state tomography, developing a new method that remains sample-optimal while significantly improving memory efficiency. This breakthrough makes state reconstruction more practical for near-term quantum devices, addressing key scalability challenges.

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 of this research have significant potential impacts across multiple areas of quantum computing and information science:

- Stronger Quantum Verification: The entanglement-assisted protocol for certifying quantum measurement devices enhances security and reliability in cryptographic applications, paving the way for more trustworthy quantum technologies.

- Advancements in Quantum Complexity Theory: By extending classical complexity concepts to quantum systems, our work deepens the understanding of problem hardness in quantum computing and provides new tools for solving complex quantum constraint satisfaction problems.

- Improved Efficiency for Quantum Algorithms: The development of a memory-efficient streaming algorithm for the Schur transform enables quantum learning tasks on smaller, near-term devices, making quantum computing more practical and scalable.

- Better Noise Management in Quantum Computation: Our findings on quantum advantage persistence under noise suggest new ways to mitigate errors, which is crucial for building reliable and fault-tolerant quantum systems.

- Enhanced Quantum State Tomography: The improved tomography method reduces memory requirements, making state reconstruction feasible on limited quantum hardware, a critical step toward real-world quantum applications.

Overall, these contributions help bridge the gap between theoretical advancements and practical quantum computing, accelerating progress toward scalable and efficient quantum technologies.