Qu Center

Introduction

It remains a central challenge in quantum information science to scale quantum information processing beyond individual devices and to make effective use of the resulting large-scale systems. A core interest of the Center is to address this challenge through theoretical work on quantum networks and distributed quantum computation. We also investigate quantum algorithms and protocols to clarify how computational advantages can be systematically extracted when quantum computation is extended across multiple, interconnected quantum systems. These scaling-oriented studies are complemented by foundational research on quantum control and non-classicality, which underpin all quantum information processing.

Quantum Networks in Scalable Quantum Information Processing

To scale quantum information processing in size and complexity, multiple quantum systems must be integrated so as to function collectively as a larger computational resource, forming a quantum network. The resulting system necessarily reflects the complexity of the intended task. Developing a theory of quantum networks therefore requires appropriate abstractions of such structures, together with deep insight into the capabilities and limitations imposed by networked architectures.

Principles of Distributed Quantum Computation

Formulating general principles of information processing in quantum domains constitutes a fundamental question, particularly in distributed settings, where multipartite systems admit physical descriptions that are irreconcilable with classical ones. Progress in distributed quantum computing depends not only on advances in our understanding of physical constraints but also on the adoption of appropriate conceptual frameworks through which quantum information processing tasks are modeled and understood. These frameworks are not fixed a priori, but must be shaped and refined against concrete information processing tasks.

Operational Characterization of Quantum Resources

We analyze the operational roles of quantum resources, such as entanglement, quantum memory, and quantum and classical communication, in distributed and networked scenarios. Unlike the standard entanglement theory that treats local operations and storage as freely available, our work explicitly accounts for the costs and limitations associated with memory, communication, and coordination across separated systems. The goal is to determine which resources are critical to implement quantum operations across distributed systems, how different resources can be transformed or combined, and how their availability constrains achievable tasks.

Network-Aware Quantum Algorithms and Protocols

We study quantum algorithms and protocols that are explicitly designed for distributed configurations, where computation and communication are intertwined. Rather than assuming monolithic processors, this topic considers how quantum tasks can be structured across multiple nodes and how non-local operations can be coordinated. The impact on algorithmic performance is inspected with respect to the availability and distribution of quantum resources. All in all, these contribute to the identification of general principles that govern the effective use of large-scale, networked quantum systems.

System-Level Evaluation of Quantum Network Components

This research constructs theoretical frameworks for assessing the performance of quantum nodes when they operate as components of a larger quantum network. We propose figures of merit that are tailored for distributed quantum settings, along with associated quantum algorithms, to enable efficient characterization of individual devices' functionality and to facilitate real-time monitoring and operation of large-scale quantum networks.

High-Fidelity Modeling and Simulation of Quantum Systems

We build theory-driven modeling and simulation programs that aim to capture the microscopic dynamics of quantum devices interacting with quantum fields in network-relevant conditions. A key concern is achieving sufficient accuracy to faithfully represent error mechanisms, correlations, and dynamical effects, crucial to large-scale and fault-tolerant quantum information processing. We devise computational methods for simulating high-dimensional quantum systems, balancing overall tractability with the level of precision required for reliable device modeling and system-level analysis.

Quantum Control and Manipulation

Controlling quantum systems with precision is indispensable to unlocking their full potential. We focus on quantum control tasks to uncover the principles that govern quantum information processing. However, real-world implementations are inevitably affected by control errors and environmental decoherence. We examine how these imperfections influence our ability to manipulate quantum systems and their mitigation methods. Through these efforts, we seek to establish more effective control strategies, paving the way for more powerful and robust quantum information processing.

Non-Classicality in Quantum Systems

Quantum mechanics reveals phenomena that violate classical intuition, showcasing the unique nature of quantum systems. We explore such non-classicality and its consequences in the manipulation of quantum states to uncover new ways to harness quantum mechanics for information processing that transcends classical limitations.

RESEARCH

NII

japan