Current Trends
Currently, there are two major trends in the field of quantum information and communication research.
Quantum cryptography: One is the development of “quantum cryptography”. It realizes cryptographic protocols that cannot be broken by computing techniques even with advanced computers. Its working principle is based on quantum nature of information carriers. Specifically, quantum key distribution (QKD), which is an basic technology of quantum cryptography, can be realized to some extent by laser light without using a special quantum light sources while skillfully utilizing the quantum nature of light. As a result, technological development and field tests of the QKD networks have progressed rapidly. So, first demonstrations have been performed applying this technology with satellite links. Although there are still challenges such as the need to protect network relay points, QKD is one of the first quantum technologies that approach real markets. In Japan, experimental demonstrations and practical applications are being promoted through industry-academia-government collaboration led by the National Institute of Information and Communications Technology (NICT). Our group is actively involved in this collaboration as well as the process of international standardization and technological development of the QKD network.
Quantum Internet: The other direction is a network that utilizes light carried a correlation specific to quantum mechanics, the so-called quantum entanglement. Just as the current Internet has caused a paradigm shift by connecting not only people but also various things, new possibilities can be achieved on networks with quantum entanglement distributed between nodes equipped with for instance quantum computers or quantum sensors. So, the goal of the research on the quantum Internet (quantum network) is to realize a novel communication technology. Various functions of the QKD network can be expanded here. However, the entanglement is not easy to distribute and preserve on the network because it is easily destroyed for instance by channel loss and noise. Various physical systems and protocols have been proposed to realize “quantum relay” that repairs broken quantum entanglement in the communication path. Also, basic experiments for its realization have been conducted. Nevertheless not all problems have been solved, and both theory and experiments are still bein actively developed.
Background of the Research
Basic ideas of the Quantum Information Theory research can be summarized as follows.
Quantum Information Theory establishes basic principles of communication performance in quantum cryptography and the quantum Internet. By applying the ideas of Shannon information theory with quantum mechanics it allows for finding the limits of various communication and information processing tasks. Shannon’s channel coding theorem is a theory that reveals the ultimate performance limits of error-correcting codes in noisy channels. These limits are important performance indicators when designing concrete codes and communication systems. On the other hand, by reviewing quantum mechanics based on the idea of information theory we can explore basic properties of quantum mechanics. For example, the idea of information theory plays an important role in quantification of the correlation of quantum entanglement.
Examples of Research Topics
In our laboratory, we are engaged in a wide range of research described by such keywords like “quantum information theory”, “quantum control of light-matter interactions”, and “design of quantum network”. We develop basic theory of quantum information and search of physical systems and system designs of various quantum network. Specific topics we are interested in are:
- Research on new quantum relay method (near-term quantum repeater)
- Research on quantum reception technology
- Research on relay and distillation of multi-partite entanglement
- Study of network quantum information theory
In addition to this, I am also involved in the study of quantum network architectures at forums, international standardization of QKD technology and technological development through the industry-academia-government collaboration.
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