Quantum communication
What is quantum communication?
Quantum communication uses the properties of quantum mechanics to transmit information securely and establish quantum connections between distant systems. Photons are the main carriers of information, allowing the properties of quantum states and entanglement to be used in communication.
Two main areas are quantum cryptography, which is concerned with secure communication, and quantum networks, which connect distant quantum systems. Both draw on quantum information theory to understand the limits of communication performance and security.
Transmitting information securely
Quantum key distribution (QKD) is a representative technology in quantum cryptography. It allows users to share cryptographic keys while detecting eavesdropping, using properties such as the way measurements affect quantum signals. Its security can be guaranteed through the principles of quantum mechanics, without relying solely on the limits of computing power.
Some QKD schemes can be implemented with laser light, without specialized quantum light sources. Work is also progressing on demonstrations over real optical-fiber networks, network integration, and standardization. Takeoka Lab contributes to QKD network technology and standardization in collaboration with research institutes including the National Institute of Information and Communications Technology (NICT).
Connecting distant quantum systems
Another main area is quantum networks that use entanglement to connect quantum computers, quantum sensors, and other devices. This research also contributes to the quantum internet, in which multiple quantum devices are connected at the quantum level to enable new information and communication technologies.
Entanglement is sensitive to loss and noise in communication channels, which makes direct distribution over long distances difficult. Researchers therefore study quantum repeaters, which extend the range by connecting entanglement along the route, and communication protocols that tolerate loss. Quantum networks also have applications beyond communication, including quantum sensing in which measurements are coordinated across distant locations.
Understanding communication limits with quantum information theory
Quantum cryptography and quantum networks raise fundamental questions about how securely information can be transmitted and how much can be sent. Quantum information theory studies these limits mathematically.
In classical communication, Shannon's information theory describes how accurately information can be transmitted through noisy channels. Quantum information theory combines this approach with quantum mechanics to study the performance and security of quantum channels and the properties of entanglement. The resulting limits guide the design of communication schemes and networks, and also offer insights into quantum mechanics itself.
Quantum communication research at Takeoka Lab
We study quantum communication through both theory and experiments, from quantum information theory and network design to optical proof-of-principle demonstrations. We work on basic theory, new communication protocols, and quantum-network system design, alongside experiments with entangled-photon sources, optical fiber, and single-photon detectors.
See the Quantum Communication Theory and Quantum Communication Experiment team pages for research topics and members.
Quantum Communication Theory
We theoretically study the security and performance of communication schemes and the structure of quantum networks, including quantum key distribution, quantum repeaters, and quantum network sensing.
Quantum Communication Experiment
We use photons and optical fiber in experiments on generating, transmitting, and connecting entanglement. We also develop technologies that allow quantum communication and existing optical communication to share the same network.