What is quantum Internet?
Quantum Internet is the Internet of Quantum Information. It consists of a platform part that shares quantum entanglements between arbitrary nodes and transmits qubits, and an application part that executes quantum Internet algorithms using shared quantum entanglements and transmitted qubits. Typical applications of quantum Internet include extension of quantum computation such as distributed quantum computation and secret quantum computation, extension of quantum sensing such as ultra-high accuracy of astronomical telescopes, and quantum communication algorithms such as quantum key delivery and quantum authentication (with End-to-End security) that do not have to assume the safety of quantum bitcoin reader selection and relay nodes. In this way, quantum technology and quantum information are connected over a wide area.
Two types of quantum networks
In fact, a computer network called the Trusted node quantum cryptography network exists as a pre-stage of the quantum Internet. Trusted node quantum cryptographic network is a network that delivers classical bits (encryption keys). Since each relay node converts cryptographic keys from quantum information to classical information, the relay technology of trusted node quantum cryptographic networks is called "classical relay". On the other hand, the technology to relay quantum signals as quantum signals is called "quantum relay". The signal relaying function is essential for computer networks, and current Internet routers, for example, route and relay signals. Because of the difficulty of realizing quantum relay technology, research and development of quantum Internet has been under fire for a while, and research to compose quantum networks through classical relays has become popular. Recently, however, with the development of quantum computer research, research on the manipulation of qubits and memory functions has made strides. Research on technologies that connect qubits and light has also progressed greatly, and research and development of the quantum Internet is flourishing worldwide.
Initiatives at Mercari
The quantum entanglement of two qubits is called Bell pair in particular. In fact, the basic function of quantum Internet is the sharing of Bell pair between arbitrary nodes. The reason bell pair sharing alone is sufficient is that quantum teleportation can be performed through Bell pair consumption and classical communication. Quantum teleportation is an operation in which when any qubit is entered from a split of Bell pair, the same qubit is output from the opposite split. In this case, Bell pair is consumed. In other words, in order to send and receive quantum information, it is necessary to create the same number of Bell pair between the two end nodes as the qubit that you want to send using the quantum Internet, and perform quantum teleportation.
But questions remain. Why share Bell pair and then perform quantum teleportation instead of sending qubits directly? This is because photons, which are the media that sends qubits, are losed. Quantum communication encodes information in units of photons. When the photon is passed through a communication medium such as an optical fiber, the photon is absorbed by the fiber itself with a certain probability, and quantum information encoded in the photon is also lost. This information loss is a thorny issue because qubits cannot be copied.
Let's consider Bell pair and quantum teleportation. Bell pair is a two-quantum state expressed as (|00>+|11>)/√2, and can be created as many times as you like. Therefore, when you send a piece of Bell pair (photon) created by a node to a neighboring node, you can share the new Bell pair between the end nodes by re-running the sharing process from the beginning, even if the photons are lost in transmission. Then, by consuming shared Bell pair and performing quantum teleportation, you can safely transmit the quantum state you really want to send without jeopardy.
To create Bell pair between any node in the quantum Internet, use entanglement swinging (called E.S.) to "connect" Bell pair. When E.S. shares one set of Bell pair at points A and B, B and C, it consumes these two Bell pair and creates a Bell pair between points A and C. Relay nodes can achieve routing by changing the combination of Bell pair to connect to. This is the quantum router. Mercari is working on architectures and protocols that realize quantum Internet using these basic operations and their applications.
Project Summary
In previous research on quantum Internet, the physical layer has been the center. Now, with an eye to the realization of the quantum Internet, there is a need for a computer networking mechanism for quantum Internet with quantum properties that scales to a global network, such as routing algorithms and resource management methods. This will also lead us to think about future research on the physical layer.
In this project, with the goal of "development of quantum TCP/IP", we are working on quantum networking research with a focus on research on Best effort, which is suitable for quantum Internet. Best effort is an important concept that gives scalability, fault resistance, and persistence to the current Internet, which changes configurations unevenly and dynamically, and works on a global scale. We believe that by properly incorporating Best effort into the quantum Internet, we can make the quantum Internet practical on a global scale. We also propose a higher communication layer implemented on the end node to enable guaranteed end-to-end communication.
The scheme of this project solves complex state management and long-term resource-only problems in the quantum Internet, and contributes to the realization of infrastructure in the coming quantum premise
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