Japanese Companies Demo Unforgeable Quantum Tokens

In November, the technology took a step forward when Mitsui, NEC and Quantinuum collaborated declare They used off-the-shelf equipment to successfully deliver and redeem quantum tokens through Tokyo’s 10-kilometer optical fiber network, which was the first time in the industry. Quantum tokens are delivered using a new exchange protocol that uses a technology called Quantum key distribution (QKD).

QKD is theoretically unbreakable

In theory at least, QKD is an unbreakable method of sharing a key between two parties, which can then be used to encrypt and decrypt private messages. The technology is currently being tested by financial institutions, government entities, major technology companies and the military.

QKD exploits the quantum properties of photons, specifically measuring properties such as polarization that change their quantum state. Photons used in QKD are usually generated by specialized hardware, e.g. laser. By using polarizing filters, QKD transmits these photons between the two parties as a randomly selected sequence of single photons, with each photon representing a bit, said Jefferson Florez, senior photonics engineer at Quantinuum.

Only a subset of photons is selected to form the key, and each bit can only be read accurately using the correct filter. A third party cannot determine which filters are used, so a data thief cannot copy a photon bit without changing its state and warning the user in the process. The basis of this security plan is No cloning theoremwhich states that it is impossible to copy unknown and arbitrary quantum states.

Duncan Jones, head of the Quantinuum network, which owns the intellectual property rights behind the quantum token protocol, described the use cases of quantum tokens, using banks and customers as examples. After receiving Quantum Tokens from the bank, in order to redeem their value at the branch of his choice, the customer needs to send a message to the bank using standard methods. The encrypted message included the name of the branch and his digital token data, to which he added a random bit so that the bank could not read the communication, but could still identify and verify it. The bank then sends a copy of the communication to all its branches.

“When a customer submits their token data to a designated branch, that data is verified locally without the need for cross-checking,” Jones said. “The token can only be used once and cannot be redeemed at other branches.”

The quantum key distribution test involves two QKD units representing the bank and the customer, and allows customers to redeem quantum tokens at a bank branch of their choice for financial transactions.How many

Another use case involves commodity-backed quantum tokens, where the tokens represent tangible assets, such as precious metals. Since quantum tokens are unforgeable, it is impossible to double-spend them. This provides assurance of a central authority for issuance and provides users with the benefits of private, fast transactions and local verification.

“There is currently no known non-quantum solution that provides unforgeability, local verification and privacy at the same time,” Jones said. “Different methods can achieve any two of the three, but you can’t achieve all three at the same time. That’s what’s special about quantum tokens.

The idea of ​​using quantum tokens to represent money dates back to the 1970s Stephanie WeinerProfessor of Quantum Information at Delft University of Technology in the Netherlands. “Through this experiment in Japan, researchers claim that they can exploit arbitrary quantum states that can be used to create tokens that represent money and are essentially impossible to replicate,” she said. But in the absence of any detailed technical documentation, “it is difficult to comment on the veracity of these claims,” ​​she added. “If proven, this use case using existing hardware is very important for implementation.”

Practical testing of unforgeable tokens

While Quantinuum provided the quantum token protocol for the November trial, NEC set up the platform to test the technology. This setup consists of two modified QKD units, one representing the bank and the other representing the customer. Each unit contains a photonic transceiver and a digital processing unit, which are connected by 10 kilometers of dedicated optical fiber. Each digital processor is coupled to an application server, which in turn is connected to an Ethernet-based internal network. This intranet connects the bank and customers to each other and to two computers representing the bank branches.

Based on the quantum token protocol, the bank’s QKD photon transceiver transmits a sequence of random quantum photons to the customer’s transceiver, where it is used to create quantum tokens. The token is converted into digital data and then randomly sent back to the bank along with specified branch information, which forwards the information to the branch. Only designated branches accept token exchange.

Standard quantum key transactions are typically transmitted by QKD devices at hundreds of kilobits per second. But the protocol for quantum tokens is much more complex and requires speeds of around 1 gigabyte per second to make transactions feasible, said Naoto Ishii, director of NEC’s Quantum Cryptosystems Research Group. Engineers also had to modify the QKD device to accommodate the protocol, which proved to be a challenge, he said.

Mitsui & Co. plays the role of project manager in the trial. “We are developing business in the digital transaction space,” said Koji Naniwada, deputy general manager of Mitsui & Co. “So the security and immediacy of quantum tokens are attractive to us.”

Looking ahead, Ishii’s team is working to extend the length of optical fiber that can transmit quantum tokens, possibly to 50 kilometers before quantum data becomes unstable. Other goals include speeding up the transmission and reception of tokens and developing QKD devices that do not require dedicated optical fibers for quantum channels.

In addition to financial applications, NEC believes quantum tokens are also used by large companies and government agencies for encrypted communications. Therefore, as a business, NEC is considering providing technology platforms and quantum token application services.

“While some customization of the platform is required to accommodate applications, we believe the technology is now largely complete and ready for commercial use,” Ishii said.