Multi-Channel Currency: A Secure Method Using Semi-Quantum Tokens
Yichi Zhang, Siyuan Jin, Yuhan Huang, Qiming Shao
TL;DR
This work tackles offline, multi-channel digital payments and the risk of double-spending by introducing a quantum-money inspired protocol based on semi-quantum tokens. The approach combines unclonable quantum token units with certificated destruction, verified via public oracles and augmented by blockchain-enabled transfers, enabling face-to-face, remote no-middleman, and on-chain channels. Experimental validation uses a quantum cloud platform for token minting/signing and a Sepolia Ethereum testnet for smart-contract-based transfers, employing a 4-qubit token representation and denoting token units as $\ket{\$}$. The results demonstrate secure, multi-channel offline transactions with decentralized verification, highlighting practical potential for quantum-secure digital currencies and hybrid quantum-classical financial infrastructures that support financial inclusion.
Abstract
Digital currencies primarily operate online, but there is growing interest in enabling offline transactions to improve digital inclusion. Existing offline methods struggle with double-spending risks, often limiting transaction amounts. In this work, we propose a quantum-state-based currency system that uses the non-cloning theorem to enable secure, multi-channel transactions without the risk of double spending. We demonstrate this system's implementation with experimental results, including use cases for currency transfers and swaps. To mitigate credit risks in swaps, we also integrate blockchain to show its wide applicability. Our approach paves the way for quantum-secure digital currencies and opens new possibilities for optimizing multi-channel tokens.