Experimental practical quantum tokens with transaction time advantage

TL;DR

This paper demonstrates the first practical implementation of quantum S-tokens that offer secure, private, and instant transactions with a measurable time advantage over classical methods, even with experimental imperfections.

Contribution

It presents the first experimental demonstration of secure quantum S-tokens that achieve a transaction time advantage over classical schemes in real-world optical fiber networks.

Findings

Achieved a 88.24% efficiency heralded single-photon source.

Demonstrated a transaction time advantage of 2.77 km and 60.54 km optical fiber networks.

Proved security despite errors, losses, and imperfections.

Abstract

Quantum money is the first invention in quantum information science, promising advantages over classical money by simultaneously achieving unforgeability, user privacy, and instant validation. However, standard quantum money relies on quantum memories and long-distance quantum communication, which are technologically extremely challenging. Quantum "S-money" tokens eliminate these technological requirements while preserving unforgeability, user privacy, and instant validation. Here, we report the first full experimental demonstration of quantum S-tokens, proven secure despite errors, losses and experimental imperfections. The heralded single-photon source with a high system efficiency of 88.24% protects against arbitrary multi-photon attacks arising from losses in the quantum token generation. Following short-range quantum communication, the token is stored, transacted, and verified using classical bits. We demonstrate a transaction time advantage over intra-city 2.77 km and inter-city 60.54 km optical fibre networks, compared with optimal classical cross-checking schemes. Our implementation demonstrates the practicality of quantum S-tokens for applications requiring high security, privacy and minimal transaction times, like financial trading and network control. It is also the first demonstration of a quantitative quantum time advantage in relativistic cryptography, showing the enhanced cryptographic power of simultaneously considering quantum and relativistic physics.