# Experimental investigation of practical unforgeable quantum money

## TL;DR

This paper reports the first experimental implementation of a practical quantum money protocol that uses classical verification and polarization-encoded light, overcoming previous technological barriers to real-world deployment.

## Contribution

It demonstrates a secure, practical quantum money scheme compatible with current quantum memory technology, bridging the gap between theory and real-world application.

## Key findings

- Successful polarization encoding of weak coherent states
- Security analysis considering practical imperfections
- Operates within regimes compatible with quantum memories

## Abstract

Wiesner's unforgeable quantum money scheme is widely celebrated as the first quantum information application. Based on the no-cloning property of quantum mechanics, this scheme allows for the creation of credit cards used in authenticated transactions offering security guarantees impossible to achieve by classical means. However, despite its central role in quantum cryptography, its experimental implementation has remained elusive because of the lack of quantum memories and of practical verification techniques. Here, we experimentally implement a quantum money protocol relying on classical verification that rigorously satisfies the security condition for unforgeability. Our system exploits polarization encoding of weak coherent states of light and operates under conditions that ensure compatibility with state-of-the-art quantum memories. We derive working regimes for our system using a security analysis taking into account all practical imperfections. Our results constitute a major step towards a real-world realization of this milestone protocol.