Experimental investigation of practical unforgeable quantum money

Mathieu Bozzio,Iordanis Kerenidis,Eleni Diamanti,Adeline Orieux,Isabelle Zaquine,Luis Trigo Vidarte

doi:10.1038/s41534-018-0058-2

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.

Highlights

The fundamental property of quantum mechanics at the heart of quantum cryptography is the no-cloning theorem,[1] which states that it is physically impossible to clone an unknown quantum system, that is, to generate two identical copies of the system starting from a single copy
Heisenberg’s uncertainty principle ensures that measuring the encoded qubit in one of the two bases destroys any information about the encoding in the other, while the nocloning theorem ensures that only a party knowing the basis used for the encoding can unambiguously recover the encoded information upon measurement of the qubit. This idea was subsequently extensively used in many quantum cryptographic schemes,[3] and in particular in the BB84 quantum key distribution protocol,[4] which has since thrived as one of the most studied and successfully implemented quantum information applications.[5,6]
The bank verifies the authenticity of the credit card using the secret string s and and to implementations with weak coherent states. We demonstrate that these conditions are rigorously satisfied experimentally using a practical photonic setup based on polarization encoding of weak coherent states of light, and we analyze operational regimes where unforgeability is guaranteed

Summary

INTRODUCTION

The fundamental property of quantum mechanics at the heart of quantum cryptography is the no-cloning theorem,[1] which states that it is physically impossible to clone an unknown quantum system, that is, to generate two identical copies of the system starting from a single copy This property in essence prevents a malicious party from recovering information about the system without disturbing it, something that is always possible in the classical world. Our experiment includes the full procedure of credit card state generation, readout and verification and is compatible with the future use of quantum storage devices, paving the way for the realization of quantum money transactions with informationtheoretic security impossible to achieve in the classical world. The main idea here is that a valid credit card can always be verified in the ideal case: the vendor performs a measurement in

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