Secure Quantum Token Processing with Color Centers in Diamond

Abstract: We present a quantum token scheme in which the token is a quantum state that ensures secure authentication or payment. In our approach, rooted in Wiesner's quantum money concept, a token is encoded in a multi-qubit state generated by a single-photon source and transmitted to a user who holds a quantum memory register. By leveraging state-dependent reflection from a highly efficient sawfish nanophotonic crystal cavity and implementing high-fidelity fractional quantum gates through a pulse train of optical $\pi$/8 pulses, our design achieves gate fidelities exceeding 99% under realistic operating conditions. We also analyze microwave control, which extends the viability to longer storage times, albeit at reduced operational rates. We rigorously examine the impact of finite photon bandwidth, cavity design parameters, spectral diffusion, and control imperfections on overall performance. Our comprehensive model indicates that, with near-term improvements in device efficiency and conversion rates, the token acceptance rate can approach the MHz regime for short-distance communication links while remaining robust against optimal cloning attacks. These findings pave the way for integrating unforgeable quantum tokens into larger-scale quantum networks, thereby significantly enhancing the security of future quantum network applications.