Compatibility with noisy intermediate-scale quantum (NISQ) devices is crucial for the realistic implementation of quantum cryptographic protocols. We investigate a cryptographic scheme based on discrete-time quantum walks (DTQWs) on cyclic graphs that exploits Parrondo dynamics, wherein periodic evolution emerges from a deterministic sequence of individually chaotic coin operators. We construct an explicit quantum circuit realization tailored to NISQ architectures and analyze its performance through numerical simulations in Qiskit under both ideal and noisy conditions. Protocol performance is quantified using probability distributions, Hellinger fidelity, and total variation distance. To assess security at the circuit level, we model intercept-resend and man-in-the-middle attacks and evaluate the resulting quantum bit error rate. In the absence of adversarial intervention, the protocol enables reliable message recovery, whereas eavesdropping induces characteristic disturbances that disrupt the periodic reconstruction mechanism. We further examine hardware feasibility on contemporary NISQ processors, specifically $ibm\_torino$, incorporating qubit connectivity and state-transfer constraints into the circuit design. Our analysis demonstrates that communication between spatially separated logical modules increases circuit depth via SWAP operations, leading to cumulative noise effects. By exploring hybrid state-transfer strategies, we show that qubit selection and connectivity play a decisive role in determining fidelity and overall protocol performance, highlighting hardware-dependent trade-offs in NISQ implementations.

翻译：与嘈杂中等规模量子（NISQ）设备的兼容性对于量子密码协议的实际实现至关重要。本研究探讨了一种基于循环图上离散时间量子行走（DTQW）的密码方案，该方案利用了帕隆多动力学——即通过确定性序列的个体混沌硬币算符产生周期性演化。我们构建了专门针对NISQ架构的显式量子电路实现，并通过Qiskit在理想和噪声条件下的数值模拟分析了其性能。协议性能采用概率分布、海林格保真度和总变差距离进行量化。为评估电路级安全性，我们建模了拦截-重发和中间人攻击，并评估了由此产生的量子比特错误率。在无对抗干预的情况下，该协议可实现可靠的消息恢复；而窃听行为会引发特征性扰动，破坏周期性重构机制。我们进一步考察了在当代NISQ处理器（特别是$ibm\_torino$）上的硬件可行性，将量子比特连通性和状态传输约束纳入电路设计。分析表明，空间分离的逻辑模块间通信会通过SWAP操作增加电路深度，导致累积噪声效应。通过探索混合状态传输策略，我们证明量子比特选择与连通性对决定保真度及整体协议性能具有决定性作用，凸显了NISQ实现中硬件相关的权衡关系。