Security of quantum computing

Abstract

This thesis investigates crosstalk in superconducting quantum computers—an issue that threatens both the scalability and security of future quantum systems. Crosstalk arises from unintended qubit interactions and compromises the confidentiality, integrity, and availability of quantum computations. The study reviews recent research on crosstalk-based attacks and evaluates a range of mitigation strategies, including hardware-level methods like buffer qubits and dynamic decoupling, and software-based solutions such as crosstalk-aware scheduling and randomized compilation.

To assess crosstalk’s impact, six experiments were conducted using real quantum hardware. The experiments ranged from assessing the impact of malicious CNOT queues on the Bernstein-Vazirani algorithm to exploring the time evolution of quantum states with and without neighboring gate activity. The experimental setups tested variables such as spatial proximity, circuit complexity, and gate types to isolate and understand the influence of crosstalk. Results show that crosstalk decreases with distance between circuits but can produce complex, nonlinear effects. Surprisingly, active gate sequences sometimes led to better performance than idle ones.

The findings emphasize that crosstalk is a multifaceted challenge requiring more study, especially in longer circuits and alternative quantum platforms. No single mitigation approach is sufficient, and future efforts should focus on developing scalable, technology-agnostic strategies.