Curator's Take
This comprehensive survey tackles a critical blind spot in quantum computing security by systematically cataloging how malicious actors could embed hidden "backdoors" in variational quantum circuits—the workhorse algorithms expected to power near-term quantum applications. As quantum machine learning and optimization move toward practical deployment, these findings reveal that the same pretraining and circuit reuse practices that make VQAs efficient also create unprecedented attack vectors that traditional cybersecurity defenses aren't equipped to handle. The research is particularly timely given the growing interest in quantum cloud services and collaborative quantum algorithm development, where users might unknowingly deploy compromised circuits. By formalizing threat models specific to quantum systems, this work provides the foundation for developing quantum-aware security protocols before these vulnerabilities can be exploited in real-world quantum applications.
— Mark Eatherly
Summary
Variational quantum algorithms (VQAs) are a central paradigm for noisy intermediate-scale (NISQ) quantum computing, yet their reliance on predesigned and pretrained variational quantum circuits (VQCs) introduces critical security vulnerabilities, particularly backdoor attacks. These attacks embed hidden malicious behaviors that remain dormant under normal conditions but are activated by specific triggers, leading to adversarial outcomes such as incorrect predictions or manipulated objective values. This paper presents a survey of backdoor attacks in VQCs, covering data-poisoning, compiler-level, and quantum-native mechanisms. We formalize key terminology and threat models, and review existing attack strategies along with their empirical characteristics. We also analyze current detection and defense approaches, highlighting their limitations, especially against quantum-specific threats. By synthesizing recent advances, this survey outlines the evolving security landscape of VQCs and identifies key challenges and future directions for developing robust, quantum-aware defenses in hybrid quantum-classical systems.