Backdoor Threats in Variational Quantum Circuits: Taxonomy, Attacks, and Defenses
2026-05-13 • Cryptography and Security
Cryptography and Security
AI summaryⓘ
The authors explain that variational quantum algorithms, which are important for current quantum computers, can have hidden security problems called backdoor attacks. These attacks hide harmful behaviors that only activate when triggered, causing wrong results or tampering. The paper reviews different types of backdoor threats and how they work at the data, software, and quantum levels. It also looks at current ways to detect and defend against these issues but notes that many defenses are not fully effective for quantum-specific risks. Overall, the authors highlight the need for better security measures tailored to quantum-classical systems.
Variational Quantum AlgorithmsNoisy Intermediate-Scale Quantum (NISQ)Variational Quantum CircuitsBackdoor AttacksData PoisoningQuantum CompilerQuantum-native ThreatsQuantum-classical Hybrid SystemsSecurity VulnerabilitiesAdversarial Attacks
Authors
Lei Jiang, Fan Chen
Abstract
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.