Backdoor Threats in Variational Quantum Circuits: Taxonomy, Attacks, and Defenses

2026-05-13

AI Summary

This work addresses the critical security vulnerabilities of Variational Quantum Circuits (VQCs), which are widely deployed in the NISQ era yet remain susceptible to backdoor attacks due to their reliance on predefined architectures and pre-trained models, thereby compromising system reliability. The study presents the first systematic taxonomy of backdoor threats against VQCs, encompassing data poisoning, compiler-level, and quantum-native attack vectors. It formalizes a unified threat model by integrating quantum machine learning, classical backdoor analysis, and quantum compilation techniques. Through theoretical modeling and empirical evaluation, the research elucidates the unique characteristics of quantum-specific threats. Beyond reviewing existing attack and defense strategies, it critically identifies the limitations of current defenses in quantum settings, highlights key challenges, and lays the groundwork for developing robust, quantum-aware security mechanisms for hybrid quantum-classical systems.

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.

Problem

• backdoor attacks
• variational quantum circuits
• quantum security
• NISQ computing
• adversarial threats

Innovation

• backdoor attacks
• variational quantum circuits
• quantum-native threats
• threat taxonomy
• quantum security