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Superconductor Science and Technology

Hardware Trojans in superconducting electronic circuits

Ayisat Adedokun, Yerzhan Mustafa, Selçuk Köse

Published Jul 1, 2025• 2 citations
Publisher

Abstract

Abstract Hardware Trojans that exploit the unique characteristics of superconducting electronic (SCE) circuits are explored in this paper. Two types of hardware Trojan circuits are proposed: a magnetically-coupled data transmission Trojan embedded in single flux quantum full adder circuit and a pulse-interleaved Trojan implemented within a frequency divider. The working principles of how these Trojan circuits exploit the frequency-sensitive nature of SCE circuits are explained. The proposed Trojan circuits stay hidden during typical low-frequency testing, and only triggered and become active (and potentially dangerous) at higher frequencies. Extensive analysis demonstrate that these Trojans have a high chance of staying stealthy during testing, underscoring the need for more comprehensive security measures that account for the full range of operating frequencies for the protection of both classical superconducting systems and future quantum technologies.

DOI
10.1088/1361-6668/adeb38

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Abstract Hardware Trojans that exploit the unique characteristics of superconducting electronic (SCE) circuits are explored in this paper. Two types of hardware Trojan circuits are proposed: a magnetically-coupled data transmission Trojan embedded in single flux quantum full adder circuit and a pulse-interleaved Trojan implemented within a frequency divider. The working principles of how these Trojan circuits exploit the frequency-sensitive nature of SCE circuits are explained. The proposed Trojan circuits stay hidden during typical low-frequency testing, and only triggered and become active (and potentially dangerous) at higher frequencies. Extensive analysis demonstrate that these Trojans have a high chance of staying stealthy during testing, underscoring the need for more comprehensive security measures that account for the full range of operating frequencies for the protection of both classical superconducting systems and future quantum technologies.
Abstract Superconducting qubits have emerged as the leading qubit modality for quantum computing. Recent efforts by both academic and industrial researchers aim to enable high-speed, low-noise, and potentially scalable control and measurement of these qubits with superconducting digital electronics. Because the technology is still in an early phase of development, the classical control plane that communicates with quantum systems represents an attack surface that has not yet been thoroughly examined. This work exposes a critical vulnerability by presenting a frequency-activated hardware Trojan—termed as the data transmission Trojan (DT-Trojan)—embedded within a single-flux-quantum (SFQ) digital logic path. The DT-Trojan is functionally indistinguishable from a nominal flip-flop during conventional low-frequency bias-margin testing, but gets triggered at higher frequencies through a magnetically coupled feedback loop that introduces deterministic phase perturbations. Once triggered, the Trojan corrupts high-frequency SFQ pulse streams by disrupting phase coherence, which reduces quantum gate fidelity and leaks information covertly through spectral sidebands. Comprehensive circuit-level simulations using the JoSIM superconducting circuit simulator validate this dual-mode behavior. The results demonstrate a greater than 75% reduction in control fidelity and measurable spectral leakage once activated, underscoring the difficulty of detecting frequency-dependent Trojans in cryogenic environments. This work highlights an emerging class of security threats in SFQ-based quantum control and calls for verification strategies that account for high-frequency switching dynamics and magnetic-coupling effects in superconducting electronics.
Quantum computing has demonstrated superior efficiency compared to classical computing. Quantum circuits are essential for implementing functions and achieving correct computational outcomes. Quantum circuit compilers, which translate high-level quantum operations into hardware-specific gates while optimizing performance, serve as the interface between the quantum software stack and physical quantum machines. However, untrusted compilers can introduce malicious hardware Trojans into quantum circuits, altering their functionality and leading to incorrect results. In the world of classical computing, effective hardware Trojans are a critical threat to integrated circuits. This process often involves stealthily inserting conditional logic gates that activate under specific input conditions. In this paper, we propose a novel advanced quantum Trojan that is controllable, allowing it to be activated or deactivated under different circumstances. These Trojans remain dormant until triggered by predefined input conditions, making detection challenging. Through a series of benchmark experiments, we demonstrate the feasibility of this method by evaluating the effectiveness of embedding controlled trojans in quantum circuits and measuring their impact on circuit performance and security.
Quantum computing has demonstrated superior efficiency compared to classical computing. Quantum circuits are essential for implementing functions and achieving correct computational outcomes. Quantum circuit compilers, which translate high-level quantum operations into hardware-specific gates while optimizing performance, serve as the interface between the quantum software stack and physical quantum machines. However, untrusted compilers can introduce malicious hardware Trojans into quantum circuits, altering their functionality and leading to incorrect results. In the world of classical computing, effective hardware Trojans are a critical threat to integrated circuits. This process often involves stealthily inserting conditional logic gates that activate under specific input conditions. In this paper, we propose a novel advanced quantum Trojan that is controllable, allowing it to be activated or deactivated under different circumstances. These Trojans remain dormant until triggered by predefined input conditions, making detection challenging. Through a series of benchmark experiments, we demonstrate the feasibility of this method by evaluating the effectiveness of embedding controlled trojans in quantum circuits and measuring their impact on circuit performance and security.
Single flux quantum (SFQ) technology is currently used as a cryogenic control and readout circuitry of superconducting quantum computers. The low power operation and high switching frequency of SFQ technology are instrumental to efficiently scale a quantum computer. With the growing interest in the hardware security of SFQ circuits, a novel side-channel leakage mechanism in SFQ-to-dc converters is uncovered in this article. The leakage mechanism is investigated for two logic styles, namely, rapid SFQ (RSFQ) and energy-efficient RSFQ (ERSFQ). By observing the fluctuations in the power supply provided by the room temperature electronics, a malicious adversary can extract critical information about the applied input signals. This type of side-channel leakage can lead to serious security vulnerabilities for superconducting electronics and quantum computers. Two potential side-channel attacks that exploit this vulnerability and target SFQ-based qubit control and readout systems are proposed.
Superconducting devices have intrinsically superior characteristics to those of semiconductor devices. Presently, we can fabricate more than twenty thousand junctions on one chip using niobium technology. We have demonstrated the operation of a network system with a superconducting interconnection chip using voltage-state logic. Single flux quantum devices are promising for future superconducting applications because the clock frequency of SFQ logic is higher than that of voltage-state. We have proposed a high-end switch based on hybrid architecture using optical devices, semiconductors and SFQ devices. To demonstrate the high-speed operation of SFQ circuits, we developed an arbiter circuit that uses SFQ components and the arbiter circuit operates at 60 GHz. We also have developed a high Tc superconducting (HTS) SFQ sampler system for observing ultra-fast signal waveforms. In addition, we will discuss the prospects of future superconducting devices based on the fabrication technologies we developed.
Single flux quantum (SFQ) logic circuits, in which a single flux quantum is used for an information carrier, have a possibility to open a new digital system operated with over 100 GHz clock frequencies at extremely low power dissipations. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits with high speeds has been done. By taking advancements in these designing tools, circuits including more than several thousands junctions easily operated with the clock frequency of more than several tens GHz. Applications of SFQ circuits such as high performance computers, high end router and high end servers are being developed in the world taking advantages of the high through-put nature and the low power dissipation of the SFQ logic.