Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

ACS Applied Materials & Interfaces

Surface Passivation of Niobium Superconducting Quantum Circuits Using Self-Assembled Monolayers

Mohammed Alghadeer, Archan Banerjee, Ahmed Hajr, Hussein Hussein, Hossein Fariborzi, Saleem G. Rao

Published Dec 27, 2022• 18 citations
Publisher

Abstract

Superconducting coplanar waveguide (CPW) microwave resonators in quantum circuits are the best components for reading and changing the state of artificial atoms because of their excellent coupling to quantum systems. This coupling forms the basis of the developing circuit quantum electrodynamic architecture. In quantum processors, oscillators are used to store and transmit quantum information using microwave-frequency wave packets. However, the presence of amorphous thin-film defects is deleterious and can result in an irrevocable loss of coherent information with uncontrolled degrees of freedom. Although there has been extensive research into techniques to reduce the coherent loss of such devices, the precise structure of amorphous dielectric layers on surfaces and interfaces and their associated loss mechanism are being actively studied. In particular, planar superconducting resonators are very sensitive to defects on their surfaces, such as two-level systems in oxidized metals and nonequilibrium quasiparticles, making these devices suitable probes for the different loss mechanisms. In this work, we present the design, fabrication, and characterization of Nb CPW resonators with different surface treatments with self-assembled monolayers (SAMs), which mitigate the growth of oxides in superconducting circuits. We demonstrate SAM-passivated resonators having internal quality factors of greater than 10 6 at a single-photon excitation power (measured at 100 mK), which were probed using scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy to demonstrate the efficiency of our surface treatment. Finally, we compared the improvements in the experimental quality factors to those obtained by numerical simulation.

DOI
10.1021/acsami.2c15667

Related papers

Mitigating coherent loss in superconducting circuits using molecular self-assembled monolayers

Mohammed Alghadeer, Archan Banerjee, Kyunghoon Lee +3 more

In planar superconducting circuits, decoherence due to materials imperfections, especially two-level-system (TLS) defects at different interfaces, is a primary hurdle for advancing quantum computing and sensing applications. Traditional methods for mitigating TLS loss, such as etching oxide layers at metal and substrate interfaces, have proven to be inadequate due to the persistent challenge of oxide regrowth. In this work, we introduce a novel approach that employs molecular self-assembled monolayers (SAMs) to chemically bind at different interfaces of superconducting circuits. This technique is specifically tested here on coplanar waveguide (CPW) resonators, in which this method not only impedes oxide regrowth after surface etching but can also tailors the dielectric properties at different resonators interfaces. The deployment of SAMs results in a consistent improvement in the measured quality factors across multiple resonators, surpassing those with only oxide-etched resonators. The efficiency of our approach i3s supported by microwave measurements of multiple devices conducted at millikelvin temperatures and correlated with detailed X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) characterizations of SAM-passivated resonators. The compatibility of SAMs materials with the established fabrication techniques offers a promising route to improve the performance of superconducting quantum devices.

Scientific Reports•Nov 9, 2024•11 citations

The role of self-assembled monolayers at substrate–metal interfaces in limiting coherence of superconducting quantum circuits

Saleem G. Rao

In planar superconducting quantum circuits, two-level system (TLS) defects within amorphous dielectrics at various circuit interfaces, including substrate–metal (SM) and air-interfaces, are a critical source of decoherence. We employed molecular self-assembled monolayer (SAM) at different interfaces to mitigate TLS losses in superconducting coplanar waveguide (CPW) resonators. Previous work has reported an increase in the resonator quality factor when a SAM is applied to air-interfaces, but a contrasting decrease is observed when the SAM is applied to the metal–substrate interfaces. To investigate the reason behind this decrease, we fabricated and characterized niobium (Nb)-based CPW resonator chips on silicon substrates, both with and without a SAM at the SM interface. Quality factor measurements performed at 100 mK across a wide range of driving powers confirmed that the presence of the SAM at the SM interface led to a reduction in the quality factor. This observed decrease is attributed to an increased TLS defect density, as suggested by the topography of niobium deposited on the SAM. Our findings demonstrate that the roughness of the deposited Nb at the SM interface, which is influenced by the SAM, significantly impacts the density of TLS defects at this interface. Furthermore, simulations of TLS losses in CPW resonators supported our experimental observations by evaluating resonator quality factors under various interface modifications, particularly showing a decrease in the quality factor when the SM interface exhibited high loss.

AVS Quantum Science•Dec 1, 2025•2 citations

Enhanced Tantalum Superconducting Resonator Performance via All-Surface Organic Monolayer Passivation

Harsh Gupta, Moritz Singer, Benedikt Schoof +4 more

Tantalum is a promising platform for superconducting quantum circuits, yet coherence times remain limited by dielectric losses from interfacial two-level systems (TLS), exacerbated by native oxide regrowth. Here, we implement molecular surface passivation using self-assembled organic monolayers on freshly etched tantalum and silicon in coplanar waveguide resonators. Surface characterization by contact angle, XPS, FTIR and TEM confirm the formation of ordered, nanometer-thick films that suppress oxide formation. Microwave measurements in the ~5-9 GHz range reveal internal quality factors up to 1.8x10^6 in the single-photon regime at 100 mK, representing a ~140% improvement over untreated devices with native oxide. Power and temperature dependent measurements attribute this enhancement to reduced TLS-induced losses. These results demonstrate that molecular passivation effectively engineers low-loss interfaces and provides a scalable route toward high-coherence superconducting quantum devices.

cond-mat.mtrl-sciCross-listedarXiv:2604.22112•Advanced Functional Materials•Apr 27, 2026•0 citations

Tantalum-Encapsulated Niobium Superconducting Resonators: High Internal Quality Factor and Improved Temporal Stability via Surface Passivation

Anas Alkhazaleh, Juan Villegas, Florent Ravaux +1 more

Superconducting coplanar waveguide resonators are essential components in quantum processors, where their internal quality factor (Qi) constrains qubit coherence and readout fidelity. In niobium devices, microwave losses at millikelvin temperatures are strongly influenced by two-level systems (TLS) associated with the complex NbOx surface oxide. To mitigate these losses, we investigate a surface-engineering approach in which Nb films are capped in situ with a thin tantalum layer to suppress Nb2O5 formation and replace the native NbOx interface with a Ta-based oxide. We fabricate Nb/Ta bilayer and reference Nb resonators on high-resistivity silicon using identical DC sputtering and wet etching conditions, and characterize their performance at millikelvin temperatures. Fresh Ta-encapsulated devices exhibit internal quality factors up to 2.4 x 10^6 in the near-single-photon regime, with power dependence consistent with reduced TLS-related loss at the metal-air interface. A control Nb device fabricated under the same process shows comparatively lower Q_TLS, consistent with the beneficial effect of the Ta capping layer. Furthermore, ageing tests performed on Nb/Ta resonators after six months reveal a moderate reduction in Q_TLS relative to their initial values, yet the performance remains superior to newly fabricated Nb-only devices. These results suggest that thin Ta encapsulation enhances interface quality and contributes to improved temporal stability while remaining compatible with Nb-based fabrication workflows.

quant-pharXiv:2604.09050•Apr 13, 2026•0 citations

High temporal stability of niobium superconducting resonators by surface passivation with organophosphonate self-assembled monolayers

Harsh Gupta, Rui N. Pereira, Leon Koch +6 more

Abstract One main limiting factor towards achieving high coherence times in superconducting circuits is two-level system (TLS) losses. Mitigating such losses requires controlling the formation of native oxides at the metal-air interface. Here, we report the growth of alkyl-phosphonate self-assembled monolayers (SAMs) on Nb thin films following oxide removal. The impact of passivation was evaluated via the performance of coplanar waveguide resonators at 10 mK, in terms of quality factor and resonant frequency, over six days of air exposure. Un-passivated resonators exhibited an ~80% increase in loss at single-photon power levels, whereas SAM-passivated resonators maintained excellent temporal stability, attributed to suppressed oxide regrowth. By employing a two-component TLS model, we discern distinct prominent loss channels for each resonator type and quantified the characteristic TLS loss of the SAMs to be ~5×10 -7 . We anticipate our passivation methodology to offer a promising route toward industrial-scale qubit fabrication, particularly where long-term device stability is critical.

arXiv:2508.15957•Communications Materials•Jan 12, 2026•2 citations

Mitigation of oxide growth on aluminum thin films: The role of self-assembled monolayers in superconducting quantum circuits

Omar A. Saleh, Saleem G. Rao, Khan Alam +1 more

The native oxide layer formed on aluminum (Al) surfaces in superconducting quantum circuits is a significant source of two-level system defects, which couple with electric fields and degrade quantum coherence. Recent research has explored etching, encapsulation, and other surface treatments as potential strategies to mitigate the formation of oxides at air interfaces in these circuits. This study demonstrates a novel approach to passivate the Al–air interface using a molecular self-assembled monolayer (SAM). Freshly prepared Al thin films were passivated with SAMs by immersing the Al-coated silicon substrates in SAM solutions. X-ray photoelectron spectroscopy (XPS) confirms the successful binding of the SAM and the absence of further aluminum oxide growth. Moreover, the passivation remains stable after aging for 15 days in ambient conditions, as evidenced by XPS and contact angle measurements. Scanning electron microscopy analyses further support the binding of the SAM to the Al surface and mitigation of oxide growth. These findings suggest that SAM-based passivation offers a promising method for reducing microwave loss and improving the performance of Al-based superconducting quantum circuits.

AVS Quantum Science•May 14, 2025•3 citations
Superconducting coplanar waveguide (CPW) microwave resonators in quantum circuits are the best components for reading and changing the state of artificial atoms because of their excellent coupling to quantum systems. This coupling forms the basis of the developing circuit quantum electrodynamic architecture. In quantum processors, oscillators are used to store and transmit quantum information using microwave-frequency wave packets. However, the presence of amorphous thin-film defects is deleterious and can result in an irrevocable loss of coherent information with uncontrolled degrees of freedom. Although there has been extensive research into techniques to reduce the coherent loss of such devices, the precise structure of amorphous dielectric layers on surfaces and interfaces and their associated loss mechanism are being actively studied. In particular, planar superconducting resonators are very sensitive to defects on their surfaces, such as two-level systems in oxidized metals and nonequilibrium quasiparticles, making these devices suitable probes for the different loss mechanisms. In this work, we present the design, fabrication, and characterization of Nb CPW resonators with different surface treatments with self-assembled monolayers (SAMs), which mitigate the growth of oxides in superconducting circuits. We demonstrate SAM-passivated resonators having internal quality factors of greater than 10 6 at a single-photon excitation power (measured at 100 mK), which were probed using scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy to demonstrate the efficiency of our surface treatment. Finally, we compared the improvements in the experimental quality factors to those obtained by numerical simulation.
In planar superconducting circuits, decoherence due to materials imperfections, especially two-level-system (TLS) defects at different interfaces, is a primary hurdle for advancing quantum computing and sensing applications. Traditional methods for mitigating TLS loss, such as etching oxide layers at metal and substrate interfaces, have proven to be inadequate due to the persistent challenge of oxide regrowth. In this work, we introduce a novel approach that employs molecular self-assembled monolayers (SAMs) to chemically bind at different interfaces of superconducting circuits. This technique is specifically tested here on coplanar waveguide (CPW) resonators, in which this method not only impedes oxide regrowth after surface etching but can also tailors the dielectric properties at different resonators interfaces. The deployment of SAMs results in a consistent improvement in the measured quality factors across multiple resonators, surpassing those with only oxide-etched resonators. The efficiency of our approach i3s supported by microwave measurements of multiple devices conducted at millikelvin temperatures and correlated with detailed X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) characterizations of SAM-passivated resonators. The compatibility of SAMs materials with the established fabrication techniques offers a promising route to improve the performance of superconducting quantum devices.
In planar superconducting quantum circuits, two-level system (TLS) defects within amorphous dielectrics at various circuit interfaces, including substrate–metal (SM) and air-interfaces, are a critical source of decoherence. We employed molecular self-assembled monolayer (SAM) at different interfaces to mitigate TLS losses in superconducting coplanar waveguide (CPW) resonators. Previous work has reported an increase in the resonator quality factor when a SAM is applied to air-interfaces, but a contrasting decrease is observed when the SAM is applied to the metal–substrate interfaces. To investigate the reason behind this decrease, we fabricated and characterized niobium (Nb)-based CPW resonator chips on silicon substrates, both with and without a SAM at the SM interface. Quality factor measurements performed at 100 mK across a wide range of driving powers confirmed that the presence of the SAM at the SM interface led to a reduction in the quality factor. This observed decrease is attributed to an increased TLS defect density, as suggested by the topography of niobium deposited on the SAM. Our findings demonstrate that the roughness of the deposited Nb at the SM interface, which is influenced by the SAM, significantly impacts the density of TLS defects at this interface. Furthermore, simulations of TLS losses in CPW resonators supported our experimental observations by evaluating resonator quality factors under various interface modifications, particularly showing a decrease in the quality factor when the SM interface exhibited high loss.
Tantalum is a promising platform for superconducting quantum circuits, yet coherence times remain limited by dielectric losses from interfacial two-level systems (TLS), exacerbated by native oxide regrowth. Here, we implement molecular surface passivation using self-assembled organic monolayers on freshly etched tantalum and silicon in coplanar waveguide resonators. Surface characterization by contact angle, XPS, FTIR and TEM confirm the formation of ordered, nanometer-thick films that suppress oxide formation. Microwave measurements in the ~5-9 GHz range reveal internal quality factors up to 1.8x10^6 in the single-photon regime at 100 mK, representing a ~140% improvement over untreated devices with native oxide. Power and temperature dependent measurements attribute this enhancement to reduced TLS-induced losses. These results demonstrate that molecular passivation effectively engineers low-loss interfaces and provides a scalable route toward high-coherence superconducting quantum devices.
Superconducting coplanar waveguide resonators are essential components in quantum processors, where their internal quality factor (Qi) constrains qubit coherence and readout fidelity. In niobium devices, microwave losses at millikelvin temperatures are strongly influenced by two-level systems (TLS) associated with the complex NbOx surface oxide. To mitigate these losses, we investigate a surface-engineering approach in which Nb films are capped in situ with a thin tantalum layer to suppress Nb2O5 formation and replace the native NbOx interface with a Ta-based oxide. We fabricate Nb/Ta bilayer and reference Nb resonators on high-resistivity silicon using identical DC sputtering and wet etching conditions, and characterize their performance at millikelvin temperatures. Fresh Ta-encapsulated devices exhibit internal quality factors up to 2.4 x 10^6 in the near-single-photon regime, with power dependence consistent with reduced TLS-related loss at the metal-air interface. A control Nb device fabricated under the same process shows comparatively lower Q_TLS, consistent with the beneficial effect of the Ta capping layer. Furthermore, ageing tests performed on Nb/Ta resonators after six months reveal a moderate reduction in Q_TLS relative to their initial values, yet the performance remains superior to newly fabricated Nb-only devices. These results suggest that thin Ta encapsulation enhances interface quality and contributes to improved temporal stability while remaining compatible with Nb-based fabrication workflows.
Abstract One main limiting factor towards achieving high coherence times in superconducting circuits is two-level system (TLS) losses. Mitigating such losses requires controlling the formation of native oxides at the metal-air interface. Here, we report the growth of alkyl-phosphonate self-assembled monolayers (SAMs) on Nb thin films following oxide removal. The impact of passivation was evaluated via the performance of coplanar waveguide resonators at 10 mK, in terms of quality factor and resonant frequency, over six days of air exposure. Un-passivated resonators exhibited an ~80% increase in loss at single-photon power levels, whereas SAM-passivated resonators maintained excellent temporal stability, attributed to suppressed oxide regrowth. By employing a two-component TLS model, we discern distinct prominent loss channels for each resonator type and quantified the characteristic TLS loss of the SAMs to be ~5×10 -7 . We anticipate our passivation methodology to offer a promising route toward industrial-scale qubit fabrication, particularly where long-term device stability is critical.
The native oxide layer formed on aluminum (Al) surfaces in superconducting quantum circuits is a significant source of two-level system defects, which couple with electric fields and degrade quantum coherence. Recent research has explored etching, encapsulation, and other surface treatments as potential strategies to mitigate the formation of oxides at air interfaces in these circuits. This study demonstrates a novel approach to passivate the Al–air interface using a molecular self-assembled monolayer (SAM). Freshly prepared Al thin films were passivated with SAMs by immersing the Al-coated silicon substrates in SAM solutions. X-ray photoelectron spectroscopy (XPS) confirms the successful binding of the SAM and the absence of further aluminum oxide growth. Moreover, the passivation remains stable after aging for 15 days in ambient conditions, as evidenced by XPS and contact angle measurements. Scanning electron microscopy analyses further support the binding of the SAM to the Al surface and mitigation of oxide growth. These findings suggest that SAM-based passivation offers a promising method for reducing microwave loss and improving the performance of Al-based superconducting quantum circuits.