Localization and Mitigation of Loss in Niobium Superconducting Circuits

Altoé, M. Virginia P.; Banerjee, Archan; Berk, Cassidy; Hajr, Ahmed; Schwartzberg, Adam; Song, Chengyu; Alghadeer, Mohammed; Aloni, Shaul; Elowson, Michael J.; Kreikebaum, John Mark; Wong, Ed; Griffin, Sinéad M.; Rao, Saleem G.; Weber‐Bargioni, Alexander; Minor, Andrew M.; Santiago, David I.; Cabrini, Stefano; Siddiqi, Irfan; Ogletree, D. Frank

doi:10.1103/prxquantum.3.020312

Cited by 43 publications

(26 citation statements)

References 62 publications

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“…In addition, Figure a shows that the sample cleaned with BOE still had a higher δ int than that of the sample cleaned with BOE and passivated with SAM after fabrication. This is because of the regrowth process of oxide layers on surfaces and interfaces of the resonators on the exposure of the sample to the ambient environment after cleaning by BOE and before loading into the ADR (approximately 1 h for wire bonding and packaging before the sample is loaded under vacuum inside the ADR (see the Materials and Methods section)) . The microwave signals at low and high powers for the four devices are shown in Figure b,c, respectively.…”

Section: Resultsmentioning

confidence: 99%

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

Alghadeer

Banerjee

Hajr

et al. 2022

ACS Appl. Mater. Interfaces

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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 singlephoton 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.

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Section: Resultsmentioning

confidence: 99%

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

Alghadeer

Banerjee

Hajr

et al. 2022

ACS Appl. Mater. Interfaces

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“…XPS is now commonly used to identify the presence of superconductor surface oxides in qubit circuits. Recent works include investigating the presence of Nb [48][49][50], NbTi [51], NbTiN [13], TiN [52], Al [52] and Ta [35,36] oxides, and how the oxide regrows [50]. The oxide presence, processing steps or surface treatments can then be correlated with resonator quality factor measurements [49,50,52,53].…”

Section: Surface Analysis Applied To Superconducting Quantum Circuitsmentioning

confidence: 99%

“…Worth mentioning here is also electron back-scattered diffraction, a SEM-based analogous technique, which avoids any structural damage induced by the preparation of TEM samples. Electron energy loss spectroscopy (EELS) is a useful technique for investigating interfaces for information on local chemical composition and bonding mechanisms [49,64]. It has been applied to study the influence of substrate treatments, where the presence of oxides can be correlated resonator loss, most notably recently carried out for Al [41] and Nb [48,49,69].…”

Section: Surface Analysis Applied To Superconducting Quantum Circuitsmentioning

confidence: 99%

“…Electron energy loss spectroscopy (EELS) is a useful technique for investigating interfaces for information on local chemical composition and bonding mechanisms [49,64]. It has been applied to study the influence of substrate treatments, where the presence of oxides can be correlated resonator loss, most notably recently carried out for Al [41] and Nb [48,49,69]. Alternatively, x-ray fluorescence and AES could also be used for chemical composition and are typically much more efficient than EELS.…”

Section: Surface Analysis Applied To Superconducting Quantum Circuitsmentioning

confidence: 99%

“…XPS combined with resonant inelastic x-ray scattering, using a synchrotron x-ray source, was used to investigate the composition of Nb surface oxides in transmon circuits, revealing a correlation between qubit relaxation times and grain size, grain boundary oxygen diffusion and the amount of near-surface oxides [74]. Combining XPS with TEM and EELS [49] or RBS [75] can provide further details about the structure and presence of surface oxides and the composition of materials [75]. High-coherence tantalum circuits were also recently studied by x-ray diffraction, energy-dispersive x-ray spectroscopy, TEM, XPS and AFM [35].…”

Section: Surface Analysis Applied To Superconducting Quantum Circuitsmentioning

confidence: 99%

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Chemical and structural identification of material defects in superconducting quantum circuits

Graaf

Un²,

Shard³

et al. 2022

Mater. Quantum. Technol.

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Quantum circuits show unprecedented sensitivity to external fluctuations compared to their classical counterparts, and it can take as little as a single atomic defect somewhere in a mm-sized area to completely spoil device performance. For improved device coherence it is thus essential to find ways to reduce the number of defects, thereby lowering the hardware threshold for achieving fault-tolerant large-scale error-corrected quantum computing. Given the evasive nature of these defects, the materials science required to understand them is at present in uncharted territories, and new techniques must be developed to bridge existing capabilities from materials science with the needs identified by the superconducting quantum circuit community. In this paper, we give an overview of methods for characterising the chemical and structural properties of defects in materials relevant for superconducting quantum circuits. We cover recent developments from in-operation techniques, where quantum circuits are used as probes of the defects themselves, to in situ analysis techniques and well-established ex situ materials analysis techniques. The latter is now increasingly explored by the quantum circuits community to correlate specific material properties with qubit performance. We highlight specific techniques which, given further development, look especially promising and will contribute towards a future toolbox of material analysis techniques for quantum.

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Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Torres‐Castanedo,

Goronzy,

Pham

et al. 2024

Adv Funct Materials

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Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride‐based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary‐ion mass spectrometry, X‐ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb2O5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power‐independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two‐level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

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Localization and Mitigation of Loss in Niobium Superconducting Circuits

Cited by 43 publications

References 62 publications

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

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

Chemical and structural identification of material defects in superconducting quantum circuits

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

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