Effects of surface treatments on flux tunable transmon qubits

Mergenthaler, Matthias; Müller, Clemens; Ganzhorn, Marc; Paredes, Stephan; Müller, P.; Salis, G.; Adiga, Vivekananda P.; Brink, Markus; Sandberg, Martin; Hertzberg, Jared; Filipp, Stefan; Fuhrer, Andreas

doi:10.1038/s41534-021-00491-2

Cited by 14 publications

(8 citation statements)

References 61 publications

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“…Given an E J /E C -ratio of 27.3 and a corresponding residual charge dispersion of ε 0 = 23 kHz, our findings are compatible with the presence of quasiparticles but do not exclude two-level fluctuators as the source of the observed fluctuations. The measured coherence figures are on par with the best in literature and show that our UHV-package can be used to measure complex quantum device chips and study a variety of surface treatments 14 .…”

Section: Qubit Measurementssupporting

confidence: 59%

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Ultrahigh Vacuum Packaging and Surface Cleaning for Quantum Devices

Mergenthaler,

Paredes,

Müller

et al. 2020

Preprint

Self Cite

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We describe design, implementation and performance of an ultra-high vacuum (UHV) package for superconducting qubit chips or other surface sensitive quantum devices. The UHV loading procedure allows for annealing, ultra-violet light irradiation, ion milling and surface passivation of quantum devices before sealing them into a measurement package. The package retains vacuum during the transfer to cryogenic temperatures by active pumping with a titanium getter layer. We characterize the treatment capabilities of the system and present measurements of flux tunable qubits with an average T 1 = 84 µs and T echo 2 = 134 µs after vacuum-loading these samples into a bottom loading dilution refrigerator in the UHV-package.

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Section: Qubit Measurementssupporting

confidence: 59%

“…Measurements on high-coherence flux tunable qubits (T 1 = 84.3 µs and T echo 2 = 134.4 µs) demonstrate that the UHV package is capable of assessing coherence figures of merit as a function of treatment parameters for complex multi-qubit chips. This functionality is unique in the field and will be put to use in future work 14 .…”

Section: Discussionmentioning

confidence: 99%

Ultrahigh Vacuum Packaging and Surface Cleaning for Quantum Devices

Mergenthaler,

Paredes,

Müller

et al. 2020

Preprint

Self Cite

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“…Nevertheless, a large number of works have used this approach with varying degrees of success. Some recent examples include correlating in situ treatments with qubit coherence times [39,40], 1/f flux noise [21] in superconducting quantum interference devices (SQUIDs) and resonator loss and noise [25,41]. We refer to a recent review [1] for a more extensive overview of this approach.…”

Section: Understanding Tls Ensembles From Device Treatmentsmentioning

confidence: 99%

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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“…But for qubits operating at millikelvin temperatures, microwave-frequency loss has become an overarching criterion for building processors with sufficient coherence to entangle more than a few qubits 1 . The stringency of this requirement has drawn qubit fabrication into the domain of surface science, since the electromagnetic fields storing information interact with the interface between the solid state and atmosphere to a degree not usually met with in superconducting or conventional information processing devices [9][10][11][12] . Among superconductors being pursued for favorable surface properties 13 , tantalum shares desirable traits with niobium but has a distinct surface chemistry 14,15 , affording new possibilities for engineering low-loss interfaces with the substrate and atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

Alegria

Tennant

Chaves

et al. 2023

Preprint

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Building usefully coherent superconducting quantum processors depends on reducing losses in their constituent materials.1 Tantalum, like niobium, has proven utility as the primary superconducting layer within highly coherent qubits.2,3 But, unlike Nb, high temperatures are typically used to stabilize the desirable body-centered-cubic phase, α-Ta, during thin film deposition. It has long been known that a thin Nb layer permits the room-temperature nucleation of α-Ta,4-6 although neither an epitaxial process nor few-photon microwave loss measurements have been reported for Nb-nucleated Ta films prior to this study. We compare resonators patterned from Ta films grown at high temperature (500 °C) and films nucleated at room temperature, in order to understand the impact of crystalline order on quantum coherence. In both cases, films grew with Al2O3 (001) || Ta (110) indicating that the epitaxial orientation is independent of temperature and is preserved across the Nb/Ta interface. We use conventional low-power spectroscopy to measure two level system (TLS) loss, as well as an electric-field bias technique to measure the effective dipole moments of TLS in the surfaces of resonators. In our measurements, Nb-nucleated Ta resonators had greater loss tangent (1.5 ± 0.1 × 10-5) than nonnucleated (5 ± 1 × 10-6) in approximate proportion to defect densities as characterized by X-ray diffraction (0.27 ° vs 0.18 ° [110] reflection width) and electron microscopy (30 nm vs 70 nm domain size). The dependence of the loss tangent on domain size indicates that the development of more ordered Ta films is likely to lead to improvements in qubit coherence times.1,7 Moreover, lowtemperature α-Ta epitaxy may enable the growth of new, microstate-free heterostructures which would not withstand high temperature processing.8

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Effects of surface treatments on flux tunable transmon qubits

Cited by 14 publications

References 61 publications

Ultrahigh Vacuum Packaging and Surface Cleaning for Quantum Devices

Ultrahigh Vacuum Packaging and Surface Cleaning for Quantum Devices

Chemical and structural identification of material defects in superconducting quantum circuits

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

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