Argon-Milling-Induced Decoherence Mechanisms in Superconducting Quantum Circuits

Damme, Jacques Van; Ivanov, Ts.; Favia, P.; Conard, Thierry; Verjauw, J.; Acharya, R.; Lozano, Daniel Pérez; Raes, Bart; Vondel, J. Van de; Vadiraj, A.M.; Mongillo, Massimo; Wan, Danny; Boeck, J. De; Potočnik, Anton; Greve, K. De

doi:10.1103/physrevapplied.20.014034

Cited by 3 publications

References 58 publications

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Improved Interface of Niobium Superconducting Resonator with Ruthenium as a Capping Layer

Karuppannan,

Huang,

Kommanaboina

et al. 2024

ACS Appl. Electron. Mater.

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The current performance of superconducting circuit-based quantum processors is limited by the poor understanding of interface physics, including native surface oxide formation on the superconducting metal, which causes two-level system (TLS) loss. Niobium (Nb), a superconducting metal with a high energy gap, is an ideal choice for superconducting processors, but unfortunately, it is marred by TLS. Several methods have been proposed to minimize surface oxide on the Nb film, and considerable improvement in TLS loss has been demonstrated. These methods include surface passivation through metal capping, self-assembly of organic molecules, and post-cleaning processes. Among these, metal capping is a suitable choice despite forming a 3−5 nm thick oxide, as self-assembly and post-treatment do not protect the Nb film surface during further fabrication. Here, we have proposed ruthenium (Ru) as a capping layer, forming a self-limiting oxidation with a 0.6 nm oxide thickness and predominantly producing fewer oxide compositions while being chemically resistant for further wafer fabrication processes, thus fulfilling all the criteria of an ideal capping layer. Our investigation suggests that Nb/Ru resonators have great potential as versatile and promising tools for advancing superconducting quantum technologies and integrating quantum interconnects into qubits with minimized TLS loss.

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Improved Interface of Niobium Superconducting Resonator with Ruthenium as a Capping Layer

Karuppannan,

Huang,

Kommanaboina

et al. 2024

ACS Appl. Electron. Mater.

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Advanced CMOS manufacturing of superconducting qubits on 300 mm wafers

Van Damme,

Massar,

Acharya

et al. 2024

Nature

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The development of superconducting qubit technology has shown great potential for the construction of practical quantum computers1,2. As the complexity of quantum processors continues to grow, the need for stringent fabrication tolerances becomes increasingly critical3. Utilizing advanced industrial fabrication processes could facilitate the necessary level of fabrication control to support the continued scaling of quantum processors. However, at present, these industrial processes are not optimized to produce high-coherence devices, nor are they a priori compatible with the approaches commonly used to make superconducting qubits. Here we demonstrate superconducting transmon qubits manufactured in a 300 mm complementary metal–oxide–semiconductor (CMOS) pilot line using industrial fabrication methods, with resulting relaxation and coherence times exceeding 100 μs. We show across-wafer, large-scale statistics of coherence, yield, variability and ageing that confirm the validity of our approach. The presented industry-scale fabrication process, which uses only optical lithography and reactive-ion etching, has a performance and yield in line with conventional laboratory-style techniques utilizing metal lift-off, angled evaporation and electron-beam writing4. Moreover, it offers the potential for further upscaling through three-dimensional integration5 and more process optimization. This result marks the advent of an alternative and new, large-scale, truly CMOS-compatible fabrication method for superconducting quantum computing processors.

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Impact of surface roughness on consistent resonator performance

Karuppannan,

Kommanaboina,

Utama

et al. 2024

Preprint

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Superconducting circuit-based quantum processors are leading platforms for quantum computing. In these circuits, microwave photons are stored as qubits in ultra-low-loss planar resonators and non-linear inductors formed by Josephson junctions. Resonators are typically made from high-energy-gap superconductors like Nb or Ta, while junctions are made of Al. Resonators occupy much of the circuit, making defect-free fabrication and understanding microwave energy dissipation crucial. Losses arise from noise, two-level systems (TLS), quasi-particles, and impurities. TLS losses dominate at operating temperatures below the critical temperature of the metal, whereas photon loss due to quasi-particles, often stemming from grain boundaries and pinholes in the metal film, becomes more pronounced at higher photon numbers or temperatures approaching the metal's critical temperature. To mitigate these, substrate cleaning, surface control, and non-superconducting film capping prevent oxide formation and reduce impurities. High-frequency drives, coupled with impurities at grain boundaries, lead to nonuniform quality factors among resonators. By controlling oxygen plasma exposure to minimize surface roughness and pinhole depth, we observed an area-dependent quality factor, which we attribute to changes in surface resistivity. This approach minimized variations in quality factors across resonators, improving uniformity in Nb-based devices and more consistent qubit readout performance.

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Argon-Milling-Induced Decoherence Mechanisms in Superconducting Quantum Circuits

Cited by 3 publications

References 58 publications

Improved Interface of Niobium Superconducting Resonator with Ruthenium as a Capping Layer

Improved Interface of Niobium Superconducting Resonator with Ruthenium as a Capping Layer

Advanced CMOS manufacturing of superconducting qubits on 300 mm wafers

Impact of surface roughness on consistent resonator performance

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