Substrate surface engineering for high-quality silicon/aluminum superconducting resonators
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Bibliographic record
Abstract
Abstract Quantum bits (qubits) with long coherence times are an important element for the implementation of medium- and large-scale quantum computers. In the case of superconducting planar qubits, understanding and improving qubits’ quality can be achieved by studying superconducting planar resonators. In this paper, we fabricate and characterize coplanar waveguide resonators made from aluminum thin films deposited on silicon substrates. We perform three different substrate surface treatments prior to aluminum deposition: one chemical treatment based on a hydrofluoric acid clean; one physical treatment consisting of a thermal annealing at 880 °C in high vacuum; and one combined treatment comprising both the chemical and the physical treatments. The aim of these treatments is to remove the two-level state (TLS) defects hosted by the native oxides residing at the various samples’ interfaces. We first characterize the fabricated samples through cross-sectional tunneling electron microscopy, acquiring electron energy loss spectroscopy maps of the samples’ cross sections. These measurements show that both the chemical and the physical treatments almost entirely remove native silicon oxide from the substrate surface and that their combination results in the cleanest interface. Additionally, we analyze the effects of the various substrate treatments on the roughness of the silicon surface by means of atomic force microscopy surface morphology mapping. We then study the quality of the resonators by means of microwave measurements in the ‘quantum regime’, i.e., at a temperature T ∼ 10 mK and at a mean microwave photon number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">ph</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> </mml:math> . In this regime, we find that both surface treatments independently improve the resonator’s intrinsic quality factor by ≈172%. The highest quality factor is obtained for the combined treatment, Q i ≈ 0.82 million, corresponding to an improvement by ≈256%. Finally, we find that the TLS quality factor averaged over a time period of 3 h is ∼3 million at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">ph</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>∼</mml:mo> <mml:mn>10</mml:mn> </mml:math> , indicating that substrate surface engineering can potentially reduce the TLS loss below other losses such as quasiparticle loss and flux noise.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it