@article{14517,
  abstract     = {State-of-the-art transmon qubits rely on large capacitors, which systematically improve their coherence due to reduced surface-loss participation. However, this approach increases both the footprint and the parasitic cross-coupling and is ultimately limited by radiation losses—a potential roadblock for scaling up quantum processors to millions of qubits. In this work we present transmon qubits with sizes as low as 36 × 39 µm2 with  100-nm-wide vacuum-gap capacitors that are micromachined from commercial silicon-on-insulator wafers and shadow evaporated with aluminum. We achieve a vacuum participation ratio up to 99.6% in an in-plane design that is compatible with standard coplanar circuits. Qubit relaxationtime measurements for small gaps with high zero-point electric field variance of up to 22 V/m reveal a double exponential decay indicating comparably strong qubit interaction with long-lived two-level systems. The exceptionally high selectivity of up to 20 dB to the superconductor-vacuum interface allows us to precisely back out the sub-single-photon dielectric loss tangent of aluminum oxide previously exposed to ambient conditions. In terms of future scaling potential, we achieve a ratio of qubit quality factor to a footprint area equal to 20 µm−2, which is comparable with the highest T1 devices relying on larger geometries, a value that could improve substantially for lower surface-loss superconductors. },
  author       = {Zemlicka, Martin and Redchenko, Elena and Peruzzo, Matilda and Hassani, Farid and Trioni, Andrea and Barzanjeh, Shabir and Fink, Johannes M},
  issn         = {2331-7019},
  journal      = {Physical Review Applied},
  number       = {4},
  publisher    = {American Physical Society},
  title        = {{Compact vacuum-gap transmon qubits: Selective and sensitive probes for superconductor surface losses}},
  doi          = {10.1103/PhysRevApplied.20.044054},
  volume       = {20},
  year         = {2023},
}

@article{13264,
  abstract     = {We build a parametric amplifier with a Josephson field-effect transistor (JoFET) as the active element. The resonant frequency of the device is field-effect tunable over a range of 2 GHz. The JoFET amplifier has 20 dB of gain, 4 MHz of instantaneous bandwidth, and a 1-dB compression point of -125.5 dBm when operated at a fixed resonance frequency.

},
  author       = {Phan, Duc T and Falthansl-Scheinecker, Paul and Mishra, Umang and Strickland, W. M. and Langone, D. and Shabani, J. and Higginbotham, Andrew P},
  issn         = {2331-7019},
  journal      = {Physical Review Applied},
  number       = {6},
  publisher    = {American Physical Society},
  title        = {{Gate-tunable superconductor-semiconductor parametric amplifier}},
  doi          = {10.1103/PhysRevApplied.19.064032},
  volume       = {19},
  year         = {2023},
}

@article{10940,
  abstract     = {Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum computing architectures involving spin or topological qubits and electromechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film three-dimensional aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can probe solely the effect of magnetic fields on the transmons. We present data on a single-junction and a superconducting-quantum-interference-device (SQUID) transmon that are cooled down in the same cavity. As expected, the transmon frequencies decrease with increasing field, due to suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic field resilience: both transmons display microsecond coherence up to at least 0.65 T, and T1 remains above 1μs over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are suitable hardware for superconducting circuits in the high-magnetic-field regime.},
  author       = {Krause, J. and Dickel, C. and Vaal, E. and Vielmetter, M. and Feng, J. and Bounds, R. and Catelani, G. and Fink, Johannes M and Ando, Yoichi},
  issn         = {2331-7019},
  journal      = {Physical Review Applied},
  number       = {3},
  publisher    = {American Physical Society},
  title        = {{Magnetic field resilience of three-dimensional transmons with thin-film Al/AlOx/Al Josephson junctions approaching 1 T}},
  doi          = {10.1103/PhysRevApplied.17.034032},
  volume       = {17},
  year         = {2022},
}