Side-wall spacer passivated sub-<i>μ</i>m Josephson junction fabrication process

The coherence of state-of-the-art superconducting qubit devices is predominantly limited by two-level-system defects, found primarily at amorphous interface layers. Reducing microwave loss from these interfaces by proper surface treatments is key to push the device performance forward. Here, we study niobium resonators after removing the native oxides with a hydrofluoric acid etch. We investigate the reappearance of microwave losses introduced by surface oxides that grow after exposure to the ambient environment. We find that losses in quantum devices are reduced by an order of magnitude, with internal Qfactors reaching up to 7×10 6 in the single photon regime, when devices are exposed to ambient conditions for 16 min. Furthermore, we observe that Nb2O5 is the only surface oxide that grows significantly within the first 200 hours, following the extended Cabrera-Mott growth model. In this time, microwave losses scale linearly with the Nb2O5 thickness, with an extracted loss tangent tanδNb2O5 = 9.9×10 -3 . Our findings are of particular interest for devices spanning from superconducting qubits, quantum-limited amplifiers, microwave kinetic inductance detectors to single photon detectors.

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“…Nb is widely used to fabricate superconducting devices [8], [11]- [15]. Its advantage over other superconducting metals (e.g.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Microwave Loss Induced by Oxide Regrowth in High- Q Niobium Resonators

et al. 2021

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“…Device fabrication. The devices are fabricated in a multi-layer process for superconducting circuits, the key element of which is a sidewall-passivated-spacer (SWAPS) technique 38 for the Nb-Al/AlO x -Nb Josephson junctions. Figures 1b and S1 summarize the structure of the device.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, an oscillator for a desired power level and a given frequency may be optimized by choosing I c accordingly. Technologically, the range of available critical currents spans several orders of magnitude 38 . Note that the maximum power output is obtained by optimizing the load such that R 1 ≈ 0.68 πI C Φ 0 C 2 s ω 3 and minimizing the residual microwave losses such that…”

Section: Theory and Designmentioning

confidence: 99%

A low-noise on-chip coherent microwave source

Yan,

Hassel,

Vesterinen

et al. 2021

Preprint

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The increasing need for scaling up quantum computers operating in the microwave domain calls for advanced approaches for control electronics. To this end, integration of components at cryogenic temperatures hosting also the quantum devices seems tempting. However, this comes with the limitations of ultra-low power dissipation accompanied by stringent signalquality requirements to implement quantum-coherent operations. Here, we present a device and a technique to provide coherent continuous-wave microwave emission. We experimentally verify that its operation characteristics accurately follow our introduced theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. From phase noise measurements, we evaluate that the infidelity of typical quantum gate operations owing to this cryogenic source is less than 0.1% up to 10-ms evolution times, which is well below the infidelity caused by dephasing of the state-of-the-art superconducting qubits. Our device provides a coherent tone of 25 pW, corresponding to the total power needed in simultaneous control of thousands of qubits. Thus, together with future cryogenic amplitude and phase modulation techniques, our results may open pathways for scalable cryogenic control systems for quantum processors.

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“…We have fabricated the devices with a superconducting multilayer process that has been detailed in Ref. [30]. Besides JPAs, the same process has produced functional TWPAs [15] as well as Josephson oscillators [31] featuring niobium trilayer JJs on a high-resistivity silicon substrate.…”

Section: Fabricationmentioning

confidence: 99%

A Sub-GHz Impedance-Engineered Parametric Amplifier for the Readout of Sensors and Quantum Dots

Vesterinen

Simbierowicz

Jabdaraghi

et al. 2022

IEEE Trans. Appl. Supercond.

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In the work on superconducting parametric amplifiers, the frequency band below one gigahertz is calling for systematic improvements. Despite a prospect for ultralow added noise, bandwidth limitations have slowed down the integration of such amplifiers into sub-GHz experiments demanding fast (< 1 µs) readout speeds. Here, we study the impedance engineering of a flux-driven Josephson parametric amplifier (JPA) at 600 MHz. We propose, simulate and experimentally demonstrate a partially reconfigurable impedance transformer. The transformer enhances the JPA bandwidth to a state-ofthe-art value of 10 MHz at 20 dB gain. Our amplifier has immediate applications in the readout of cryogenic sensors and in the reflectometry of quantum dots for spin qubit quantum computing.

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Side-wall spacer passivated sub-μm Josephson junction fabrication process

Cited by 25 publications

References 28 publications

Investigation of Microwave Loss Induced by Oxide Regrowth in High- Q Niobium Resonators

Investigation of Microwave Loss Induced by Oxide Regrowth in High- Q Niobium Resonators

A low-noise on-chip coherent microwave source

A Sub-GHz Impedance-Engineered Parametric Amplifier for the Readout of Sensors and Quantum Dots

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