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arXiv:2010.12090 · Review of Scientific Instruments

Ultrahigh vacuum packaging and surface cleaning for quantum devices

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

Published Feb 1, 2021• 14 citations
arXivHTMLPDF

Abstract

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 T1 = 84 µs and T2echo=134 μs after vacuum-loading these samples into a bottom loading dilution refrigerator in the UHV-package.

DOI
10.1063/5.0034574

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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 T1 = 84 µs and T2echo=134 μs after vacuum-loading these samples into a bottom loading dilution refrigerator in the UHV-package.
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Packages capable of supporting large arrays of high-coherence superconducting qubits are vital for the realisation of fault-tolerant quantum computers and the necessary high-throughput metrology required to optimise fabrication and manufacturing processes. We present a wafer-scale packaging architecture supporting over 500 qubits on a single 3-inch die. The package is engineered to suppress parasitic RF modes, and to mitigate material loss through simulation-informed design while managing differential thermal contraction to ensure robust operation at millikelvin temperatures. System-level heat-load calculations from a large wiring payload show this package may be operated in commercial dilution refrigerators. Measurements of the qubits loaded into the package show median T1T_1T1​, T2e∼100 μT_{2e} \sim 100~μT2e​∼100 μs ($\sim$100 qubits) alongside readout with median fidelity of 97.5% (54 qubits) and a median qubit temperature of 36 mK (54 qubits). These results validate the performance of these packages and demonstrate that large-scale integration can be achieved without compromising device performance. Finally, we highlight the utility of these packages as a tool for high throughput feedback on qubit figures of merit over large sample sizes, allowing identification of performance outliers in the tails of the coherence distribution, a critical capability for informing fabrication and manufacture of high-quality quantum qubits and quantum processors.
We present the design and vacuum performance of a compact room-temperature trapped ion system for quantum computing, consisting of an ultra-high vacuum (UHV) package, a micro-fabricated surface trap, and a small form-factor ion pump. The system is designed to maximize mechanical stability and robustness by minimizing the system size and weight. The internal volume of the UHV package is only ≈2 cm3, a significant reduction in comparison with conventional vacuum chambers used in trapped ion experiments. We demonstrate trapping of 174Yb+ ions in this system and characterize the vacuum level in the UHV package by monitoring both the rates of ion hopping in a double-well potential and ion chain reordering events. The calculated pressure in this vacuum package is ≈2.2×1011 Torr, which is sufficient for the majority of current trapped ion experiments.
We have developed a low temperature (LT), ultra-high-vacuum (UHV) system that combines two complementary techniques, scanning probe microscopy (SPM) and electrical transport measurements, within a single platform. By providing simultaneous access to the atomic-scale surface landscape and the macroscopic device response of the same sample, the setup enables direct correlations between local structural/spectroscopic signatures and global electronic transport behavior in two-dimensional (2D) devices. The system allows experiments where atomic-scale modifications or controlled manipulations are performed while continuously monitoring their impact on device-scale performance. The setup consists of two interconnected UHV chambers: a dedicated preparation chamber and a separate measurement chamber that houses a liquid-helium cryostat and the SPM/transport stage. Base pressure is 1x10^-11 Torr. A key feature is direct optical access to the sample, enabling rapid and reliable tip positioning with an accuracy of 5 microns x 5 microns within 10 minutes. The SPM, operated using custom-built electronics, can track the exact same sample region across a temperature range from 2.9 K to 400 K, with mechanical stability below 1 pm. System performance is demonstrated on graphene devices, and bulk Pb is used to determine energy resolution. Using superconducting tips, scanning tunneling spectroscopy measures the superconducting gap with an energy resolution of 30 microV. Transport measurements track the temperature dependence of both resistivity and critical current across the superconducting transition of an in-situ prepared Pb nanowire.
Cryogenic environments benefit ion trapping experiments by offering lower motional heating rates, collision energies, and an ultrahigh vacuum (UHV) environment for maintaining long ion chains for extended periods of time. Mechanical vibrations caused by compressors in closed-cycle cryostats can introduce relative motion between the ion and the wavefronts of lasers used to manipulate the ions. Here, we present a novel ion trapping system where a commercial low-vibration closed-cycle cryostat is used in a custom monolithic enclosure. We measure mechanical vibrations of the sample stage using an optical interferometer, and observe a root-mean-square relative displacement of 2.4 nm and a peak-to-peak displacement of 17 nm between free-space beams and the trapping location. We packaged a surface ion trap in a cryopackage assembly that enables easy handling while creating a UHV environment for the ions. The trap cryopackage contains activated carbon getter material for enhanced sorption pumping near the trapping location, and source material for ablation loading. Using171^{171}171Yb+^{+}+as our ion, we estimate the operating pressure of the trap as a function of package temperature using phase transitions of zig-zag ion chains as a probe. We measured the radial mode heating rate of a single ion to be 13 quanta/s on average. The Ramsey coherence measurements yield 330-ms coherence time for counter-propagating Raman carrier transitions using a 355-nm mode-locked pulse laser, demonstrating the high optical stability.
Cryogenic microwave measurement of superconducting quantum devices is complicated by the packaging required to connect devices to control and readout circuitry. In this work, we outline the design and experimental demonstration of a wirebond-free, PCB-free, drop-in microwave package for on-chip superconducting quantum devices. The package is composed of a superconducting aluminum cavity with a suspended tungsten transmission pin. The fundamental package cavity mode is far detuned from the 4 GHz to 8 GHz band of interest, and the pin transmission exhibits less than 3 dB of ripple across this range. We demonstrate the use of this package to extract the loss tangent of superconducting ring resonators, measuring a value of (1.10 +- 0.09) x 10^-6, which agrees with measurements of lambda/4 resonators in wirebond-based packaging. This high-throughput measurement system will allow the rapid generation of large datasets for improving superconducting qubit performance, and facilitate time-sensitive surface passivation and oxide regrowth studies.