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arXiv:2012.01438 · PRX Quantum

Microwave Package Design for Superconducting Quantum Processors

Sihao Huang, Benjamin Lienhard, Greg Calusine, Antti P. Vepsäläinen, Jochen Braumüller, David K. Kim, Alexander J. Melville, Bethany M. Niedzielski, Jonilyn Yoder, Bharath Kannan, Terry P. Orlando, Simon Gustavsson, William D. Oliver

Published Apr 16, 2021• 71 citations
arXivHTMLPDF

Abstract

Solid-state qubits with transition frequencies in the microwave regime, such as superconducting qubits, are at the forefront of quantum information processing.However, high-fidelity, simultaneous control of superconducting qubits at even a moderate scale remains a challenge, partly due to the complexities of packaging these devices.Here, we present an approach to microwave package design focusing on material choices, signal line engineering, and spurious mode suppression.We describe design guidelines validated using simulations and measurements used to develop a 24-port microwave package.Analyzing the qubit environment reveals no spurious modes up to 11 GHz.The material and geometric design choices enable the package to support qubits with lifetimes exceeding 350 μs.The microwave package design guidelines presented here address many issues relevant for near-term quantum processors.

DOI
10.1103/prxquantum.2.020306

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Solid-state qubits with transition frequencies in the microwave regime, such as superconducting qubits, are at the forefront of quantum information processing.However, high-fidelity, simultaneous control of superconducting qubits at even a moderate scale remains a challenge, partly due to the complexities of packaging these devices.Here, we present an approach to microwave package design focusing on material choices, signal line engineering, and spurious mode suppression.We describe design guidelines validated using simulations and measurements used to develop a 24-port microwave package.Analyzing the qubit environment reveals no spurious modes up to 11 GHz.The material and geometric design choices enable the package to support qubits with lifetimes exceeding 350 μs.The microwave package design guidelines presented here address many issues relevant for near-term quantum processors.
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Abstract Superconducting qubits are multilevel micro-fabricated artificial atoms based on superconducting materials. They are mainly operated in the low microwave frequency range (2–8 GHz) and require to be cooled below 20 mK to maintain quantum coherence. They enable precise engineering of transition frequencies and coupling strengths, facilitating advancements in quantum information processing and light-matter interactions. The field has evolved from early devices, characterized by short coherence times, to modern architectures with improved noise resilience, scalability, and fidelity. Better performances have been achieved through innovations in materials, fabrication, control electronics, and circuit design, enabling qubits with millisecond coherence times and gate fidelities exceeding 99.9%. However, challenges remain in mitigating two-level system defects, scaling devices, and addressing the cryogenic and infrastructure needs of larger quantum processing units. Current research focuses on modular and scalable architectures, error correction, and application. The field’s progress highlights the potential for superconducting qubits to drive advancements in quantum computation.
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One of the challenges for building a quantum computer with superconducting qubits is being able to integrate a sufficient density of microwave lines in a cryogenic environment. Traditionally this has been limited by the pitch of SMA cables. When trying to go beyond this approach there are two problems to address. The first is outfitting a dilution refrigerator with enough lines to run from room temperature to the base temperature stage. The second is building a package for a quantum integrated circuit that houses enough microwave lines itself. We propose a solution to both of these problems by using RF flexible circuits to increase signal density in the dilution refrigerator and package while maintaining signal integrity. We also discuss the thermal, mechanical and RF considerations that go into designing such a system. Finally we show a proof-of-concept integration of the entire system including measurements with superconducting qubits.
Fault-tolerant superconducting quantum processors are limited by decoherence, limited connectivity, and the wiring burden at cryogenic temperatures. This review surveys superconducting “metamaterials”: circuits built from many repeating, deeply subwavelength building blocks (unit cells) that tailor dispersion, impedance, and bandgaps. By shaping the electromagnetic (and sometimes acoustic) environment of a qubit, these networks can suppress or enhance radiative decay and frequency shifts (Purcell and Lamb effects) and provide compact multimode structures for multiplexed control and photon-mediated coupling. We emphasize the practical trade-offs—added dielectric participation, fabrication disorder, and leakage through spurious chip/package modes—and the measurements needed to quantify them. The review summarizes design and tuning approaches (including Josephson/Superconducting Quantum Interference Device implementations), materials and fabrication limits, and mode-resolved benchmarks, and it highlights emerging directions such as topological lattices and engineered reservoirs while clearly separating demonstrations from proposals.