Building Blocks of a Flip-Chip Integrated Superconducting Quantum Processor

TL;DR

This paper demonstrates the successful integration of superconducting transmon qubits into flip-chip modules, achieving high coherence and gate fidelities, and discusses design methods for scalable quantum processors.

Contribution

It introduces a flip-chip integration approach for superconducting qubits that maintains high performance and scalability for quantum processors.

Findings

Coherence times exceeding 90 microseconds.

Single-qubit gate fidelities over 99.9%.

Two-qubit gate fidelities above 98.6%.

Abstract

We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips -- one quantum chip and one control chip -- that are bump-bonded together. We demonstrate time-averaged coherence times exceeding $90\,\mu s$, single-qubit gate fidelities exceeding $99.9\%$, and two-qubit gate fidelities above $98.6\%$. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline state-of-the-art in single-chip, planar circuits. This integration technique can be extended to the realisation of quantum processors accommodating hundreds of qubits in one module as it offers adequate input/output wiring access to all qubits and couplers.