As the field of superconducting quantum computing advances from the few-qubit stage to larger-scale processors, qubit addressability and extensibility will necessitate the use of 3D integration and packaging. While 3D integration is well-developed for commercial electronics, relatively little work has been performed to determine its compatibility with high-coherence solid-state qubits. Of particular concern, qubit coherence times can be suppressed by the requisite processing steps and close proximity of another chip. In this work, we use a flip-chip process to bond a chip with superconducting flux qubits to another chip containing structures for qubit readout and control. We demonstrate that high qubit coherence (T1, T2,echo>20μs) is maintained in a flip-chip geometry in the presence of galvanic, capacitive, and inductive coupling between the chips.
@article{arxiv.1706.04116,
title = {3D integrated superconducting qubits},
author = {D. Rosenberg and D. Kim and R. Das and D. Yost and S. Gustavsson and D. Hover and P. Krantz and A. Melville and L. Racz and G. O. Samach and S. J. Weber and F. Yan and J. Yoder and A. J. Kerman and W. D. Oliver},
journal= {arXiv preprint arXiv:1706.04116},
year = {2018}
}