Superconducting phase qubits with shadow-evaporated Josephson junctions

We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricat...

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Published inChinese physics B Vol. 26; no. 6; pp. 61 - 65
Main Author 宿非凡 刘伟洋 徐晖凯 邓辉 李志远 田野 朱晓波 郑东宁 吕力 赵士平
Format Journal Article
LanguageEnglish
Published 01.06.2017
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Summary:We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.
Bibliography:We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.
Fei-Fan Su1,2, Wei-Yang Liu1,2, Hui-Kai Xu1,2, Hui Deng1, Zhi-Yuan Li1,3, Ye Tian1, Xiao-Bo Zhu4, Dong-Ning Zheng1, Li Lv1, Shi-Ping Zhao（ 1 Beifing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; 2 School of Physical Sciences, University of Chinese Academy of Sciences （CAS）, Beijing 100049, China; 3 National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China ; 4 CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China ;5 Collaborative Innovation Center of Quantum Matter, Beijing, China）
superconducting phase qubit, two-level system, decoherence, shadow evaporated junction
11-5639/O4
ISSN:1674-1056
2058-3834
DOI:10.1088/1674-1056/26/6/060308