Related papers: Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate

Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate

URL: http://arxiv.org/abs/2103.07711v3
Date: Tue, 12 Oct 2021 01:32:02 GMT
Title: Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate
Authors: Sunmi Kim, Hirotaka Terai, Taro Yamashita, Wei Qiu, Tomoko Fuse, Fumiki Yoshihara, Sahel Ashhab, Kunihiro Inomata, and Kouichi Semba
Abstract summary: We develop superconducting qubits based on NbN/AlN/NbN epitaxial Josephson junctions on silicon substrates. The all-nitride qubits have great advantages such as chemical stability against oxidation.
Score: 2.3180219011095327
License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
Abstract: Improving the coherence of superconducting qubits is a fundamental step towards the realization of fault-tolerant quantum computation. However, coherence times of quantum circuits made from conventional aluminium-based Josephson junctions are limited by the presence of microscopic two-level systems in the amorphous aluminum oxide tunnel barriers. Here, we have developed superconducting qubits based on NbN/AlN/NbN epitaxial Josephson junctions on silicon substrates which promise to overcome the drawbacks of qubits based on Al/AlO$_{x}$/Al junctions. The all-nitride qubits have great advantages such as chemical stability against oxidation, resulting in fewer two-level fluctuators, feasibility for epitaxial tunnel barriers that reduce energy relaxation and dephasing, and a larger superconducting gap of $\sim$5.2 meV for NbN, compared to $\sim$0.3 meV for aluminium, which suppresses the excitation of quasiparticles. By replacing conventional MgO by a silicon substrate with a TiN buffer layer for epitaxial growth of nitride junctions, we demonstrate a qubit energy relaxation time $T$$_{1}$=16.3 $\mu$s and a spin-echo dephasing time $T$$_{2}$=21.5 $\mu$s. These significant improvements in quantum coherence are explained by the reduced dielectric loss compared to previously reported NbN-based qubits with MgO substrates ($T$$_{1}$$\approx$$T$$_{2}$$\approx$0.5 $\mu$s). These results are an important step towards constructing a new platform for superconducting quantum hardware.

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