title: Improving the coherence time of a quantum system via a coupling to a short-lived system.
abstract: In this Letter, we propose a counterintuitive use of a hybrid system where the coherence time of a quantum system can be significantly improved by coupling it with a system of a shorter coherence time. Coupling a two-level system with a single nitrogen-vacancy (NV^{-}) center, a dark state of the NV^{-} center naturally forms after the hybridization. We show that this dark state becomes robust against noise due to the coupling even when the coherence time of the two-level system is much shorter than that of the NV^{-} center. Our proposal opens a new way to use a quantum hybrid system for the realization of robust quantum information processing.
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: Yuichiro
authors: Y
authors: Matsuzaki
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: Xiaobo
authors: X
authors: Zhu
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: Kosuke
authors: K
authors: Kakuyanagi
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: Hiraku
authors: H
authors: Toida
authors: Graduate School of Engineering Science, University of Osaka, 1-3 Machikane-yama, Toyonaka, Osaka 560-8531, Japan.
authors: Takaaki
authors: T
authors: Shimo-Oka
authors: Graduate School of Engineering Science, University of Osaka, 1-3 Machikane-yama, Toyonaka, Osaka 560-8531, Japan.
authors: Norikazu
authors: N
authors: Mizuochi
authors: National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan.
authors: Kae
authors: K
authors: Nemoto
authors: National Institute of Information and Communications Technology, Koganei, Tokyo 184-8795, Japan.
authors: Kouichi
authors: K
authors: Semba
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: William J
authors: WJ
authors: Munro
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: Hiroshi
authors: H
authors: Yamaguchi
authors: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors: Shiro
authors: S
authors: Saito