Day 1 Dec-2 2021
Session 2 14:45-15:30
Si platform for implementing spin-based quantum computing
RIKEN Center for Emergent Matter Science and RIKEN Center for Quantum Computing, Japan
Silicon (Si) is a promising platform for implementing spin-based quantum computing with qubits of electrons (or holes) in QDs, because the qubits in Si are capable of a long intrinsic decoherence time (> msec), a high temperature operation (> K), and compatiblity in device fabrication with semiconductor manufacturing. But improving the fidelity of these operations and increasing the qubit number are still challenges in realizing the fault-tolerant quantum computation.
I will first discuss how to improve the fidelities of single- and two-qubit gates, initialization and readout beyond the quantum error correction threshold, 99 %. For the single qubits the fidelity higher than 99.9% has been achieved  but yet limited to 98 % for the two-qubit gates . This is assigned to slow operation compared to the dephasing and noise coming from the exchange coupling of qubits. To deal with these problems we use a micro-magnet technique  for a Si/SiGe double QD to make fast the single spin qubit drive and finally achieve the two-qubit gate fidelity above 99% . For the initialization and readout we use a quantum non-demolition method to raise the fidelity above 99 % .
I will finally review recent efforts to scale up the qubit system based on the semiconductor technology.
 J. Yoneda, K. Takeda, T. Otsuka, T. Nakajima, M. R. Delbecq, G. Allison, T. Honda, T. Kodera, S. Oda, Y. Hoshi, N. Usami, K. M. Itoh, and S. Tarucha, Nat. Nanotechnol. 13, 102 (2018).
 W. Huang, C.H. Yang, K.W. Chan, T. Tanttu, B. Hensen, R.C.C. Leon, M.A. Fogarty, J.C.C. Hwang, F.E. Hudson, K.M. Itoh, A. Morello, A. Laucht, and A.S. Dzurak, Nature 569, 532 (2019).
 M. Pioro-Ladriere, T. Obata, Y. Tokura, Y. -S. Shin, T. Kubo, K. Yoshida, T. Taniyama, and S. Tarucha, Nat. Physics 4, 776 (2008).
 A. Noiri, K. Takeda, T. Nakajima, T. Kobayashi, A. Sammak, G. Scappucci, and S. Tarucha, arXiv: 2108.02626 (2021).
 J. Yoneda, K. Takeda, A. Noiri, T. Nakajima, S. Li, J. Kamioka, T. Kodera, and S. Tarucha, , Nature Commun. 11, 1144 (2020).
 K. Takeda, A. Noiri, T. Nakajima, J. Yoneda, T. Kobayashi, and S. Tarucha, Nat. Nanotechnol. 16, 965 (2021).
Seigo Tarucha received the B. E. and M. S. degrees in applied physics from the University of Tokyo in 1976 and 1978, respectively. He joined NTT Basic Research Laboratories in 1978 and received the Ph. D degree from the University of Tokyo in 1986. In 1998 he moved to the University of Tokyo as a professor in the Physics Department and then to the Applied Physics Department in 2005. In April 2019 he retired from the University of Tokyo and moved to RIKEN Center for Emergent Matter Science (CEMS). He has been running a research group in CEMS since 2013 and also working as a CEMS deputy director since 2018. He has been concurrently serving as a research team leader for RIKEN Center for Quantum Computing since April 2020. He was a guest scientist in Max-Planck-Institute (Stuttgart) in 1986 and 1987 and in Delft University in 1995. He is currently working on spin-based quantum computing and topological quantum computing. He received Japan IBM award in 1998, Kubo Ryogo award, Nishina award in 2002, National medal with purple ribbon in 2004, Leo Esaki Award in 2007, and Achievement award of Japan Applied Physics Society in 2018.