# Physics Colloquium

*,*University of Tokyo

*,*

I was one of the original members of the QUIC project, which started at Caltech in 1996. I did quantum teleportation experiment under the guidance of Jeff Kimble as the activity of the project [1]. Also, I met a lot of brilliant people like Daniel Gottesman, Alexei Kitaev, and John Preskill, who invented so-called GKP qubits in 2001 [2]. Since then my bible is the GKP paper and I have been pursuing the realization of fault-tolerant large-scale quantum computers with GKP qubits. We succeeded in creation of large-scale cluster states in the time domain for universal quantum computing [3-5]. The cluster states can be regarded as "superposition of look-up tables", i.e., superposition of input-output relations. We can select one of them by using measurements. We can change the look-up table by changing the measurement basis. Here, the measurement result changes at random. So we have to make an "error correction" by using the measurement result. Since the procedure is exactly the same as quantum teleportation, we can regard this quantum computation with a cluster state as sequential quantum teleportation, which is my favorite. I will show our activities for the realization of fault-tolerant large-scale quantum computers with GKP qubits in the colloquium.

[1] A. Furusawa, J. L. Sorensen, S. L. Braunstein, C. A. Fuchs, H. J. Kimble, and E. S. Polzik,Science 282, 706 (1998).

[2] D. Gottesman, A. Kitaev, and J. Preskill, Phys. Rev. A 64, 012310 (2001).

[3] S. Yokoyama, R. Ukai, S. C. Armstrong, C. Sornphiphatphong, T. Kaji, S. Suzuki, J. Yoshikawa, H. Yonezawa, N. C. Menicucci, and A. Furusawa, Nature Photonics 7, 982 (2013).

[4] J. Yoshikawa, S. Yokoyama, T. Kaji, C. Sornphiphatphong, Y. Shiozawa, K. Makino, and A. Furusawa, APL Photonics 1, 060801 (2016).

[5] W. Asavanant, Y. Shiozawa, S. Yokoyama, B. Charoensombutamon, H. Emura, R. N. Alexander, S. Takeda, J. Yoshikawa, N. C. Menicucci, H. Yonezawa, and A. Furusawa, Science 366, 373 (2019).

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