Göteborg Mesoscopic Lecture 2026

Titel: Rise of superconducting quantum circuits and superconducting Kerr parametric oscillators based Bosonic qubit

Talare: Jaw-Shen Tsai, National Yang Ming Chiao Tung University, Taiwan (previously at NEC, RIKEN, and Tokyo Univ Sci)

Abstract: As I retire from my long 43-year career as a PI researcher in Japan, I would like to give a short retrospective talk covering major topics of the field after the discovery of Josephson effect. I was involved with many of these topics. In the latter half of my talk, I will introduce our most recent progress in superconducting bosonic qubits. Utilizing superconducting Kerr parametric oscillators (KPOs), we successfully carried out X-gate and Z gate operations [1]. Moreover, the similar approach enables us to entangle a pair of Schrödinger’s cat states by two methods. The first involves the entanglement-preserving conversion between Bell states in the Fock-state basis and those in the cat-state basis. The second method implements a gate between two cat states following the procedure for Fock-state encoding. This simple and fast gate operation completes a universal quantum gate set in a KPO system [2]. We also implemented a three-photon KPO and explore its potential as a protected bosonic qutrit. We confirmed quantum coherence by demonstrating three-photon Rabi oscillations and performing direct Wigner function measurements that revealed the formation of three-component catlike states [3].

D. Iyama, et al. “Observation and manipulation of quantum interference in a superconducting Kerr parametric oscillator”. Nat Commun 15, 86 (2024).

Daisuke Hoshi, et al, “Entangling Schrödinger’s cat states by bridging discrete- and continuous-variable encoding”, Nature Communications 16, 1309 (2025)

Sangil Kwon, et al, “Realization of a Protected Cat-Qutrit Manifold via Engineered Quantum Tunnelling”, arXiv:2601.17675

The Göteborg Mesoscopic Lectures are sponsored by the Royal Swedish Academy of Sciences through its Nobel Institute of Physics. Further information by Per Delsing, Mats Jonson, or Tord Claeson. If you want to meet prof Tsai, please let TC know.