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arXiv · 2406.17999

Entangling Schr\"odinger's cat states by bridging discrete- and continuous-variable encoding

Daisuke Hoshi·Toshiaki Nagase·Sangil Kwon·Daisuke Iyama·Takahiko Kamiya·Shiori Fujii·Hiroto Mukai·Shahnawaz Ahmed·Anton Frisk Kockum·Shohei Watabe·Fumiki Yoshihara·Jaw-Shen Tsai
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Abstract

In quantum information processing, two primary research directions have emerged: one based on discrete variables (DV) and the other on the structure of quantum states in a continuous-variable (CV) space. Integrating these two approaches could unlock new potentials, overcoming their respective limitations. Here, we show that such a DV-CV hybrid approach, applied to superconducting Kerr parametric oscillators (KPOs), enables us to entangle a pair of Schr\"odinger's cat states by two methods. The first involves the entanglement-preserving conversion between Bell states in the Fock-state basis (DV encoding) and those in the cat-state basis (CV encoding). The second method implements a $\sqrt{\textrm{iSWAP}}$ 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. Our work offers powerful applications of DV-CV hybridization and marks a first step toward developing a multi-qubit platform based on planar KPO systems.

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Daisuke Hoshi, Toshiaki Nagase, Sangil Kwon, Daisuke Iyama, Takahiko Kamiya, Shiori Fujii, Hiroto Mukai, Shahnawaz Ahmed, Anton Frisk Kockum, Shohei Watabe, Fumiki Yoshihara, Jaw-Shen Tsai. 2024-06-26. Entangling Schr\"odinger's cat states by bridging discrete- and continuous-variable encoding. https://doi.org/10.1038/s41467-025-56503-8

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