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

TL;DR

This paper demonstrates a hybrid discrete-continuous variable approach to entangle Schr"odinger's cat states using superconducting Kerr parametric oscillators, enabling universal quantum gates and advancing multi-qubit quantum platforms.

Contribution

It introduces a novel DV-CV hybrid method to entangle cat states and implement universal gates in KPO systems, bridging two quantum encoding paradigms.

Findings

Successfully entangled Schr"odinger's cat states using two methods.

Implemented a $ oot i$SWAP gate for cat states, enabling universal quantum operations.

Marked a step toward multi-qubit quantum computing with KPO systems.

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.