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arXiv · 2604.20680

Controllable non-Hermitian topology in a dynamically protected cat qubit

Tian-Le Yang·Pei-Rong Han·Zhen-Biao Yang·Shi-Biao Zheng
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Abstract

Dissipatively stabilized cat qubits are promising for fault-tolerant quantum information processing, yet their non-Hermitian (NH) spectral topology remains largely unexplored. We uncover rich Liouvillian exceptional structures in a cat-qubit mode stabilized by two-photon drive (TPD) and engineered two-photon loss, in the presence of single-photon drive (SPD) and single-photon loss. In the parameter space spanned by SPD strength and detuning, we identify both second- and third-order Liouvillian exceptional points (LEP2s and LEP3s). Remarkably, we show that the phase $\theta$ of TPD provides coherent control over these exceptional points: the LEP3 diverges and vanishes at $\theta=\pi/2$, while remaining stable and tunable elsewhere. We introduce a topological invariant based on the winding number of a resultant vector, which robustly identifies LEP3s with unit topological charge. Full master-equation simulations confirm that the system dynamics remains confined to the logical subspace with near-unity fidelity. Our results bridge dissipative stabilization, phase-coherent control, and NH topology, demonstrating controllable higher-order LEPs in open quantum systems.

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Tian-Le Yang, Pei-Rong Han, Zhen-Biao Yang, Shi-Biao Zheng. 2026-04-22. Controllable non-Hermitian topology in a dynamically protected cat qubit. https://arxiv.org/abs/2604.20680

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