Description
Reliable generation and control of quantum states with genuine quantum correlations,
particularly multipartite entangled states, are essential for quantum technologies, including
quantum information processing, quantum thermodynamics, and metrology. Yet unavoidable
dissipation can limit their fidelity and preparation speed. Non-Hermitian systems offer a
promising route to harness dissipation for quantum-state engineering, as their spectral
degeneracies, including exceptional points (EPs), provide new ways to control quantum
dynamics.
I will first discuss higher-order EPs in driven non-Hermitian superconducting qubits with local
dissipation and their role in multipartite entanglement generation [1]. In the vicinity of these EPs,
weak all-to-all and nearest-neighbor spin-exchange interactions enable rapid generation of GHZ
and W states, respectively [2, 3]. I will further discuss the robustness of these states against
variations in system size, coupling asymmetries, off-resonant driving, and quantum decoherence
[3].
I will next introduce non-Hermitian qubits coupled through collective dissipation, which
produces a hierarchy of decay rates separating rapidly decaying superradiant modes from long-
lived subradiant modes. We identify a degeneracy among collective subradiant modes that,
unlike an exceptional point, does not involve eigenvector coalescence [4]. Crossing this
degeneracy switches the slowest-decaying manifold between the symmetric Dicke mode and the
lowest-spin Dicke manifolds, while tuning the system toward or away from the degeneracy
controls the relaxation timescale toward the desired eigenmodes. We further investigate the role
of the initial state on the relaxation dynamics, and we uncover a counterintuitive phenomenon
known as the informational Mpemba effect, whereby more mixed initial states can reach the
asymptotic state faster than less mixed states [4]. These results demonstrate that quantum
dynamics across non-Hermitian degeneracies can provide new routes for quantum-state
engineering, and relaxation control in open quantum systems.
References
[1] M. Naghiloo et al., Nat. Phys. 15, 1232 (2019).
[2] C. G. Feyisa, J.-S. You, Huan-Yu Ku, and H. H. Jen, Quantum Sci. Technol. 10, 025021
(2025).
[3] C. G. Feyisa, C.-Y. Liu, M. S. Hasan, J. S. You, Huan-Yu Ku, and H. H. Jen, Phys. Rev.
Research 7, 033060 (2025).
[4] C. G. Feyisa, Huan-Yu Ku, J.-S. You, and H. H. Jen, arXiv:2604.07926 (2026).