Robustness of tripartite entangled states in passive PT-symmetric qubits

Abstract: Non-Hermitian quantum systems have attracted significant interest in recent years due to the presence of unique spectral singularities known as exceptional points (EPs), where eigenvalues and eigenvectors coalesce. The drastic changes in these systems around their EPs have led to unique entanglement dynamics, which remained elusive until quite recently. In this work, we theoretically investigate the robustness of tripartite entanglement induced by EPs of the passive PT-symmetric non-Hermitian superconducting qubits, both in stand-alone configurations and hybrid setups with Hermitian qubits. In particular, we consider the qubits with both all-to-all and nearest-neighbour couplings under uniform and non-uniform coupling strengths. Our results reveal that non-Hermitian qubits with all-to-all coupling generate GHZ states, while those with nearest-neighbour interactions produce W states. These entangled states are resilient to non-uniform couplings and off-resonant driving fields. Moreover, the hybrid configurations combining Hermitian and non-Hermitian qubits suggest the importance of EPs for generating and maintaining genuine tripartite entanglement in our system. Additionally, driving the PT-symmetric qubits with a strong Rabi frequency can help sustain tripartite entanglement over time by countering losses, while strong inter-qubit coupling can benefit these entangled states in the low dissipation regime. These findings suggest that exploiting non-Hermitian systems and their associated EPs can create robust entangled states which are useful for both fundamental studies and quantum technologies.