Multiqubit coherence of mixed states near event horizon

Abstract

We investigate the coherence of mixed Greenberger-Horne-Zeilinger (GHZ) and W states for bosonic and fermionic fields when a subset of $n$ ($n<N$) qubits experiences Hawking radiation near a Schwarzschild black hole. Analytical expressions are derived for the coherence of mixed N-qubit systems, including both the physically accessible and inaccessible parts in curved spacetime. The results show that the mixed W state maintains its coherence more effectively than the GHZ state as the Hawking temperature increases, even though its entanglement is weaker. As the number of qubits grows, W-state coherence becomes increasingly resistant to gravitational decoherence. Furthermore, fermionic fields preserve stronger entanglement, while bosonic fields retain higher coherence, highlighting a clear contrast between different particle statistics. These findings demonstrate how the Schwarzschild spacetime reshapes the balance between quantum coherence and entanglement, offering guidance for future relativistic quantum information applications.