Ancilla-assisted nondestructive discrimination of distributed GHZ-class states
Nondestructive quantum state discrimination is a fundamental primitive in distributed quantum information processing, where shared multipartite entangled resources need to be identified without being consumed. In this work, we present a scalable ancilla-assisted protocol for the strict nondestructive discrimination of $n$-qubit GHZ-class states distributed among distant parties. By employing multipartite GHZ ancillary states and local unitary interactions, we show that the computational-pattern and relative-phase information of the system GHZ state can be coherently mapped onto two ancillary registers while leaving the system state unchanged. We explicitly derive the discrimination rules for three- and four-qubit GHZ-class states and develop a systematic extension to arbitrary $n$. We further investigate the discrimination protocol in the presence of depolarizing and amplitude-damping noise in the ancillary system and obtain analytical expressions for the success probability and the corresponding critical noise thresholds. The protocol is also implemented using the IBM Qiskit platform to demonstrate its experimental feasibility and reproduce the expected ancillary measurement signatures. The proposed framework provides a scalable approach to the strict nondestructive discrimination of multipartite GHZ-class states and suggests a broader interpretation of the ancillary GHZ resources as probes of decoherence, opening a possible connection to quantum decoherence sensing in distributed quantum systems.