We introduce Quantum Spectral Authentication (QSA), a primitive for verifying that a remote quantum endpoint still possesses a previously installed secret quantum resource, such as a hidden state or state-preparation capability, without revealing that secret. QSA uses fresh public unitary challenges and spectral features of the planted state to derive transcript-bound session material for explicit authentication. We analyse attack strategies including eigenstate propagation across challenges, repeated-session leakage, and direct online forgery. For practical implementation, we develop a symmetric verifier-driven unitary compiler compatible with low-depth quantum phase estimation. Simulations indicate that this symmetric fast-power construction is substantially more noise tolerant than an asymmetric alternative, and small-instance experiments on IBM ibm_fez provide a hardware sanity check. QSA therefore offers a plausible near-term authentication layer for quantum networks and control-plane applications.
@article{arxiv.2603.24868,
title = {Quantum Spectral Authentication under Public Unitary Challenges},
author = {S. P. Kish and H. J. Vallury and J. Pieprzyk and C. Thapa and S. Camtepe},
journal= {arXiv preprint arXiv:2603.24868},
year = {2026}
}