  Quantum correlations, both spatial and temporal, are the central pillars of
quantum mechanics. Over the last two decades, a big breakthrough in quantum
physics is its complex extension to the non-Hermitian realm, and dizzying
varieties of novel phenomena and applications beyond the Hermitian framework
have been uncovered. However, unique features of non-Hermitian quantum
correlations, especially in the time domain, still remain to be explored. Here,
for the first time, we experimentally achieve this goal by using a parity-time
(PT )-symmetric trapped-ion system. The upper limit of temporal quantum
correlations, known as the algebraic bound, which has so far not been achieved
in the standard measurement scenario, is reached here by approaching the
exceptional point (EP), thus showing the unexpected ability of EPs in tuning
temporal quantum correlation effects. Our study, unveiling the fundamental
interplay of non-Hermiticity, nonlinearity, and temporal quantum correlations,
provides the first step towards exploring and utilizing various non-Hermitian
temporal quantum effects by operating a wide range of EP devices, which are
important for both fundamental studies and applications of quantum EP systems.
