Open systems, governed by non-Hermitian Hamiltonians, evolve fundamentally
differently from their Hermitian counterparts and facilitate many unusual
applications. Although non-Hermitian but parity-time (PT) symmetric
dynamics has been realized in a variety of classical or semiclassical systems,
its fully quantum-mechanical demonstration is still lacking. Here we
ingeniously engineer a highly controllable anti-Hermitian spin-boson model in a
circuit quantum-electrodynamical structure composed of a decaying artificial
atom (pseudospin) interacting with a bosonic mode stored in a microwave
resonator. Besides observing abrupt changes in the spin-boson entanglement
evolution and bifurcation transition in quantum Rabi splitting, we demonstrate
super-sensitive quantum sensing by mapping the observable of interest to a
hitherto unobserved PT-manifested entanglement evolution. These
results pave the way for exploring non-Hermitian entanglement dynamics and
PT-enhanced quantum sensing empowered by nonclassical correlations.Comment: 25 pages, 19 figure