<p>Non-Hermitian quantum theories with parity-time symmetry have been rapidly developed and hold great promise for future applications. Unlike most of the existing works that consider the symmetry of the free energy terms (e.g., gain–loss system), in this paper it is proved that a realizable non-Hermitian two-body interaction with asymmetric coupling strength between quantum resonance systems can also have a real spectrum after the exceptional point. Such a non-Hermitian interaction is realized in designed optomechanics, and we find that some nonlinear effects, such as synchronization phase transition and chaos, are observed as expected. Moreover, all quantum properties of the whole system, including the asymmetric interaction parts, can be solved by full quantum theory. Our results provide a platform for realizing parity-time symmetry devices and studying properties of non-Hermitian quantum mechanics.</p>