A common wisdom in quantum mechanics is that the Hamiltonian has to be Hermitian in order to ensure a real eigenvalue spectrum. Yet, parity–time (PT)-symmetric Hamiltonians are sufficient for real eigenvalues and therefore constitute a complex extension of quantum mechanics beyond the constraints of Hermiticity. However, as only single-particle or classical wave physics has been exploited so far, an experimental demonstration of the true quantum nature of PT symmetry has been elusive. In our work, we demonstrate two-particle quantum interference in a PT-symmetric system. We employ integrated photonic waveguides to reveal that the quantum dynamics of indistinguishable photons shows strongly counterintuitive features. To substantiate our experimental data, we analytically solve the quantum master equation using Lie algebra methods. The ideas and results presented here pave the way for non-local PT-symmetric quantum mechanics as a novel building block for future quantum devices.

量子力学中的一个常识是，哈密顿量必须是埃尔米特量，以确保真实的特征值谱。但是，奇偶时间（PT）对称的哈密顿量对于真实的特征值就足够了，因此构成了量子力学的复杂扩展，超出了Hermiticity的限制。但是，由于到目前为止仅利用了单粒子或经典波物理学，因此无法获得PT对称性的真正量子性质的实验证明。在我们的工作中，我们演示了PT对称系统中的两粒子量子干涉。我们采用集成的光子波导来揭示不可区分的光子的量子动力学表现出强烈的反直觉特征。为了证实我们的实验数据，我们使用李代数方法解析地解决了量子主方程。