Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea.
Proc Natl Acad Sci U S A. 2013 Jan 22;110(4):1227-31. doi: 10.1073/pnas.1206910110. Epub 2013 Jan 7.
Quantum-mechanical wave-particle duality implies that probability distributions for granular detection events exhibit wave-like interference. On the single-particle level, this leads to self-interference--e.g., on transit across a double slit--for photons as well as for large, massive particles, provided that no which-way information is available to any observer, even in principle. When more than one particle enters the game, their specific many-particle quantum features are manifested in correlation functions, provided the particles cannot be distinguished. We are used to believe that interference fades away monotonically with increasing distinguishability--in accord with available experimental evidence on the single- and on the many-particle level. Here, we demonstrate experimentally and theoretically that such monotonicity of the quantum-to-classical transition is the exception rather than the rule whenever more than two particles interfere. As the distinguishability of the particles is continuously increased, different numbers of particles effectively interfere, which leads to interference signals that are, in general, nonmonotonic functions of the distinguishability of the particles. This observation opens perspectives for the experimental characterization of many-particle coherence and sheds light on decoherence processes in many-particle systems.
量子力学的波粒二象性意味着，颗粒探测事件的概率分布表现出类似波的干涉。在单粒子水平上，这会导致光子以及大质量粒子的自干涉，例如在穿过双缝时，只要没有任何观察者能够获得任何方式的信息，即使原则上也不行。当超过一个粒子进入游戏时，它们的特定多粒子量子特征会在相关函数中表现出来，前提是粒子不能被区分。我们习惯于相信，随着可区分性的增加，干涉会单调地消失——这与单粒子和多粒子水平上的可用实验证据一致。在这里，我们通过实验和理论证明，只要有两个以上的粒子相互干涉，这种量子到经典的转变的单调性就是例外而不是规则。随着粒子可区分性的连续增加，不同数量的粒子实际上会相互干涉，这导致干涉信号通常是非单调函数的粒子可区分性。这一观察结果为多粒子相干性的实验表征开辟了前景，并揭示了多粒子系统中退相干过程的本质。
