Department of Physics, Fuzhou University, Fuzhou 350116, China.
Department of Physics, Zhejiang University, Hangzhou 310027, China.
Phys Rev Lett. 2015 Dec 31;115(26):260403. doi: 10.1103/PhysRevLett.115.260403. Epub 2015 Dec 28.
A quantum system can behave as a wave or as a particle, depending on the experimental arrangement. When, for example, measuring a photon using a Mach-Zehnder interferometer, the photon acts as a wave if the second beam splitter is inserted, but as a particle if this beam splitter is omitted. The decision of whether or not to insert this beam splitter can be made after the photon has entered the interferometer, as in Wheeler's famous delayed-choice thought experiment. In recent quantum versions of this experiment, this decision is controlled by a quantum ancilla, while the beam splitter is itself still a classical object. Here, we propose and realize a variant of the quantum delayed-choice experiment. We configure a superconducting quantum circuit as a Ramsey interferometer, where the element that acts as the first beam splitter can be put in a quantum superposition of its active and inactive states, as verified by the negative values of its Wigner function. We show that this enables the wave and particle aspects of the system to be observed with a single setup, without involving an ancilla that is not itself a part of the interferometer. We also study the transition of this quantum beam splitter from a quantum to a classical object due to decoherence, as observed by monitoring the interferometer output.
一个量子系统可以表现为波或粒子，这取决于实验的安排。例如，当使用马赫-曾德尔干涉仪测量光子时，如果插入第二个分束器，那么光子表现为波，如果省略这个分束器，那么光子表现为粒子。这个分束器是否插入的决定可以在光子进入干涉仪之后做出，就像惠勒著名的延迟选择思维实验一样。在最近的量子版本的这个实验中，这个决定是由一个量子辅助物控制的，而分束器本身仍然是一个经典的物体。在这里，我们提出并实现了量子延迟选择实验的一个变体。我们将超导量子电路配置为拉姆齐干涉仪，其中作为第一分束器的元件可以处于其活跃和不活跃状态的量子叠加中，这可以通过其魏格纳函数的负值来验证。我们表明，这使得系统的波和粒子方面可以用单个设置来观察，而不涉及不是干涉仪一部分的辅助物。我们还研究了由于退相干导致这个量子分束器从量子到经典物体的转变，这可以通过监测干涉仪的输出来观察到。
