标题： 量子延迟选择实验中分束器处于量子叠加态 显示英文标题

标题： Quantum delayed-choice experiment with a beam splitter in a quantum superposition

摘要： 量子系统可以根据实验安排表现出波或粒子的行为。 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，光子表现为波；如果省略该分束器，则表现为粒子。 是否插入该分束器的决定可以在光子进入干涉仪之后做出，如惠勒著名的延迟选择思想实验所示。 在最近的该实验的量子版本中，这一决定由一个量子辅助系统控制，而分束器本身仍然是一个经典物体。 在这里，我们提出并实现了一个量子延迟选择实验的变种。 我们将超导量子电路配置为拉姆齐干涉仪，其中作为第一个分束器的元件可以处于其激活和非激活状态的量子叠加态，这通过其威格纳函数的负值得到了验证。 我们表明，这使得系统波和粒子特性能够在单一设置中被观察到，而无需涉及一个本身不属于干涉仪的辅助系统。 我们还研究了由于退相干，该量子分束器从量子物体转变为经典物体的过渡过程，这是通过监测干涉仪输出来观察的。 显示英文摘要

摘要： 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.