Spatial Coherence of Light in Collective Spontaneous Emission

激光发明于1960年，给许多科学学科带来了革命性的变化，并对社会产生了巨大的影响。例如，目前所有的长途通信，包括互联网上的数据传输，都是使用通过光纤(细玻璃电缆)传输信息的激光完成的。激光的许多显著特性依赖于它在空间上是相干的；也就是说，激光是由以可预测的方式移动的平滑而连续的电磁波组成的。激光器的这一特性使其明显有别于灯和灯泡等其他光源。在这个项目中，研究小组将研究一种产生光的新方法，这种方法具有这种显著的相干特性，但依赖于与激光截然不同的操作原理。该团队将使用一组被冷却到低至10微开尔文的Rb原子。有了这个超冷的集合，该团队将研究从该集合发出的光具有这种相干特性的条件。这些实验是小规模的桌面实验，将由一群研究生和本科生领导，他们将在量子科学的前沿接受培训，学习在光学和量子计算中广泛应用的实验技术。该项目的成果将通过威斯康星州科学节和威斯康星州-麦迪逊大学科学考察等公共宣传活动传播。创造相干光的新方法依赖于一种被称为集体自发辐射的物理效应：当一组被激发的原子集体衰变到它们的基态时。当量子系统进入激发态时，它将通过一个称为自发辐射的过程衰变回基态。一般认为，来自不同发射体的自发辐射是作为无关事件发生的，并且不是相干的；要产生相干光，需要布居反转和受激发射。然而，Pi的团队最近在实验中证明了集体自发辐射中光的空间相干性；也就是说，由于原子与光的集体耦合，系综中不同位置的单个原子之间的发射变得相关(相位相干)。国际和平研究所的小组将调查和进一步探索这一结果在原子、分子和光学物理的许多相互关联的领域的影响。更具体地说，PIS团队将研究：(1)大样本、强激发区域中集体自发辐射中发射的光子的量子力学统计，(2)在相同区域内系统的时空量子动力学，以洞察超辐射和亚辐射模式的空间结构，以及(3)超辐射到亚辐射的转变，以及仅有亚辐射的集体衰变。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The laser, which was invented in 1960, has revolutionized many scientific disciplines and has had a large impact on society. For example, currently, all long-distance communication, including data transfer over the internet, is done using lasers carrying information through optical fibers (thin glass cables). Many remarkable properties of the laser rely on the fact that it is spatially coherent; that is the laser light is made up from a smooth and continuous electromagnetic wave that moves in a predictable way. This property of the laser clearly distinguishes it from other light sources such as lamps and light bulbs. In this project, the research team will investigate a new approach to produce light that has this remarkable coherence property, but instead relies on operational principles that are distinctly different from a laser. The team will use an ensemble of rubidium atoms that are cooled to temperatures that are as low as ten microkelvin. With this ultracold ensemble, the team will investigate the conditions under which the emitted light from the ensemble has this coherence property. The experiments are small-scale table-top experiments, and they will be led by a group of graduate and undergraduate students, who will be trained at the frontiers of quantum science and learn experimental techniques that are widely applicable in optics and quantum computing. The results of the project will be disseminated through public outreach efforts such as Wisconsin Science Festival and UW-Madison Science Expeditions. The new approach for creating coherent light relies on a physical effect referred to as collective spontaneous emission: when an ensemble of excited atoms decay to their ground state collectively. When a quantum system is put into an excited state, it will decay back to the ground state through a process termed spontaneous emission. It is generally assumed that the spontaneous emission from different individual emitters occurs as unrelated events and would not be coherent; to produce coherent light one would need population inversion and stimulated emission. However, the PI’s group has recently experimentally demonstrated spatial coherence of light in collective spontaneous emission; that is, emission between individual atoms at different locations in the ensemble become correlated (phase-coherent) due to collective coupling of the atoms to light. The PI’s group will investigate and further explore the implications of this result in many interrelated areas of atomic, molecular, and optical physics. More specifically, the PIs team will study: (1) the quantum mechanical statistics of the emitted photons in collective spontaneous emission in the large sample, strong excitation regime, (2) the spatio-temporal quantum dynamics of the system in this same regime to gain insight into the spatial structures of superradiant and subradiant modes, and (3) the superradiance-to-subradiance transition, as well as subradiance-only collective decay.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.