Renewal: Fundamental Physics of Polariton Condensates

非技术描述：该项目由凝聚态物理和原子、分子和光学物理-实验计划联合资助，支持新一类超流体的基础物理研究。超流是一种本质上的量子现象，在一定的温度以下，许多粒子自发地结合在一起，形成波。只有为数不多的几个物理系统是这样运作的。最古老的是超流液氦，它的流动粘度为零。超导金属是另一个例子，其中电子作为波，以零电阻流动，超冷原子在超高真空中，由激光和磁场稳定。在过去的十年里，另一类超流体受到了广泛的关注，即被称为“极化子”的“重光子”，其中的光子可以像液体一样流动。该项目支持对这些极化子超流体的基础研究，这些超流体是通过使用作为该项目的一部分制造的半导体结构实现的，就流畅性和缺乏杂质而言，这些结构是世界上最好的。这个项目可以对增加我们对超流体普遍性质的理解，以及使新型光通信设备成为可能产生广泛的影响。该项目的PI还将继续与匹兹堡的卡内基科学中心合作，对公众进行一般量子力学和光学主题的教育。技术描述：该项目支持Pi Snoke继续研究GaAsAlGaAs微腔中激子-偏振子的基本性质。这些结构由Snoke小组设计，然后由普林斯顿的Loren Pfeiffer小组和滑铁卢大学的ZBig Wasilewski两个实验室使用分子束外延制造。该项目的一个目标是提高这些微腔结构的质量，特别是制造具有高度平坦度和非常少的结构外光泄漏的大面积结构，这将允许在传播长度为数百微米的芯片上实现光学电路。斯诺克团队将使用包括皮秒时间分辨光谱、成像和干涉测量在内的先进光学方法来研究这些结构中的极化子超流体。在过去的一年里，已经取得了两个突破性的结果，近期的目标将是进行后续实验，以充分了解这些影响。其中之一是演示了环中极化子超流体的真正持续电流。虽然在其他系统中已经看到了持续电流的间接证据，但微腔极化系统允许在循环中直接、原位测量超流体的相。另一个新的结果是，当系统处于热平衡状态时，可以高精度地测量超流分数。观察到了一个普遍的幂定律，这是理论上没有预测到的，也没有在其他实验系统中观察到。与多体理论家正在进行的合作将寻求为这一幂定律创建一个分析模型。从长远来看，该项目将寻求建立耦合极化子超流体网络，既可用于超高速(~10ps)光交换方法，也可用于模拟光计算的新方法，以解决传统计算机难以解决的数学问题。该奖项反映了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。

Nontechnical decription:This project, funded jointly by the Condensed Matter Physics and Atomic, Molecular and Optical Physics - Experiment programs, supports fundamental physics studies in a new class of superfluids. Superfluidity is an intrinsically quantum phenomenon in which below a certain temperature, many particles spontaneously join together to act as a wave. There are just a few physical systems that are known to act this way. The oldest is superfluid liquid helium, which flows with zero viscosity. Superconducting metals are another example, in which electrons act as a wave, and flow with zero resistance, and ultracold atoms in ultrahigh vacuum, stabilized by laser beams and magnetic field are another. In the past decade, another class of superfluid has received widespread attention, namely “heavy photons” known as “polaritons,” in which photons can flow like a liquid. This project supports basic research studies of these polariton superfluids, made possible by using semiconductor structures, fabricated as part of this project, that are the best in the world in terms of smoothness and lack of impurities. This project can have broad impact in increasing our understanding of universal properties of superfluids, and in making possible new types of optical communications devices. The PI of the project will also continue to collaborate with the Carnegie Science Center in Pittsburgh to educate the public on general quantum mechanics and optics topics.Technical description: This project supports the continuing work of PI Snoke on fundamental properties of exciton-polaritons in GaAs-AlGaAs microcavities. The structures are designed by the Snoke group and then fabricated using molecular-beam epitaxy by two labs, the group of Loren Pfeiffer at Princeton and the group of Zbig Wasilewski at the University of Waterloo. One goal of the project is to advance the quality of these microcavity structures, in particular to make large area structures with a high degree of flatness and very little leakage of light out of the structures, which will allow the possibility of optical circuits on a chip with propagation lengths of hundreds of microns. The Snoke group will use advanced optical methods including picosecond time-resolved spectroscopy, imaging, and interferometry to study polariton superfluids in these structures. In the past year, two breakthrough results have been obtained, and an immediate goal will be to perform followup experiments to fully understand these effects. One of these is the demonstration of a true persistent current of a polariton superfluid in a ring. While indirect evidence for persistent current has been seen in other systems, the microcavity polariton system allows direct, in situ measurement of the phase of the superfluid while it is circulating. The other new result is a highly accurate measurement of the superfluid fraction while the system is in thermal equilibrium. A universal power law has been observed which was not theoretically predicted nor observed in other experimental systems. Ongoing collaboration with many-body theorists will seek to create an analytical model for this power law. In the longer term, this project will seek to make networks of coupled polariton superfluids, which can be used both for ultrafast (~10 ps) optical switching methods as well as novel methods of analog optical computing to solve mathematical problems that are hard for traditional computers.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.