Colloquium: Dr. Hikaru Tamura | Institute for Molecular Science, National Institutes of Natural Science

ABSTRACT: Collecting many elements often gives rise to fascinating emergent phenomena that cannot be predicted from the individual elements. Understanding and controlling collective many-body phenomena potentially leads to the discovery of new properties and functionalities and advancing technologies. My research explores quantum collective phenomena in pristine systems made of ultracold atoms cooled to nano-Kelvin scale temperatures or interacting atoms and photons, utilizing a developed toolbox involving arbitrary potential shaping and tunable interactions.

In this talk, I will present two unique approaches for the detailed study of intricate collective phenomena. The first approach employs quantum gases confined in an optical box, leading to a homogeneous bulk density and sharp boundaries. I will explain how instabilities trigger the spontaneous emergence of self-patterned macroscopic structures from the uniform environment, including previously unseen vortex dipole necklaces and density crystals. This could pave the way for studying connections from quantum fluctuations—primarily the seeds of those instabilities—to quasiparticle excitations and large-scale structures. The second approach combines an array of individual atoms with a shared photonic channel. We demonstrate that microscopically

controlling atoms enables new ways to manipulate collectively scattered photons. Moreover, by overcoming long-standing challenges, we present, for the first time, trapped atoms integrated with a two-dimensional nanophotonic circuit, revealing atom-light superradiant cooperative coupling. This signifies the start of a new research field that merges the cold-atom toolbox with the rich functionalities of nanophotonic circuits.