The photon-like propagation of the Dirac electrons in graphene, together with its record-high electronic mobility^1,2,3, can lead to applications based on ultrafast electronic response and low dissipation^4,5,6. However, the chiral nature of the charge carriers that is responsible for the high mobility also makes it difficult to control their motion and prevents electronic switching. Here, we show how to manipulate the charge carriers by using a circular p–n junction whose size can be continuously tuned from the nanometre to the micrometre scale^7,8. The junction size is controlled with a dual-gate device consisting of a planar back gate and a point-like top gate made by decorating a scanning tunnelling microscope tip with a gold nanowire. The nanometre-scale junction is defined by a deep potential well created by the tip-induced charge. It traps the Dirac electrons in quantum-confined states, which are the graphene equivalent of the atomic collapse states (ACSs) predicted to occur at supercritically charged nuclei^{9,10,11,12,13}. As the junction size increases, the transition to the optical regime is signalled by the emergence of whispering-gallery modes^14,15,16, similar to those observed at the perimeter of acoustic or optical resonators, and by the appearance of a Fabry–Pérot interference pattern^17,18,19,20 for junctions close to a boundary.

狄拉克电子在石墨烯中的光子状传播及其创纪录的高电子迁移率^1,2,3，可导致基于超快电子响应和低耗散的^{4,5,6的应用}。然而，负责高迁移率的电荷载流子的手性也使得难以控制其运动并阻止电子开关。在这里，我们展示了如何通过使用圆形的p–n结来操纵电荷载流子，该结的大小可以连续地从纳米级调整到微米级^7,8。结的大小由双栅极器件控制，该器件由平面背栅极和点状顶栅极组成，该栅极是通过用金纳米线装饰扫描隧道显微镜尖端而制成的。纳米级结由尖端诱导的电荷产生的深势阱定义。它以量子约束态捕获狄拉克电子，量子约束态是石墨烯的原子塌陷态（ACSs）的等效物，原子塌陷态预计会在超临界带电核^{9,10,11,12,13发生}。随着结点尺寸的增加，耳语画廊模式^14,15,16的出现标志着向光学状态的过渡，类似于在声学或光学谐振器周边观察到的，以及法布里-佩罗特的出现干涉图样^17,18,19,20 用于靠近边界的路口。