Researchers guide a single ion through a Bose-Einstein condensate

研究人员引导单个离子通过Bose-Einstein冷凝物

by University of Stuttgart

斯图加特大学

The path of the positively charged ion (yellow) through the BEC (green) can still only be depicted artistically. An ion microscope currently being developed at the Fifth Institute of Physics at the University of Stuttgart will make this path directly visible with a resolution of less than 200 nanometers. Credit: University of Stuttgart/PI5, Celina Brandes 

带正电的离子（黄色）通过BEC（绿色）的路径仍然只能用艺术的方式描绘。斯图加特大学第五物理研究所目前正在研制的离子显微镜将使这条路径直接可见，分辨率不到200纳米。学分：斯图加特大学/PI5，Celina Brandes

Transport processes are ubiquitous in nature, but still raise many questions. The research team around Florian Meinert from the Fifth Institute of Physics at the University of Stuttgart has now developed a new method to observe a single charged particle on its path through a dense cloud of ultracold atoms. The results were published in Physical Review Letters and are further reported in a Viewpoint column in the journal Physics.

运输过程本质上无处不在，但仍然引发许多问题。斯图加特大学第五物理研究所的弗洛里安·迈纳特（Florian Meinert）周围的研究小组现在已经开发出一种新方法，可以在通过超冷原子的密集云的路径上观察单个带电粒子。结果发表在《 Physical Review Letters》上，并在《 Physics》杂志的“观点”专栏中进一步报道。

Meinert's team used a Bose-Einstein condensate (BEC) for their experiments. This exotic state of matter consists of a dense cloud of ultracold atoms. By means of sophisticated laser excitation, the researchers created a single Rydberg atom within the gas. In this giant atom, the electron is a thousand times further away from the nucleus than in the ground state and thus only very weakly bound to the core. With a specially designed sequence of electric field pulses, the researchers snatched the electron away from the atom. The formerly neutral atom turned into a positively charged ion that remained nearly at rest despite the process of detaching the electron.

Meinert的团队在实验中使用了Bose-Einstein冷凝物（BEC）。这种奇特的物质状态由超冷原子的密集云组成。通过复杂的激光激发，研究人员在气体中产生了一个里德堡原子。在这个巨大的原子中，电子离原子核的距离比基态更远，因此与核的结合非常弱。通过特殊设计的电场脉冲序列，研究人员将电子从原子上夺走了。原先的中性原子变成带正电的离子，尽管有分离电子的过程，但几乎保持静止。

In the next step, the researchers used precise electric fields to pull the ion in a controlled way through the dense cloud of atoms in the BEC. The ion picked up speed in the electric field, collided on its way with other atoms, slowed down and was accelerated again by the electric field. The interplay between acceleration and deceleration by collisions led to a constant motion of the ion through the BEC.

下一步，研究人员使用精确的电场以受控方式将离子拉过BEC中密集的原子云。离子在电场中的吸收速度加快，在与其他原子碰撞的过程中减慢了速度，并再次被电场加速。碰撞引起的加速和减速之间的相互作用导致离子通过BEC不断运动。

"This new approach allows us to measure the mobility of a single ion in a Bose-Einstein condensate for the very first time," says Thomas Dieterle, a Ph.D. student who participated in the experiment. The researchers' next goal is to observe collisions between a single ion and atoms at even lower temperatures, where quantum mechanics instead of classical mechanics dictates the processes. "In the future, our newly created model system—the transport of a single ion—will allow for a better understanding of more complex transport processes that are relevant in many-body systems, e.g., in certain solids or in superconductors," Meinert says. These measurements are also an important step on the way to investigate exotic quasi-particles, so-called polarons, which can arise through interaction between atoms and ions.

“这种新方法使我们能够首次测量玻色-爱因斯坦凝聚物中的单个离子的迁移率，”博士托马斯·迪特勒（Thomas Dieterle）说。参加实验的学生。研究人员的下一个目标是在甚至更低的温度下观察单个离子与原子之间的碰撞，其中量子力学而非经典力学决定了该过程。 Meinert说：“将来，我们新创建的模型系统-单个离子的传输-将使人们更好地理解与多体系统（例如某些固体或超导体）相关的更复杂的传输过程。” 。这些测量也是研究奇特的准粒子（所谓的极化子）的重要步骤，这些粒子可能通过原子和离子之间的相互作用而产生。

The neighboring lab at the institute is already working on an ion microscope that will allow researchers to observe collisions between atoms and ions directly. While an electron microscope uses negatively charged particles to create an image, this is what happens in an ion microscope with positively charged ions. Electrostatic lenses deflect ions similar to light rays in a classical optical microscope.

该研究所附近的实验室已经在研究离子显微镜，这将使研究人员可以直接观察原子和离子之间的碰撞。电子显微镜使用带负电的粒子来产生图像，而带正电离子的离子显微镜就是这种情况。静电透镜使离子偏转，类似于经典光学显微镜中的光线。

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 来源于：phys