Rydberg States in Lanthanoid Atoms for Quantum Simulation

This project aims to explore the properties of highly excited electronic states in erbium atoms and their prospects for quantum simulation. Erbium atoms have a very complex structure, with several active outer electrons which can be manipulated with light fields. We will investigate so-called Rydberg states, where one of the electrons is in a highly excited state. In these extreme conditions, the negative charge of the electron can be shifted easily with respect to the positive charge of the core, which results in a large electric dipole and causes an extremely strong and long-range interaction between these atoms. However, the properties of Rydberg states in erbium are only little explored so far. The proposed project will study their properties with high precision to determine their life time, their response to laser light of different colours, and the interactions between the atoms. Rydberg states have been studied intensively in atoms where only one electron is available but after exciting this electron, the remaining atomic core is blind and reacts only very weakly on light fields. This limits the possibilities to apply usual techniques to control the atoms via laser fields. In erbium, though, if one of the electrons is excited to a Rydberg state, there are still several electrons that strongly react on laser fields. Thus we want to explore the possibilities to (i) trap, (ii) cool, and (iii) detect the atoms, both in their ground state, as well as for the first time, in their Rydberg state. To (i) trap the atoms, we will use an array of strongly focussed light beams, so-called optical tweezers, to pin the atoms in a controlled pattern. We will try (ii) cooling schemes by shining light onto the atoms in special configurations. This allows us to reach extremely low temperatures just a fraction of a degree above the absolute zero temperature of -273C. By collecting light that is scattered by the atoms and imaging it with a camera, we will try to (iii) detect the atoms and determine their internal state and their properties. While such techniques are well-known for ground-state atoms, the application to Rydberg states is completely new and unexplored. The extremely strong interaction bring about very fast dynamics of the system, and thus Rydberg states in erbium are promising candidates for the construction of a quantum simulator. This is a device that helps physicists understand complex properties of a physical systems that cannot be calculated with classical computers. The unintuitive properties of quantum physics can be exploited to make a calculation much more efficient and thus solve problems that would require immense times for calculation even on the strongest classical computers.

Quantum simulators are some of the most faszinating recent research topics, and first models are aleardy available compercially. Different platforms strive to demonstrate the first prototype to be universally superior to classic computers. One of the most promising platforms are arrays of single neutral atoms which are trapped in optical tweezers and brought into highly excited states via laser beams. Thise so-called Rydberg states show extremely strong, controllable, interactions, which is the foundation for quantum simulation. In the course of the Lise Meitner project M 2683, series of Rydberg states in erbium have been investigated for the first time with a high resolution. These highly complex atoms are distinct from frequently utilized alkali or akaline earth atoms in the large number of electrons contributing to the optical properties. Thise contributions make the properties complicated, but also very rich in new possibilities for trapping and exciting these atoms. For the investigation of the Rydberg series we used a method of electromagnetically induced transparency, where quantum interference on an atomic beam is used to characterize the corresponding states, without the need of complex detection schemes. In the specially constructed chamber, we are able to control magnetic fields and thus study the magnetic properties of these states, and also determine their total angular momentum. Future work on this experimental apparatus, based on the work and planning done in this project, will decelerate the atoms, trap them, and arrange them in optical tweezers, to study their aptitude for quantum simulation in detail.