Quantum technologies are a recent hot topic in the EU and worldwide. The control of matter on the quantum level offers completely new perspectives for computation, communication and simulation. One of those simulation tasks is chemistry, since quantum physics plays a crucial role in chemical reactions and molecular dynamics, which are relevant for many new developments, ranging from new fuel to new pharma. Those are problems which can quickly become very complex when simulated on classical computers. Recent methods in experimental quantum physics allow to cool matter particles, such as atoms or molecules, to very low temperatures, where quantum effects can be studied in a very clean and isolated environment. By methods of laser cooling, the particles are slowed down by orders of magnitude compared to their motion at room temperature, taking away almost their entire kinetic energy. This opened up the new field of ultracold chemistry, where precision studies of chemical reactions between those particles became possible. Now, their reaction or collision energies can be very precisely controlled, e.g. by laser light, which fuses together two or more atoms, forming a molecule (so-called photoassociation). Those molecules are usually not stable, as they will quickly decay into states of lower energy by releasing the excess energy as a photon (spontaneous emission). This process is, however, not well controlled - the molecules can randomly end up in one of many possible quantum states. Here, our project sets in: We want to control spontaneous emission to strongly enhance the production of a desired final quantum state. For this, we make use of an optical cavity, which is placed around the atoms/molecules and which strongly modifies the electromagnetic environment of the particles. By this, certain photon energies in the spontaneous emission process can be preferred, and it will be possible to produce an almost pure sample of cold molecules in a certain state, which would be an important starting point for further studies in ultracold chemistry. At the same time, we will observe the emitted photons with high efficiency, giving real-time insight into reaction dynamics (Objective 1). Furthermore, the detection of single particles in their quantum states, without destroying them, is another very important quantum technology. In this project, we want to make use of the cavity to detect single cold molecules. The presence of a molecule in a certain quantum state inside the cavity will modify the optical properties of the cavity, such as transmission, which can be measured (Objective 2).
