The interaction between light and matter is the foundation for how we percieve the world. Information about our surroundings reach our eyes in the form of photons, the fundamental unit of light, where it is transformed into electrical impulses that can be interpreted by our brain. However, to collect information is not the only utility of light, as it can also be emitted to affect objects around us. Specifically, by tailored laser pulses inducing electric currents and mechanical vibrations, it is possible to control material properties with great precision, and to make materials magnetic or electrically conducting.
One problem with laser light is that the material is easily heated, and that the induced properties only survive for a short time after the pulse has passed. This makes laser light best suited to control electrically insulating materials, which are not as easily heated as conducting materials. It is also best adapted to “classical” states, which are states that are well described by classical statistical physics, and where quantum mechanical coherence (i.e. that particles move in a coordinated as opposed to independent fashion) plays a minor role. Since laser driving is not well adapted to manipulating quantum mechanical states, it is of great importance to find new and alternative ways to optically control such states. This could enable the development of more fault-tolerant components for quantum computing, which are predicted to be able to solve certain problems (in particular complex scientific problems involving quantum mechanics) more efficiently than ordinary computers.
In this project, I have developed methods where optical cavities are used to stabilize quantum mechanical states in materials embedded in the cavity. An optical cavity is like a small container for light, and consists in the simplest case of two parallel (high quality) mirrors. Because of quantum mechanical effects, the space between the mirrors is never empty, but filled with constant fluctuations of the electromagnetic field. By carefully designing the cavity, e.g. by varying its geometry and the constituent materials, it is possible to control the fluctuations of the field. As a material can sense the changes in the electromagnetic fluctuations, and adapt its properties in response to it, cavities can be used to control the embedded material. The key difference with laser based methods is that the cavity does not need to contain “real” photons, but will remain in its quantum mechanical ground state. The change in the material is thereby a purely quantum mechanical effect, in the sense that classical physics would describe the cavity as empty, and its effect on the material as none.
