Our group’s expertise is the interplay between quantum materials and quantum light. This timely topic has important implications for the realization of futuristic quantum technologies, including quantum sensors, quantum communications and, on the longer run, quantum computers.

Our research develops from a fundamental principle of quantum mechanics, the particle-wave duality. This principle dictates that quantum particles can be simultaneously in different places (i.e. behave like a wave), and that quantum waves have a discrete nature (i.e. behave like particles). Over the last century, physicists have learned to deal with the counter-intuitive consequences of this principle. The research question that we investigate is what happens when both ingredients meet in a small region of space: How can we describe such a “soup” of particles and waves?

Our main achievements deal with the fundamental blocks of quantum materials (electrons), quantum light (photons), and their interactions.

  • Electrons are responsible for the flow of electricity in materials. At low temperatures, they can behave like a wave and stretch across long wires. This phenomenon gives rise to materials that can carry electricity perfectly, without losses. These materials are known as superconductors, and rely on the fact that electrons can behave as waves. In our research we were able to visualize the shape of the wave of the electrons (their Wannier function) in a superconductor. These findings pave the way to understand what makes these materials superconducting, and to engineer smarter materials.
  • Photons are particles that carry a small unit of light. Under normal conditions, photons do not interact with each other. This is why several people can look at the same screen without interfering with each other. Recent experiments demonstrated that if photons are trapped in a box (an “optical cavity”) that is densely filled with atoms, they begin to interact. In our research, we described one important consequence of these interactions: The photons behave as classical particles and redistribute the energy among themselves, following the Boltzmann equipartition principle. This is an extreme consequence of the particle-wave duality. Our findings can help build light sources that are programmable and more efficient.
  • Topology is a branch of mathematics, which has been recently discovered to have important consequences in Physics (see the 2016 Nobel Prize in Physics). The key idea of topology is that some information can be hidden from local observers, and is rather encoded in non-local variables. In material science, this means that two materials can appear identical to any local probe, although their intrinsic nature is radically different. In our research, we proposed an experiment to observe directly a non-local order in systems of interacting atoms and photons. The experiment was performed at the Max Plank Institute in Munich (Germany), and offered the first direct observation of a non-local topological order.