New project
Coherent microlaser networks as computational tool

Despite large advances in both algorithms and computer technology, even typical instances of certain computationally hard problems (NP-hard) may be too difficult to be solved on today’s computers. In certain areas of application unconventional computational devices could help to overcome these limitations. In this project, a complex network of microlasers with tuneable tunnel couplings will be tested for its suitability as computational tool in optimisation tasks.


Thermodynamics at the nanoscale

Advances in micro- and nano-technology allow for testing concepts derived from classical thermodynamics in regimes where the underlying assumptions, such as the thermodynamic limit and thermal equilibrium, no longer hold. Single-particle heat machines provide an excellent platform to test theoretical advances in and our understanding of thermodynamics at the micro- and nano-scale. In this project, a minimalist heat engine has been realized that takes advantage of squeezed heat to outperform conventional heat engines. The non-equilibrium nature of these reservoirs permit work extraction from a single reservoir and engine efficiencies unbounded by the standard Carnot limit. A major open question remains whether highly miniaturized heat engines will be able to use the extracted work to accomplish mesoscopic tasks as transporting particles or manipulating biological matter.

Key publications

  • J. Klaers, S. Faelt, A. Imamoglu, and E. Togan, “Squeezed thermal reservoirs as a resource for a nano-mechanical heat engine beyond the Carnot limit”, Physical Review X 7, 031044 (2017). link


Bose-Einstein condensation of photons


Its bosonic and ideal (interaction-free) nature should make a photon gas an obvious candidate for a Bose-Einstein condensation. However, the thermodynamic behavior of photon gases usually does not include a condensation process. For blackbody radiation, the most omnipresent Bose gas, the number of photons follows the available thermal energy. At low temperatures, the photon number simply decreases and no macroscopic occupation of the cavity ground state occurs. In contrast to a three-dimensional thermal photon gas as Planck’s blackbody radiation, photons can exhibit Bose-Einstein condensation, if the thermalization process is restricted to two motional degrees of freedom. Experimentally, this situation has been realized in a microcavity enclosing a dye medium, designated as a room temperature heat bath for the photon gas. Detailed experimental studies of the thermalization and condensation process, as well as the quantum statistics of the photon condensate, have revealed the signatures of this unusual ‘superfluid’.

Key publications

  • D. Dung, C. Kurtscheid, T. Damm, J. Schmitt, F. Vewinger, M. Weitz, and J. Klaers, “Variable potentials for thermalized light and coupled condensates”, Nature Photonics 11, 565 (2017). link
  • J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, ”Bose-Einstein condensation of photons in an optical microcavity”, Nature 468, 545 (2010). link
  •  J. Klaers, F. Vewinger, and M. Weitz, “Thermalization of a two-dimensional photonic gas in a ‘white wall’ photon box”, Nature Physics 6, 512 (2010). link