Research Projects

Our understanding of open quantum systems is becoming ever more central for progress in quantum science and engineering. In open systems, a small quantum system is in contact with a huge environment and thus experiences de-coherence. Theory is in demand for creating more complex and smaller nano-technological devices and turning de-coherence from an obstacle into an asset. This project addresses both challenges through theory of highly excited Rydberg atoms, interacting with a thermal gas or Bose-Einstein condensate (BEC) environment. These hybrid systems are at the forefront of cold atom experiments. With the Rydberg atoms as quantum system and the BEC as environment, this setup provides a controllable platform for quantum simulations and studies of de-coherence. While our theory will benefit all scientific disciplines with open-quantum systems, our main push will be towards ultracold quantum chemistry (the smallest possible nano-device: a molecule) and spin-systems within functionalised or suppressed decoherence. We shall explore the ultracold chemistry of ultra-long-range molecules, in which ground-state atoms are bound to a Rydberg ionic core through elastic scattering off the Rydberg electron from the ground-state atoms, featuring bond-lengths near micrometers. Then, molecular dynamics and reactions can be affected by thousands of ambient medium atoms, which should make reactions depend on the degree of spatial quantum coherence of the ambient medium, which can range from none, in a thermal gas, over a finite coherence length near condensation or in quasi-condensate down to coherence extending over the entire medium in a BEC. Unravelling molecular mechanism driven by the quantum coherent dynamics of the medium itself has the potential to truly open up an “ultracold” sub-discipline of quantum chemistry. Mapping two different internal Rydberg states such as l=0 and l=1 angular momentum onto a pseudospin, we can form complex spin arrays, which are embedded in the host cold gas or BEC in which the Rydberg atoms were excited. We have earlier shown, how either a Bose-Einstein condensate decoheres and relaxes such spin systems, with the environmental correlation times under some degree of control. Here we propose to leverage this to investigate quantum defect formation during quenches, within systems in contact with this tunable BEC environment. For this we will combine key strengths of the group of the PI and the co-PI and are thus in a unique position to execute this research. Due to the very long memory times of a BEC environment, we will venture into new territory regarding open quantum phase transitions, with insight impacting devices such as smart materials, adiabatic quantum computers or defect based computing. Both avenues will yield interdisciplinary long term benefits, where we envisage quantum coherent molecular machines, or fast switching quantum materials reliant on taylored environmental correlations.