It has been a longstanding goal to realize a hybrid system that interfaces single or ensembles of atoms in Rydberg states to chip-based microwave photons in a circuit quantum electrodynamics system operating at cryogenic temperatures. However, a working system could not be achieved so far because of fundamental and technical challenges that are linked to the sensitivity of Rydberg atoms to surface imperfections such as patches of adsorbates, local charges or potential differences. Static and time-dependent inhomogeneous stray electric fields emanating from these imperfections result in strong decoherence of the atom cloud and tools to avoid or characterize and compensate these fields need to be developed.
In this talk we present a new setup in which decoherence due to stray electric fields that emanate from surfaces at cryogenic temperatures can be measured and reduced.
Specifically, we show how helium atoms in Rydberg states with principal quantum number n between 30 and 40 were manipulated coherently with microwave radiation pulses near planar gold surfaces, and near transmission lines patterned onto either a printed-circuit board or onto a superconducting NbTiN surface. All surfaces were cooled to cryogenic temperatures.
The coherent manipulation of the ns Rydberg states with pulsed microwave radiation above the surfaces enabled precise measurements of static and microwave electric fields and allowed studying the decoherence of the atomic ensemble.
The results of this work represent important milestones toward a working hybrid system with Rydberg atoms and coplanar microwave resonators. The techniques to avoid and compensate stray electric fields allowed to preserve coherence of the atomic sample for several microseconds above cold, patterned surfaces for the first time without specific modifications to the design of the surface properties. This opens a clear path toward a non-destructive detection of Rydberg atoms using a small number of microwave photons in a planar waveguide resonator.