ELFT HÍRADÓ

[geszti AT complex.elte.hu]

                                 MEGHÍVÓ

           az ELTE Komplex Rendszerek Fizikája Tanszék teájára

                               Fortágh József

CQ Center for Collective Quantum Phenomena and their Applications
 University of Tübingen
 Auf der Morgenstelle 14, D-72076 Tübingen, Germany
 www.pit.physik.uni-tuebingen.de/fortagh


                      Interfacing cold atoms and solids

Trapping and manipulating atoms by means of microscopic traps has seen  
enormous advances within the last decade. Today, ultra-cold atom  
clouds, Bose-Einstein condensates, and Fermi gases are routinely  
trapped in conservative potential at the surface of microchips [1].  
Such experiments have delivered important insights into fundamental  
interactions between atoms and surfaces and pave the way towards the  
coherent coupling between atoms and quantum electronic circuits.

In our experiments, we investigate the quantum interface between  
atomic clouds and superconducting devices. In general, the state of a  
superconducting quantum bit can be manipulated at microelectronic  
rates. However, its decoherence is fast due to the coupling to the  
thermal environment. Transferring the quantum state to cold atoms as  
quantum memory may bridge sort and long time scales. We develop  
experimental techniques towards the realization of such solid  
state-atomic-light quantum interfaces. I report the realization of a  
trapped rubidium atomic clock on a superconducting chip. We use the  
atomic clock to demonstrate the long coherence time of atomic  
superposition states near the superconductor, which is necessary for  
constructing a long living quantum memory [2].

Another subject of our research is the development of integrated  
quantum sensors based on ultra-cold atoms. I describe the application  
of ultra-cold atom clouds as the “tip” of a scanning probe microscope  
[3]. This tip (typically 103–105 atoms, density 1012–1014 cm-3,  
temperature 10nK–1ľK) is scanned in a three-dimensional volume above  
the surface of interest by means of a magnetic “conveyor belt”. Analog  
to AFMs, the cold-atom scanning probe microscope (CA-SPM) can be  
operated in contact and dynamical modes for imaging surface  
topographies and for ultrasensitive force measurements [4].


References
 1. J. Fortágh, C. Zimmermann, “Magnetic microtraps for ultracold atoms”,
 Reviews of Modern Physics 79, 235 (2007).
 2. S. Bernon et al., arXiv:1302.6610 (2013).
 3. M. Gierling et al., “Cold-atom scanning probe microscopy”,
 Nature Nanotechnology 6, 446-451 (2011).
 4. P. Schneeweiß et al., “Dispersion forces between ultracold atoms  
and a carbon nanotube”,
 Nature Nanotechnology 7, 515-519 (2012)

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