5th Institute of Physics

Former Projects

Past activities in our laboratories.

Novel sources of ultra cold matter

Continuous Loading Scheme (c)
Scheme of the continuous loading scheme. For incoming atoms in a low-field seeking state the trap potential is repulsive. Once this barrier has stopped the atoms, they are transferred to the absolute ground state, where the hybrid potential is attractive.

We studied a new approach to reach quantum degeneracy for situations when standard laser cooling mechanisms are not applicable, e.g. due to the lack of a closed cycling transition. An optical dipole trap (ODT) is continously loaded from a guided atomic beam with a mechanism that can be compared to a diode for atoms. An ODT is therefore placed within an atomic beam. A state dependent potential barrier superimposed to the trap removes the directed kinetic energy from the atoms, while they are traveling through the ODT's focus. This dissipative mechanism is in principle a single photon process, and not depending on a closed cycling transition. Loading the trap until it reaches the collisionally dense regime then allows further cooling by evaporation.

With this method, we managed to produce a BEC with chromium atoms within less than 5s. While we did not use laser cooling to generate our beam of chromium atoms, there are methods to generate intense beams with molecules that have recently been established and which are not based on cycling transitions.

[1] A. Griesmaier, J. Werner, S. Hensler, J. Stuhler, and T. Pfau
"Bose-Einstein condensation of chromium"
Phys. Rev. Lett. 94, 160401 (2005)
[2] A. Greiner, J. Sebastian, P. Rehme, A. Aghajani-Talesh, A. Griesmaier, and T. Pfau
"Loading chromium atoms in a magnetic guide"
J. Phys. B, 40 F77 (2007)
[3] A. Griesmaier, A. Aghajani-Talesh, M. Falkenau, J. Sebastian, A. Greiner, and T. Pfau
"A high flux of ultra-cold chromium atoms in a magnetic guide"
J. Phys. B: At. Mol. Opt. Phys. 42 145306 (2009)
[4] A. Aghajani-Talesh, M. Falkenau, A. Griesmaier and T. Pfau
"A proposal for continuous loading of an optical dipole trap with magnetically guided ultra cold atoms"
J. Phys. B: At. Mol. Opt. Phys. 42 245302 (2009)
[5] A. Aghajani-Talesh, M. Falkenau, V.V. Volchkov, L.E. Trafford, T. Pfau, and A. Griesmaier
"Laser cooling of a magnetically guided ultra cold atom beam"
New J. Phys. 12 065018 (2010)
[6] M. Falkenau, V. V. Volchkov, J. Rührig, A. Griesmaier, and T. Pfau
"Continuous Loading of a Conservative Trap from an Atomic Beam"
Phys. Rev. Lett. 106, 163002 (2011)
[7] M. Falkenau, V. V. Volchkov, J. Rührig, H. Gorniaczyk, and A. Griesmaier
"Evaporation-limited loading of an atomic trap"
Phys. Rev. A 85, 023412 (2012)
[8] V. V. Volchkov, J. Rührig, T. Pfau, and A. Griesmaier
"Sisyphus cooling in a continuously loaded trap"
New J. Phys. 15 093012 (2013)
[9] V. V. Volchkov, J. Rührig, T. Pfau, and A. Griesmaier
"Efficient demagnetization cooling of atoms and its limits"
Phys. Rev. A 89, 043417 (2014)
[10] J. Rührig, T. Bäuerle, A. Griesmaier, and T. Pfau
"High efficiency demagnetization cooling by suppression of light-assisted collisions"
Opt. Express 23, 5596-5606 (2015) [Focus Issue: Optical Cooling and Trapping]
[11] J. Rührig, T. Bäuerle, P. S. Julienne, E. Tiesinga, and T. Pfau
"Photoassociation of spin polarized Chromium"
Phys. Rev. A 93, 021406 (2016)

Strongly interacting Rydberg gases

Setup of the first generation Rydberg experiment (c)
Experimental setup: (a) schematical view (b) picture of the BEC chamber from inside. Eight electric field plates inside the BEC-vacuum chamber allow us to control the electric field at the position of the atoms and to field ionize Rydberg atoms.

In our first generation Rubidium Rydberg experiment, we have started our long-standing endeavor to probe and control giant Rydberg atoms in an ultracold atomic gas. The apparatus used a single chamber approach, where MOT and magnetic trap are located at the same spot. The MOT was loaded from a Zeeman slower, followed by a magnetic cloverleaf trap, in which BECs containing ~105 atoms have been produced. The magnetic trap is located at the center of 8 electric field plates (see figure) which can produce strong electric fields for tuning and ionization of the Rydberg atoms.

Our experiments started with detailed studies of interactions between Rydberg atoms (dipole-dipole and van der Waals interaction), tuning of interactions via Förster resonances, and the demonstration of the first excitation of Rydberg atoms in a Bose-Einstein condensate. The excitation of Rydberg atoms in a dense an ultracold atomic ensemble lead to the experimental discovery of a new type of molecular bond between Rydberg and ground state atoms, forming an ultralong-range Rydberg molecule. We have investigated the nature of this binding mechanism in detail, demonstrated coherent control of the long-range dimers, and studied the transition from few-body bound states to many-body density shifts.

[1] A. Grabowski, R. Heidemann, R. Löw, J. Stuhler, and T. Pfau
"High Resolution Rydberg Spectroscopy of ultracold Rubidium Atoms"
Fortschr. Phys. 54, 765 (2006)
[2] R. Heidemann, U. Raitzsch, V. Bendkowsky, B. Butscher, R. Löw, L. Santos, and T. Pfau
"Evidence for coherent collective Rydberg excitation in the strong blockade regime"
Phys. Rev. Lett. 99, 163601 (2007)
[3] U. Raitzsch, V. Bendkowsky, R. Heidemann, B. Butscher, R. Löw, and T. Pfau
"An echo experiment in a strongly interacting Rydberg gas"
Phys. Rev. Lett. 100 , 013002 (2008)
[4] R. Heidemann, U. Raitzsch, V. Bendkowsky, B. Butscher, R. Löw, and T. Pfau
"Rydberg excitation of Bose-Einstein condensates"
Phys. Rev. Lett. 100, 033601 (2008)
[5] H. Weimer, R. Löw, T. Pfau, H. P. Büchler
"Quantum critical behavior in strongly interacting Rydberg gases"
Phys. Rev. Lett. 101, 250601 (2008)
[6] V. Bendkowsky, B. Butscher, J. Nipper, J. P. Shaffer, R. Löw, and T. Pfau
"Observation of ultralong-range Rydberg molecules"
Nature 458, 1005-1008 (2009)
[7] V. Bendkowsky, B. Butscher, J. Nipper, J. Balewski, J. P. Shaffer, R. Löw, T. Pfau, W. Li, J. Stanojevic, T. Pohl, and J. M. Rost
"Rydberg trimers and excited dimers bound by internal quantum reflection"
Phys. Rev. Lett. 105, 163201 (2010)
[8] B. Butscher, J. Nipper, J. B. Balewski, L. Kukota, V. Bendkowsky, R. Löw, and T. Pfau
"Atom-molecule coherence for ultralong range Rydberg dimers"
Nature Physics 6, 970–974 (2010)
[9] B. Butscher, V. Bendkowsky, J. Nipper, J. B. Balewski, L. Kukota, R. Löw, T. Pfau W. Li, T. Pohl, and J. M. Rost
"Lifetimes of ultralong-range Rydberg molecules in vibrational ground and excited states"
J. Phys. B: At. Mol. Opt. Phys. 44, 184004 (2011)
[10] W. Li, T. Pohl, J. M. Rost, Seth T. Rittenhouse, H. R. Sadeghpour, J. Nipper, B. Butscher, J. B. Balewski, V. Bendkowsky, R. Löw, and T. Pfau
"A Homonuclear Molecule with a Permanent Electric Dipole Moment"
Science 334, 1110 (2011)
[11] J. Nipper, J. B. Balewski, A. T. Krupp, B. Butscher, R. Löw, and T. Pfau
"Highly Resolved Measurements of Stark-Tuned Förster Resonances between Rydberg Atoms"
Phys. Rev. Lett. 108, 113001 (2012)
[12] R. Löw, H. Weimer, J. Nipper, J. B. Balewski, B. Butscher, H. P. Büchler, and T. Pfau
"An experimental and theoretical guide to strongly interacting Rydberg gases"
J. Phys. B: At. Mol. Opt. Phys. 45, 113001 (2012)
[13] J. Nipper, J. B. Balewski, A. T. Krupp, S. Hofferberth, R. Löw, and T. Pfau
"Atomic Pair-State Interferometer: Controlling and Measuring an Interaction-Induced Phase Shift in Rydberg-Atom Pairs"
Phys. Rev. X 2, 031011 (2012)
[14] J. B. Balewski, A. T. Krupp, A. Gaj, D. Peter, H. P. Büchler, R. Löw, S. Hofferberth, and T. Pfau
"Coupling a single electron to a Bose-Einstein condensate"
Nature 502, 664 (2013)
[15] J.B. Balewski, A.T. Krupp, A. Gaj, S. Hofferberth, R. Löw, and T. Pfau
"Rydberg dressing: Understanding of collective many-body effects and implications for experiments"
New J. Phys. 16 063012 (2014)
[16] A.T. Krupp, A. Gaj, J.B. Balewski, P. Ilzhöfer, S. Hofferberth, R. Löw, T. Pfau, M. Kurz, and P. Schmelcher
"Alignment of D-state Rydberg molecules"
Phys. Rev. Lett. 112, 143008 (2014)
[17] T. Karpiuk, M. Brewczyk, K. Rzążewski, A. Gaj, J. B. Balewski, A. T. Krupp, M. Schlagmüller, R. Löw, S. Hofferberth, and T. Pfau
"Detecting and imaging single Rydberg electrons in a Bose-Einstein condensate"
New Journal of Physics, 17, 053046 (2015)
[18] A. Gaj, A. T. Krupp, J. B. Balewski, R. Löw, S. Hofferberth, and T. Pfau
"From molecular spectra to a density shift in dense Rydberg gases"
Nature Comm. 5, 4546 (2014)
[19] K. R. A. Hazzard, M. van d. Worm, M. Foss-Feig, S. R. Manmana, E. D. Torre, T. Pfau, M. Kastner, A. M. Rey
"Quantum correlations and entanglement in far-from-equilibrium spin systems"
Phys. Rev. A 90, 063622 (2014)
[20] A. Gaj, A. T. Krupp, P. Ilzhöfer, R. Löw, S. Hofferberth, T. Pfau
"Hybridization of Rydberg electron orbitals by molecule formation"
Phys. Rev. Lett., 115 , 023001 (2015)

Rydberg Quantum Optics

The Rydberg Quantum Optics Group led by Sebastian Hofferberth moved to Syddansk University (Odense, Denmark). The website of Sebastian's group can be found here.

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