5th Institute of Physics

Giant Rydberg Atoms in ultracold quantum gases

Rydberg Impurities in a Bose-Einstein Condensate

Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics


Rydberg atoms, excited atoms with the outermost electron residing in orbitals of high principal quantum number, are fascinating objects with extreme properties. For instance, their electron orbits can reach the micrometer scale, they feature giant mutual interactions, and have extremely long lifetimes compared to electronic excitations in low-n orbitals. We study Rydberg atoms when immersed in an ultracold quantum gas, with specific focus their role as single or few mesoscopic impurities that interact collectively with the atomic ensemble.

Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics


Figure 1: Illustration of a Rydberg atom excited from a Bose-Einstein condensate. Recently, we have observed evidence for the interaction of the ionic core (yellow) with the condensate atoms (green), while the electron (blue) is brought to giant Rydberg orbits.

Our experiments focus on the study of single Rydberg atoms embedded in an ultracold quantum gas at temperatures in the nanokelvin regime. Our ability to control such Rydberg impurities with principal quantum numbers up to n~200 allows us to investigate situations where the size of the Rydberg atom by far extends the typical distance between the trapped atoms. This provides ways to investigate the interaction of the Rydberg electron with single, few, or many neutral perturbers residing within the electronic orbital. The quantum mechanical scattering process describing this interaction leads to a new molecular bond and the formation of giant so-called ultralong-range Rydberg molecules. For many perturbers within the Rydberg orbit, which is realized when exciting the Rydberg state in a Bose-Einstein condensate, the contribution of higher-order partial waves in the electron-neutral scattering process can be studied. Specifically, a detailed modelling of the excitation lineshape, which is strongly shifted and broadened by the interaction with the condensate, reveals signatures of an electron-atom p-wave scattering resonance. Moreover, the lifetime of the Rydberg electron in the dense medium is determined by chemical reactions on micrometer length scales and microsecond time scales, leading to molecular ion formation and collision-induced changes of the electron’s orbital angular momentum. In this regime, we are currently pursuing to observe the backaction of the Rydberg electron on the condensate density distribution, a mechanism that may lead to a microscopy tool for electronic orbitals.

Very recently, we have focused on the interaction of the positively charged ionic Rydberg core with the Bose-Einstein condensate. This ion-atom interaction is much weaker than the electron-atom interaction and typically fully disguised by the latter. However, the contribution of the electron can be largely reduced once its orbit exceeds the typical size of the atomic sample. At the same time, the presence of the electron serves as a protective Faraday shield for the ion from detrimental electric stray fields. We demonstrate this regime using a micron-sized optical tweezer trap and observe evidence for ion-atom interaction. These experiments may lead to a new way for studying ionic impurities in a BEC at temperatures where quantum effects in the scattering process start to play a role, with prospects for the exploration of associated polaron physics.

Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics

Our setups

Figure 2: In-vacuum electric field control for exciting high-n Rydberg states. Electric field plates are combined with ports for optical access, one of which holds a high-NA lens for local addressing and readout.

In our apparatus, we employ combinations of magnetic and optical trapping and cooling techniques to achieve Bose-Einstein condensation of 87Rb inside an in-chamber electric field control cage, which allows us to create single Rydberg atoms with principal quantum number up to n~200. Rydberg states are conveniently accessed via a two-photon transition with lasers at 420nm and 1020nm, both stabilized to a high-finesse optical cavity for high-resolution Rydberg spectroscopy. Efficient detection of single Rydberg atoms is achieved by means of electric field ionization and ion detection using either a microchannel plate (MCP) or a channeltron.

Additionally, our apparatus hosts an in-vacuum aspheric lens for high-resolution in-situ imaging and addressing of our condensate. This provides means to create localized Rydberg impurities at well defined positions. Apart from spectroscopic studies of the impurity, the apparatus is specifically designed to investigate the effect of the impurity on the condensate density distribution with sub-micrometer optical resolution.

Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics


10.05.2018An ionic impurity in a Bose-Einstein condensate at sub-microkelvin temperatures more...
04.05.2017Spin-orbit coupling provides access to trilobite Rydberg molecules more...
10.08.2016Ultracold Chemical Reactions of a Single Rydberg Atom in a Dense Gas more...
21.04.2016Observation of mixed singlet-triplet Rb2 Rydberg molecules more...
18.06.2015Probing a scattering resonance in Rydberg molecules with a Bose-Einstein condensate more...

Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics

The Crew

Thomas Dieterle(Doktorand)
Carolin Dietrich(Master Student)
Felix Engel(Doktorand)
Kathrin Kleinbach(Doktorandin)
Robert Löw(Group leader)
Florian Meinert(Post Doc)
Tilman Pfau(Institutsleiter)

Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics

Open Positions

quantum mechanical wave function of a giant Rydberg moleculeWe are always looking for motivated people to join our Rydberg team.

We are currently trying to spatially image an electron wave function directly by its interaction with a Rb Bose-Einstein Condensate. For this we are looking for

  • a Master student
  • a PhD student

If you are interested in our effort to understand the physics of Rydberg atoms in quantum gases , contactmailto icon F. Meinert, mailto icon R. Löw, or mailto icon T. Pfau via email/phone or just come by and visit our labs (5.125).


Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics

Refs & Publications

[1]M. Schlagmüller, T. C. Liebisch, H. Nguyen, G. Lochead, F. Engel, F. Böttcher, K. M. Westphal, K. S. Kleinbach, R. Löw, S. Hofferberth, T. Pfau, J. Pérez-Ríos, C. H. Greene
"Probing an Electron Scattering Resonance using Rydberg Molecules within a Dense and Ultracold Gas"
Phys. Rev. Lett. 116, 053001 (2016) , arXiv:1510.07003; doi: 10.1103/PhysRevLett.116.053001
[2]F. Böttcher, A. Gaj, K. M. Westphal, M. Schlagmüller, K. S. Kleinbach, R. Löw, T. Cubel Liebisch, T. Pfau, and S. Hofferberth
"Observation of mixed singlet-triplet Rb2 Rydberg molecules"
Phys. Rev. A 93, 032512 (2016) , arXiv:1510.01097; doi: 10.1103/PhysRevA.93.032512
[3]M. Schlagmüller, T. C. Liebisch, F. Engel, K. S. Kleinbach, F. Böttcher, U. Hermann, K. M. Westphal, A. Gaj, R. Löw, S. Hofferberth, T. Pfau, J. Pérez-Ríos, and C. H. Greene
"Ultracold Chemical Reactions of a Single Rydberg Atom in a Dense Gas"
Phys. Rev. X 6, 031020 (2016) , arXiv:1605.04883; doi: 10.1103/PhysRevX.6.031020
[4]T. C. Liebisch, M. Schlagmüller, F. Engel, H. Nguyen, J. Balewski, G. Lochead, F. Böttcher, K. M. Westphal, K. S. Kleinbach, T. Schmid, A. Gaj, R. Löw, S. Hofferberth, T. Pfau, J. Pérez-Ríos and C. H. Greene
"Controlling Rydberg atom excitations in dense background gases"
J. Phys. B: At. Mol. Opt. Phys. 49, (2016) 182001 , arXiv:1607.01325; doi: 10.1088/0953-4075/49/18/182001
[5]Krzysztof Jachymski, Florian Meinert, Hagar Veksler, Paul S. Julienne, and Shmuel Fishman
"Ultracold atoms in quasi-1D traps: a step beyond the Lieb-Liniger model"
Phys. Rev. A 95, 052703 (2017) ; arXiv:1703.08364; doi: 10.1103/PhysRevA.95.052703
[6]K. Kleinbach, F. Meinert, F. Engel, W. Kwon, R. Löw, T. Pfau, G. Raithel
"Photoassociation of Trilobite Rydberg Molecules via Resonant Spin-Orbit Coupling"
Phys. Rev. Lett. 118, 223001 (2017); arXiv:1703.01096; doi: 10.1103/PhysRevLett.118.223001
[7]Florian Meinert
"Riesenmoleküle am absoluten Nullpunkt"
Phys. Unserer Zeit 48, 236–242 (2017) ; doi: 10.1002/piuz.201701478
[8]K. S. Kleinbach, F. Engel, T. Dieterle, R. Löw, T. Pfau, F. Meinert
"Ionic Impurity in a Bose-Einstein Condensate at Submicrokelvin Temperatures"
Phys. Rev. Lett. 120, 193401; arXiv:1802.08587 (2018); doi: 10.1103/PhysRevLett.120.193401

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Bachelor- and Master-Topics

Characterization of an optical tweezer for far-detuned trapping of ions  (Bachelor Thesis)

In our experiment, we plan to implement optical trapping of single ionic impurities that we create by photo-ionization of parent Rydberg impurities. For this to realize it is of importance to characterize the beam profile of a micro-meter sized optical tweezer. You will develop a fully automized Piezo-based scanning system to measure the point-spread-function of a micro-tweezer generated from a high-NA aspheric lens. The goal is to identify optimal laser beam parameters to balance diffraction limited performance and undesired geometric aberrations in view of realizing minimal spot sizes.


  F.Meinert, K.Kleinbach, F. Engel, T. Pfau


High resolution Rydberg spectroscopy in a Bose-Einstein Condensate (Master Thesis) 

A  Rydberg atom provide a single electron in a well defined quantum state that can cover thousands of atoms in a Bose-Einstein Condensate. We are interested to watch this single quantum imersed in a sea of atoms. On the one hand it can bind atoms into molecular states on the other habe it can backact on the collective excitations of a quantum gas. The interaction between the electron and the quantum gas is mediated by low energy scattering. The interaction depends on the electron spin and we have recently studies how this spin dependence can be used to excite very exotic "trilobite" molecules (see figure above) [2]. In this thesis we want to understand the transition from molecular physics to many-body physics [3] including the spin degree of freedom. In addition we want to study the depencence on the orbital angular momentum [4]. The experimenatl tool is high resolution spectroscopy on a BEC sample including single ion detection.


[1] Kathrin S. Kleinbach, Florian Meinert, Felix Engel, Woo Jin Kwon, Robert Löw, Tilman Pfau, Georg Raithel
"Photo-association of trilobite Rydberg molecules via resonant spin-orbit coupling"
Phys. Rev. Lett. 118, 223001 (2017)

[2] 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)

[3] 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)


  F.Meinert, K.Kleinbach, F. Engel, T. Pfau


Abstract | Research | Our setups | Highlights | The Crew | Open Positions | Refs & Publications | Bachelor- and Master-Topics