5th Institute of Physics

Dipolar Quantum Gases

Dipolar quantum gases featuring long range and anisotropic interactions and the search for novel states of matter and collective phenomena

The Project

In 2005 we produced the first Chromium-BEC and we showed that it exhibits non-negligible dipolar effects. Nevertheless, the dipole-dipole interactions were only a small perturbation compared to the usual contact interactions. After exploring a lossless cooling method for a thermal cloud, which exploits the fast dipolar relaxation, we focused on the strong-dipolar effects in the quantum degenerate regime. In 2007 we achieved the first quantum ferrofluid, i.e. a BEC with comparable contact and dipole-dipole interactions, and shortly afterwards a purely dipolar BEC. Due to the anisotropic character of the dipole-dipole interactions the stability the BEC depends on the trap geometry and shows an universal behavior in the large N regime. We have observed instabilities - the so-called  dipolar collapse involving an anisotropic d-wave symmetry. We have then investigated the phase coherence of collapsed condensates. We induced the collapse in several condensates simultaneously and let them interfere. By observing high fringe contrast, we proved that the collapsed cloud contains a remnant condensate. Also dipolar interaction in optical lattices was observed.

Since 2014 we have replaced the Chromium quantum gas by a Dysprosium BEC. Dysprosium has the highest magnetic moment of all atoms in the periodic table and due to its larger mass a reduced contact interaction. It is therefore best suited to study the dipolar phenomena. With this new system we have observed the equivalent of the Rosensweig instability which happens for classical ferrofluids, with our dipolar BEC, a quantum ferrofluid. This instability is characterized by the formation of regular patterns of peaks and valleys in the denity of the BEC.

 (c) Universität Stuttgart
Illustration of the behaviour of a quantum ferrofluid: When the quantum ferrofluid is placed in a flat "pancake" trap (left), decreasing the contact interaction such that the gas becomes dominated by the dipolar interaction results in the formation of stable density waves and eventually of droplets (right). This is the equivalent of the rosensweig instability of classical ferrofluid. Photo: Universität Stuttgart

As opposed to what was previously thought, the resulting state is actually stable, characterized by the formation of droplets. These droplets are actually made of a novel quantum liquid, where the attraction due to the dipolar interaction, which tends to drive a collapse, is balanced by quantum fluctuations of the BEC field as dictated by Heisenberg uncertainty principle. 

Universität Stuttgart (c)
Formation of droplets as observed in our Dysprosium dipolar quantum gas

Based on this,we succeeded in proving experimentally that the long-sought supersolid state of matter exists in 2019. Such a supersolid is a counterintuitive state of matter that is both solid and fluid at the same time. The definitive proof that the regular patterns observed in the experiment form indeed a supersolid relies on our observation of two kinds of sound waves. Such sound waves propagate differently in different materials – in air, for example, sound waves travel much slower than in water. This "normal" sound wave is also present in the supersolid. However, because the supersolid is both solid and fluid, a characteristic second form of sound wave can be observed, in which the crystal and the superfluid move against each other. This results in sound waves that travel at very low speeds, which we were able to observe for the first time in our experiment.

 (c) Universität Stuttgart
Figure a) shows a small crystal, c) shows a superfluid prepared from ultracold atoms, and b) shows the superposition of the crystal and the superfluid - the so called supersolid. Within a certain parameter range, the two states of matter "solid" and "fluid", which are mutually exclusive in the classical world, can exist simultaneously in the quantum world.

Project Publications

  1. 2019

    1. Mennemann, J.-F., Langen, T., Exl, L., Mauser, N.J.: Optimal control of the self-bound dipolar droplet formation process. Computer Physics Communications. 244, 205--216 (2019). https://doi.org/10.1016/j.cpc.2019.06.002.
    2. Hertkorn, J., Böttcher, F., Guo, M., Schmidt, J.N., Langen, T., Büchler, H.P., Pfau, T.: Fate of the Amplitude Mode in a Trapped Dipolar Supersolid. Phys. Rev. Lett. 123, 193002 (2019). https://doi.org/10.1103/PhysRevLett.123.193002.
    3. Guo, M., Böttcher, F., Hertkorn, J., Schmidt, J.-N., Wenzel, M., Büchler, H.P., Langen, T., Pfau, T.: The low-energy Goldstone mode in a trapped dipolar supersolid. Nature. 574, 386--389 (2019). https://doi.org/10.1038/s41586-019-1569-5.
    4. Böttcher, F., Wenzel, M., Schmidt, J.-N., Guo, M., Langen, T., Ferrier-Barbut, I., Pfau, T., Bomb\’ın, R., Sánchez-Baena, J., Boronat, J., Mazzanti, F.: Dilute dipolar quantum droplets beyond the extended Gross-Pitaevskii equation. Phys. Rev. Research. 1, 033088 (2019). https://doi.org/10.1103/PhysRevResearch.1.033088.
    5. Böttcher, F., Schmidt, J.-N., Wenzel, M., Hertkorn, J., Guo, M., Langen, T., Pfau, T.: Transient Supersolid Properties in an Array of Dipolar Quantum Droplets. Phys. Rev. X. 9, 011051 (2019). https://doi.org/10.1103/PhysRevX.9.011051.
  2. 2018

    1. Langen, T., Mark, M.J.: Ultrakalt magnetisiert. Physik Journal. 17, 35 (2018).
    2. Ferrier-Barbut, I., Wenzel, M., Böttcher, F., Langen, T., Pfau, T.: Onset of a modulational instability in trapped dipolar Bose-Einstein condensates. Phys. Rev. A. 97, 011604 (2018). https://doi.org/10.1103/PhysRevA.97.011604.
    3. Ferrier-Barbut, I., Pfau, T.: Quantum liquids get thin. Science. 359, 274 (2018). https://doi.org/10.1126/science.aar3785.
    4. Wenzel, M., Böttcher, F., Schmidt, J.-N., Eisenmann, M., Langen, T., Pfau, T., Ferrier-Barbut, I.: Anisotropic Superfluid Behavior of a Dipolar Bose-Einstein Condensate. Phys. Rev. Lett. 121, 030401 (2018).
    5. Ferrier-Barbut, I., Wenzel, M., Böttcher, F., Langen, T., Isoard, M., Stringari, S., Pfau, T.: Scissors Mode of Dipolar Quantum Droplets of Dysprosium Atoms. Phys. Rev. Lett. 120, 160402 (2018). https://doi.org/10.1103/PhysRevLett.120.160402.
  3. 2017

    1. Wenzel, M., Böttcher, F., Langen, T., Ferrier-Barbut, I., Pfau, T.: Striped states in a many-body system of tilted dipoles. Phys. Rev. A. 96, 053630 (2017). https://doi.org/10.1103/PhysRevA.96.053630.
  4. 2016

    1. Schmitt, M., Wenzel, M., Böttcher, B., Ferrier-Barbut, I., Pfau, T.: Self-bound droplets of a dilute magnetic quantum liquid. Nature. 539, 259 (2016). https://doi.org/10.1038/nature20126.
    2. Kadau, H., Schmitt, M., Wenzel, M., Wink, C., Maier, T., Ferrier-Barbut, I., Pfau, T.: Observing the Rosensweig instability of a quantum ferrofluid. Nature. 530, 194 (2016). https://doi.org/10.1038/nature16485.
    3. Ferrier-Barbut, I.: Smashing magnets. New Journal of Physics. 18, 111004 (2016). https://doi.org/10.1088/1367-2630/18/11/111004.
    4. Ferrier-Barbut, I., Schmitt, M., Wenzel, M., Kadau, H., Pfau, T.: Liquid quantum droplets of ultracold magnetic atoms. J. Phys. B: At. Mol. Opt. Phys. 49, 214004 (2016). https://doi.org/10.1088/0953-4075/49/21/214004.
    5. Ferrier-Barbut, I., Kadau, H., Schmitt, M., Wenzel, M., Pfau, T.: Observation of quantum droplets in a strongly dipolar Bose gas. Phys. Rev. Lett. 116, 215301 (2016). https://doi.org/10.1103/PhysRevLett.116.215301.
  5. 2015

    1. Karpiuk, T., Brewczyk, M., Rzążewski, K., Gaj, A., Balewski, J.B., Krupp, A.T., Schlagmüller, M., Löw, R., Hofferberth, S., Pfau, T.: Imaging single Rydberg electrons in a Bose–Einstein condensate. New Journal of Physics. 17, 053046 (2015). https://doi.org/10.1088/1367-2630/17/5/053046.
    2. Maier, T., Kadau, H., Schmitt, M., Wenzel, M., Ferrier-Barbut, I., Pfau, T., Frisch, A., Baier, S., Aikawa, K., Chomaz, L., Mark, M.J., Ferlaino, F., Makrides, C., Tiesinga, E., Petrov, A., Kotochigova, S.: Emergence of chaotic scattering in ultracold Er and Dy. Phys. Rev. X. 5, 041029 (2015).
    3. Maier, T., Ferrier-Barbut, I., Kadau, H., Schmitt, M., Wenzel, M., Wink, C., Pfau, T., Jachymski, K., Julienne, P.S.: Broad Feshbach resonances in collisions of ultracold Dysprosium atoms. Phys. Rev. A. 92, 060702(R) (2015).
  6. 2014

    1. Maier, T., Kadau, H., Schmitt, M., Griesmaier, A., Pfau, T.: Narrow-line magneto-optical trap for dysprosium atoms. Optics Letters. 39, 3138 (2014).
  7. 2013

    1. Bienias, P., Pawlowski, K., Pfau, T., Rzazewski, K.: Ground state of a two component dipolar Fermi gas in a harmonic potential. Phys. Rev. A. 88, 043604 (2013). https://doi.org/10.1103/PhysRevA.88.043604.
    2. Maluckov, A., Gligoric, G., Hadzievski, L., Malomed, B.A., Pfau, T.: High- and low-frequency phonon modes in dipolar quantum gases trapped in deep lattices. Phys. Rev. A. 87, 023623 (2013).
    3. Peter, D., Griesmaier, A., Pfau, T., Büchler, H.P.: Driving dipolar fermions into the quantum Hall regime by spin-flip induced insertion of angular momentum. Phys. Rev. Lett. 110, 145303 (2013).
    4. Schmitt, M., Henn, E.A.L., Billy, J., Kadau, H., Maier, T., Griesmaier, A., Pfau, T.: Spectroscopy of a narrow-line optical pumping transition in dysprosium. Opt. Lett. 38, 637 (2013). https://doi.org/10.1364/OL.38.000637.
    5. Pawlowski, K., Bienias, P., Pfau, T., Rzazewski, K.: Correlations of a quasi-two-dimensional dipolar ultracold gas at finite temperatures. Phys. Rev. A. 87, 043620 (2013). https://doi.org/10.1103/PhysRevA.87.043620.
  8. 2012

    1. Maluckov, A., Gligoric, G., Hadzievski, L., Malomed, B.A., Pfau, T.: Stable periodic density waves in dipolar Bose-Einstein condensates trapped in optical lattices. Phys. Rev. Lett. 108, 140402 (2012).
    2. Billy, J., Henn, E.A.L., Müller, S., Maier, T., Kadau, H., Griesmaier, A., Jona-Lasinio, M., Santos, L., Pfau, T.: Deconfinement-induced collapse of a coherent array of dipolar Bose-Einstein condensates. Phys. Rev. A. 86, 051603(R) (2012). https://doi.org/10.1103/PhysRevA.86.051603.
    3. Peter, D., Pawłowski, K., Pfau, T., Rzążewski, K.: Mean-field description of dipolar bosons in triple-well potentials. J. Phys. B: At. Mol. Opt. Phys. 45, 225302 (2012). https://doi.org/10.1088/0953-4075/45/22/225302.
  9. 2011

    1. Müller, S., Billy, J., Henn, E.A.L., Kadau, H., Griesmaier, A., Jona-Lasinio, M., Santos, L.: Stability of a dipolar Bose-Einstein condensate in a one-dimensional lattice. Phys. Rev. A. 84, 053601 (2011). https://doi.org/10.1103/PhysRevA.84.053601.
  10. 2009

    1. Metz, J., Lahaye, T., Fröhlich, B., Griesmaier, A., Pfau, T., Saito, H., Kawaguchi, Y., Ueda, M.: Coherent collapse of a dipolar Bose-Einstein condensate for different trap geometries. New J. Phys. 11, 055032 (2009).
  11. 2008

    1. Muramatsu, A., (eds.), T.P.: Focus on Quantum Correlations in Tailored Matter. New J. Phys. 10, 045001 (2008).
    2. Lahaye, T., Metz, J., Fröhlich, B., Koch, T., Meister, M., Griesmaier, A., Pfau, T., Saito, H., Kawaguchi, Y., Ueda, M.: d-Wave Collapse and Explosion of a Dipolar Bose-Einstein Condensate. Phys. Rev. Lett. 101, 080401 (2008).
    3. Koch, T., Lahaye, T., Metz, J., Fröhlich, B., Griesmaier, A., Pfau, T.: Stabilizing a purely dipolar quantum gas against collapse. Nature Physics. 4, 218 (2008).
  12. 2007

    1. Fröhlich, B., Lahaye, T., Kaltenhäuser, B., Kübler, H., Müller, S., Koch, T., Fattori, M., Pfau, T.: A two-frequency acousto-optic modulator driver to improve the beam pointing stability during intensity ramps. Rev. Sci. Instrum. 78, 043101 (2007).
    2. Giovanazzi, S., Santos, L., Pfau, T.: Collective oscillations of dipolar Bose-Einstein condensates and accurate comparison between contact and dipolar interaction. Phys. Rev. A. 75, 015604 (2007).
    3. Santos, L., Fattori, M., Stuhler, J., Pfau, T.: Spinor condensates with a laser-induced quadratic Zeeman effect. Phys. Rev. A. 75, 053606 (2007).
    4. Lahaye, Th., Koch, T., Fröhlich, B., Fattori, M., Metz, J., Griesmaier, A., Giovanazzi, S., Pfau, T.: Strong dipolar effects in a quantum ferrofluid. Nature. 448, 672 (2007).
    5. Stuhler, J., Griesmaier, A., Werner, J., Koch, T., Fattori, M., Pfau, T.: Ultracold chromium atoms: From Feshbach resonances to a dipolar Bose-Einstein condensate. J. Mod Opt. 54, 647 (2007).
    6. Glaum, K., Pelster, A., Kleinert, H., Pfau, T.: Critical Temperature of Weakly Interacting Dipolar Condensates. Phys. Rev. Lett. 98, 080407 (2007).
  13. 2006

    1. Fattori, M., Koch, T., Goetz, S., Griesmaier, A., Hensler, S., Stuhler, J., Pfau, T.: Demagnetization cooling of a gas. Nature Physics. 2, 765 (2006).
    2. Griesmaier, A., Stuhler, J., Pfau, T.: Production of a chromium Bose-Einstein condensate. Appl. Phys. B. 82, 211 (2006).
    3. Santos, L., Pfau, T.: Spin-3 Chromium Bose-Einstein Condensates. Phys. Rev. Lett. 96, 190404 (2006).
  14. 2005

    1. Hensler, S., Greiner, A., Stuhler, J., Pfau, T.: Depolarisation cooling of an atomic cloud. Europhys. Lett. 71, 918 (2005).
    2. Stuhler, J., Griesmaier, A., Koch, T., Fattori, M., Giovanazzi, S., Pedri, P., Santos, L., Pfau, T.: Observation of Dipole-Dipole Interaction in a Degenerate Quantum Gas. Phys. Rev. Lett. 95, 150406 (2005).
    3. Griesmaier, A., Werner, J., Hensler, S., Stuhler, J., Pfau, T.: Bose-Einstein condensation of chromium. Phys. Rev. Lett. 94, 160401 (2005).
  15. 2003

    1. Hensler, S., Werner, J., Griesmaier, A., Schmidt, P.O., Görlitz, A., Pfau, T., Giovanazzi, S., Rzazewski, K.: Dipolar Relaxation in an ultra-cold Gas of magnetically trapped chromium atoms. Appl. Phys. B. 77, 765 (2003).

We are looking for motivated new team members!

Magnetic quantum gases and liquids of Dysprosium atoms

We are planning a new setup for a degenerate Dysprosium gases and are looking for

  • a PhD student

If you are interested in working on exotic states of matter and like to setup new things, contact Tilman Pfau via email/phone or just come by and visit our labs.

Interested? Here you find the recent papers on our quantum liquid

M. Schmitt, M. Wenzel, B. Böttcher, I. Ferrier-Barbut, T. Pfau
Self-bound droplets of a dilute magnetic quantum liquid
Nature 539, 259 (2016), arXiv:1607.07355

I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, T. Pfau
"Observation of quantum droplets in a strongly dipolar Bose gas"
Phys. Rev. Lett. 116, 215301 (2016)

Please contact us.

Project Team

Postdoc, Fellow Alexander von Humboldt Foundation
Phone: +49 711 685-64951

Contact

Tilman Pfau
Prof. Dr.

Tilman Pfau

Head of Institute

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