# Dipolar quantum gases and liquids (Prof. T. Pfau)

- Date: Feb 22, 2018
- Time: 11:00 AM - 12:00 PM (Local Time Germany)
- Speaker: Prof. Tilmann Pfau
- 5th Institute of Physics, Universität Stuttgart
- Host: MPQ, IMPRS-QST

Besides the anisotropy the dipolar interaction is nonlocal and as such allows for self organized structure formation. Candidates for dipolar species are polar molecules, Rydberg atoms and magnetic atoms. More than ten years ago the first dipolar effects in a quantum gas were observed in an ultracold Chromium gas. By the use of a Feshbach resonance a purely dipolar quantum gas was observed three years after [1]. By now dipolar interaction effects have been observed in lattices and also for polar molecules. Recently it became possible to study degenerate gases of lanthanide atoms among which one finds the most magnetic atoms. The recent observation of their collisional properties includes the emergence of quantum chaos and very broad resonances [2,3]. Similar to the Rosensweig instability in classical magnetic ferrofluids self-organized structure formation was expected. In our experiments with quantum gases of Dysprosium atoms we could recently observe the formation of a droplet crystal [4]. In contrast to theoretical mean field based predictions the superfluid droplets did not collapse. We find that this unexpected stability is due to beyond meanfield quantum corrections of the Lee-Huang-Yang type [5,6]. We observe and study self-bound droplets [7] which can interfere with each other. These droplets are 100 million times less dense than liquid helium droplets and open new perspectives as a truly isolated quantum system.

__Reference__:

[1] T. Lahaye, C.
Menotti, L. Santos, M. Lewenstein, and T. Pfau, "The physics of dipolar bosonic quantum gases", Rep.
Prog. Phys. 72, 126401 (2009)

[2] T. Maier, I.
Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Pfau, K.
Jachymski, P. S. Julienne, "Broad Feshbach
resonances in collisions of ultracold Dysprosium atoms", Phys. Rev. A 92, 060702(R) (2015)

[3] T.
Maier, H. Kadau, M. Schmitt, M. Wenzel, I. Ferrier-Barbut, T. Pfau, A. Frisch,
S. Baier, K. Aikawa, L. Chomaz, M. J. Mark, F. Ferlaino, C. Makrides, E.
Tiesinga, A. Petrov, S. Kotochigova, "Emergence
of chaotic scattering in ultracold Er and Dy",
Phys. Rev. X 5, 041029 (2015)

[4] H. Kadau, M.
Schmitt, M. Wenzel, C. Wink, T. Maier, I. Ferrier-Barbut, T. Pfau*"Observing the Rosensweig instability of
a quantum ferrofluid", Nature 530, 194 (2016)[5] T. D. Lee, K. Huang, and C. N. Yang, " Eigenvalues and Eigenfunctions of a Bose System of
Hard Spheres and Its Low-Temperature Properties", Phys. Rev. 106, 1135 (1957). D.S. Petrov, “Quantum
mechanical stabilization of a collapsing Bose–Bose mixture”, Phys. Rev. Lett. 115, 155302 (2015).[6] 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)[7] M.
Schmitt, M. Wenzel, F. Böttcher, I. Ferrier-Barbut, and T. Pfau,
"Self-bound droplets of a dilute magnetic quantum liquid", Nature 539, 259 (2016)*