Quantum fluctuations in dipolar gases: Quantum droplets, vortices and impurities

• Applicant: Professor Dr. Tilman Pfau
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392530138

• Final Report Year: 2022

Final Report Abstract

In conclusion, within this DFG project we studied novel quantum phases of ultracold dipolar quantum gases. The complex interplay of anisotropic dipolar interactions, quantum fluctuations, and the trap geometries lead to a range of intriguing quantum phases. In addition to self-bound quantum liquids, we were able to prepare and study one- and twodimensional arrays of quantum droplets, which form via a modulation instability driven by roton-like excitations at finite wave vectors, and ultimately also a supersolid state of matter which features both diagonal and off-diagonal order. We used our high-resolution in situ imaging in combination with time of flight techniques to study real and momentum space density profile, as well as density fluctuations on top of the mean density. Together with the exquisite control over the (trap) geometry of the system and the magnitude and orientation of the dipole polarization direction, this allowed us to study density modulations, phase coherences as well as the defining low-lying collective excitations of the different quantum phases. In addition to the experimental studies, a theoretical framework, in particular applying an extended Gross-Pitaevskii formalism was developed and refined. Crucially, within this framework quantum fluctuations are taken into account to first order by an addition nonlinear term. We successfully used the eGPE to develop a deep understanding of the experimentally observed phases and their fundamental excitations, but also to predict a whole range of different supersolid and superglass morphologies for higher atom number in oblate trap geometries.

Publications

• Ultrakalt Magnetisiert, Physik Journal 17, 35 (2018)
  T. Langen & Manfred J. Mark
  
• Dilute dipolar quantum droplets beyond the extended Gross-Pitaevskii equation. Physical Review Research, 1(3).
  Böttcher, Fabian; Wenzel, Matthias; Schmidt, Jan-Niklas; Guo, Mingyang; Langen, Tim; Ferrier-Barbut, Igor; Pfau, Tilman; Bombín, Raúl; Sánchez-Baena, Joan; Boronat, Jordi & Mazzanti, Ferran
  
• Fate of the Amplitude Mode in a Trapped Dipolar Supersolid. Physical Review Letters, 123(19).
  Hertkorn, J.; Böttcher, F.; Guo, M.; Schmidt, J. N.; Langen, T.; Büchler, H. P. & Pfau, T.
  
• The low-energy Goldstone mode in a trapped dipolar supersolid. Nature, 574(7778), 386-389.
  Guo, Mingyang; Böttcher, Fabian; Hertkorn, Jens; Schmidt, Jan-Niklas; Wenzel, Matthias; Büchler, Hans Peter; Langen, Tim & Pfau, Tilman
  
• Transient Supersolid Properties in an Array of Dipolar Quantum Droplets. Physical Review X, 9(1).
  Böttcher, Fabian; Schmidt, Jan-Niklas; Wenzel, Matthias; Hertkorn, Jens; Guo, Mingyang; Langen, Tim & Pfau, Tilman
  
• New states of matter with fine-tuned interactions: quantum droplets and dipolar supersolids. Reports on Progress in Physics, 84(1), 012403.
  Böttcher, Fabian; Schmidt, Jan-Niklas; Hertkorn, Jens; Ng, Kevin S. H.; Graham, Sean D.; Guo, Mingyang; Langen, Tim & Pfau, Tilman
  
• Density Fluctuations across the Superfluid-Supersolid Phase Transition in a Dipolar Quantum Gas. Physical Review X, 11(1).
  Hertkorn, J.; Schmidt, J.-N.; Böttcher, F.; Guo, M.; Schmidt, M.; Ng, K. S. H.; Graham, S. D.; Büchler, H. P.; Langen, T.; Zwierlein, M. & Pfau, T.
  
• Pattern formation in quantum ferrofluids: From supersolids to superglasses. Physical Review Research, 3(3).
  Hertkorn, J.; Schmidt, J.-N.; Guo, M.; Böttcher, F.; Ng, K. S. H.; Graham, S. D.; Uerlings, P.; Langen, T.; Zwierlein, M. & Pfau, T.
  
• Roton Excitations in an Oblate Dipolar Quantum Gas. Physical Review Letters, 126(19).
  Schmidt, J.-N.; Hertkorn, J.; Guo, M.; Böttcher, F.; Schmidt, M.; Ng, K. S. H.; Graham, S. D.; Langen, T.; Zwierlein, M. & Pfau, T.
  
• Supersolidity in Two-Dimensional Trapped Dipolar Droplet Arrays. Physical Review Letters, 127(15).
  Hertkorn, J.; Schmidt, J.-N.; Guo, M.; Böttcher, F.; Ng, K. S. H.; Graham, S. D.; Uerlings, P.; Büchler, H. P.; Langen, T.; Zwierlein, M. & Pfau, T.
  
• Dipolar supersolids: Solid and superfluid at the same time. Physics Today, 75(3), 36-41.
  Langen, Tim
  
• Topological Quantum Critical Points in the Extended Bose-Hubbard Model. Physical Review Letters, 128(4).
  Fraxanet, Joana; González-Cuadra, Daniel; Pfau, Tilman; Lewenstein, Maciej; Langen, Tim & Barbiero, Luca