Tim Langen
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View article: High-resolution spectroscopy of barium monofluoride: Odd isotopologues, hyperfine structure, and isotope shifts
High-resolution spectroscopy of barium monofluoride: Odd isotopologues, hyperfine structure, and isotope shifts Open
Barium monofluoride (BaF) is a promising molecular species for precision tests of fundamental symmetries and interactions. We present a combined theoretical and experimental study of BaF spectra and isotope shifts, focusing in particular o…
View article: Self-Bound Superfluid Membranes and Monolayer Crystals of Ultracold Polar Molecules
Self-Bound Superfluid Membranes and Monolayer Crystals of Ultracold Polar Molecules Open
We investigate the physics of ultracold dipolar molecules using path-integral quantum Monte Carlo simulations, and construct the complete phase diagram extending from weak to strong interactions and from small to mesoscopic particle number…
View article: Magnetic hyperfine structure constants of $^{137}$BaF in the $^2Π_{1/2}$ and $^2Π_{3/2}$ excited states
Magnetic hyperfine structure constants of $^{137}$BaF in the $^2Π_{1/2}$ and $^2Π_{3/2}$ excited states Open
High-precision molecular experiments testing the Standard Model of particle physics require an accurate understanding of the molecular structure at the hyperfine level, both for the control of the molecules and for the interpretation of th…
View article: Laser-cooled <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>BaF</mml:mi><mml:mprescripts/><mml:none/><mml:mn>137</mml:mn></mml:mmultiscripts></mml:math> molecules for measuring nuclear-spin-dependent parity violation
Laser-cooled molecules for measuring nuclear-spin-dependent parity violation Open
We demonstrate optical cycling and transverse laser cooling of a beam of fermionic BaF137 molecules. Their high masses and nuclear spins make these molecules sensitive probes for parity violation and properties of the weak interaction. How…
View article: Molecular laser cooling using serrodynes: implementation, characterization and prospects
Molecular laser cooling using serrodynes: implementation, characterization and prospects Open
An important effort is currently underway to extend optical cycling and laser cooling to more molecular species. Significant challenges arise in particular when multiple nuclear spins give rise to complex, resolved hyperfine spectra, as is…
View article: Self-bound monolayer crystals of ultracold polar molecules
Self-bound monolayer crystals of ultracold polar molecules Open
We investigate the physics of ultracold dipolar molecules using path-integral quantum Monte Carlo simulations, and construct the complete phase diagram extending from weak to strong interactions and from small to mesoscopic particle number…
View article: Dipolar Droplets of Strongly Interacting Molecules
Dipolar Droplets of Strongly Interacting Molecules Open
We simulate a molecular Bose-Einstein condensate in the strongly dipolar regime, observing the existence of self-bound droplets, as well as their splitting into multiple droplets by confinement-induced frustration. Our quantum Monte Carlo …
View article: Laser cooled 137BaF molecules for measuring nuclear-spin-dependent parity violation
Laser cooled 137BaF molecules for measuring nuclear-spin-dependent parity violation Open
We demonstrate optical cycling and transverse laser cooling of a beam of fermionic 137BaF molecules. Their high masses and nuclear spins make these molecules sensitive probes for parity violation and properties of the weak interaction. How…
View article: Molecular laser cooling using serrodynes: Implementation, characterization and prospects
Molecular laser cooling using serrodynes: Implementation, characterization and prospects Open
An important effort is currently underway to extend optical cycling and laser cooling to more molecular species. Significant challenges arise in particular when multiple nuclear spins give rise to complex, resolved hyperfine spectra, as is…
View article: Isotopologue-selective laser cooling of molecules
Isotopologue-selective laser cooling of molecules Open
Direct laser cooling of molecules has made significant progress in recent years. However, the selective cooling and manipulation of generic molecular samples based on their isotopic composition, which is ubiquitous in atomic laser cooling,…
View article: Laser cooling of barium monofluoride molecules using synthesized optical spectra
Laser cooling of barium monofluoride molecules using synthesized optical spectra Open
We demonstrate laser cooling of barium monofluoride (BaF138) molecules. We use serrodynes to synthesize time-sequenced optical spectra that can be precisely tailored to the hyperfine structure of this heaviest nonradioactive alkaline earth…
View article: Dipolar droplets of strongly interacting molecules
Dipolar droplets of strongly interacting molecules Open
We simulate a molecular Bose-Einstein condensate in the strongly dipolar regime, observing the existence of self-bound droplets, as well as their splitting into multiple droplets by confinement-induced frustration. Our quantum Monte Carlo …
View article: Isotopologue-selective laser cooling of molecules
Isotopologue-selective laser cooling of molecules Open
Direct laser cooling of molecules has made significant progress in recent years. However, the selective cooling and manipulation of molecules based on their isotopic composition, which is ubiquitous in atomic laser cooling, has not yet bee…
View article: Laser cooling of barium monofluoride molecules using synthesized optical spectra
Laser cooling of barium monofluoride molecules using synthesized optical spectra Open
We demonstrate laser cooling of barium monofluoride (138BaF) molecules. We use serrodynes to synthesize time-sequenced optical spectra that can be precisely tailored to the hyperfine structure of this heaviest non-radioactive alkaline eart…
View article: Self-organization in the avalanche, quench and dissipation of a molecular ultracold plasma
Self-organization in the avalanche, quench and dissipation of a molecular ultracold plasma Open
Spontaneous avalanche to plasma begins in the core of an ellipsoidal Rydberg gas of nitric oxide. Ambipolar expansion of NO $^+$ draws energy from avalanche-heated electrons. Then, cycles of long-range resonant electron transfer from Rydbe…
View article: Absorption spectroscopy for laser cooling and high-fidelity detection of barium monofluoride molecules
Absorption spectroscopy for laser cooling and high-fidelity detection of barium monofluoride molecules Open
Currently, there is great interest in laser cooling of barium monofluoride (BaF) molecules for precision tests of fundamental symmetries. We use high-resolution absorption spectroscopy to characterize several as yet imprecisely known trans…
View article: A scalable scanning transfer cavity laser stabilization scheme based on the Red Pitaya STEMlab platform
A scalable scanning transfer cavity laser stabilization scheme based on the Red Pitaya STEMlab platform Open
Many experiments in atomic and molecular physics require simultaneous frequency stabilization of multiple lasers. We present a stabilization scheme based on a scanning transfer cavity lock that is simple, stable and easily scalable to many…
View article: Quantum state manipulation and cooling of ultracold molecules
Quantum state manipulation and cooling of ultracold molecules Open
An increasingly large variety of molecular species are being cooled down to low energies in recent years, and innovative ideas and powerful techniques continue to emerge to gain ever more precise control of molecular motion. In this brief …
View article: Microscopic 3D printed optical tweezers for atomic quantum technology
Microscopic 3D printed optical tweezers for atomic quantum technology Open
Trapping of single ultracold atoms is an important tool for applications ranging from quantum computation and communication to sensing. However, most experimental setups, while very precise and versatile, can only be operated in specialize…
View article: Self-bound dipolar droplets and supersolids in molecular Bose-Einstein condensates
Self-bound dipolar droplets and supersolids in molecular Bose-Einstein condensates Open
We numerically study the many-body physics of molecular Bose-Einstein\ncondensates with strong dipole-dipole interactions. We observe the formation of\nself-bound droplets, and explore phase diagrams that feature a variety of\nexotic super…
View article: Supersolidity in Two-Dimensional Trapped Dipolar Droplet Arrays
Supersolidity in Two-Dimensional Trapped Dipolar Droplet Arrays Open
We theoretically investigate the ground states and the spectrum of elementary excitations across the superfluid to droplet crystallization transition of an oblate dipolar Bose-Einstein condensate. We systematically identify regimes where s…
View article: Roton Excitations in an Oblate Dipolar Quantum Gas
Roton Excitations in an Oblate Dipolar Quantum Gas Open
We observe signatures of radial and angular roton excitations around a droplet crystallization transition in dipolar Bose-Einstein condensates. In situ measurements are used to characterize the density fluctuations near this transition. Th…
View article: Density Fluctuations across the Superfluid-Supersolid Phase Transition in a Dipolar Quantum Gas
Density Fluctuations across the Superfluid-Supersolid Phase Transition in a Dipolar Quantum Gas Open
Phase transitions share the universal feature of enhanced fluctuations near\nthe transition point. Here we show that density fluctuations reveal how a\nBose-Einstein condensate of dipolar atoms spontaneously breaks its translation\nsymmetr…
View article: Buffer-gas cooling, high-resolution spectroscopy, and optical cycling of barium monofluoride molecules
Buffer-gas cooling, high-resolution spectroscopy, and optical cycling of barium monofluoride molecules Open
We demonstrate buffer-gas cooling, high-resolution spectroscopy and cycling\nfluorescence of cold barium monofluoride (BaF) molecules. Our source produces\nan intense and internally cold molecular beam containing the different BaF\nisotopo…
View article: Fate of the Amplitude Mode in a Trapped Dipolar Supersolid
Fate of the Amplitude Mode in a Trapped Dipolar Supersolid Open
We theoretically investigate the spectrum of elementary excitations of a trapped dipolar quantum gas across the BEC-supersolid phase transition. Our calculations reveal the existence of distinct Higgs amplitude and Nambu-Goldstone modes th…
View article: Transient Supersolid Properties in an Array of Dipolar Quantum Droplets
Transient Supersolid Properties in an Array of Dipolar Quantum Droplets Open
We study theoretically and experimentally the emergence of supersolid\nproperties in a dipolar Bose-Einstein condensate. The theory reveals a ground\nstate phase diagram with three distinct regimes - a regular Bose-Einstein\ncondensate, in…
View article: Dilute dipolar quantum droplets beyond the extended Gross-Pitaevskii equation
Dilute dipolar quantum droplets beyond the extended Gross-Pitaevskii equation Open
Dipolar quantum droplets are exotic quantum objects that are self-bound due to the subtle balance of attraction, repulsion, and quantum correlations. Here we present a systematic study of the critical atom number of these self-bound drople…