Ultracold Gas of Bosonic Na23K39 Ground-State Mo

Abstract

Ultracold bialkali polar molecules play a leading part at the frontline of quantum physics. They recently attract a lot of attention in the field of ultracold quantum chemistry, quantum many-body physics and quantum simulations. The key for their success is the rich internal level structure with rotational and vibrational degrees of freedom and their large electric dipole moments. Still, only a handful of molecular species are available at ultracold temperatures until now, although it is highly desirable to produce new molecular species to further expand the range of applications. Besides direct laser cooling methods for molecules, the assembly of heteronuclear groundstate molecules from ultracold atomic mixtures is the most promising approach for the creation of polar molecules. It includes the formation of weakly bound Feshbach molecules from the diatomic mixture and the subsequent two-photon stimulated Raman adiabatic passage (STIRAP) transfer to the rovibrational ground state. This creation strategy has been successfully demonstrated for the first time in the pioneering experiments at JILA with ultracold 40 K 87 Rb molecules. Since then, only a few more molecular species from different alkali atoms have been created, namely 6 Li 23 Na, 23 Na 40 K, 23 Na 87 Rb and 87 Rb 133 Cs.In this thesis, I report the successful creation of a new species of ultracold polar ground-state molecules: 23 Na 39 K. Starting from an ultracold mixture of bosonic 23 Na and 39 K atoms, weakly bound molecules are created. For this purpose, a Feshbach resonance in a high angular momentum scattering channel is chosen, experimentally identified and characterized. Close to this resonance the weakly bound Feshbach molecules are formed using resonant radio frequency radiation. For the two-photon ground-state transfer, a unique, highly specialized two-color laser system is designed and realized. It is used for one-and two-photon spectroscopy to identify the relevant transitions for the ground-state transfer. Based on the obtained data, a local model of the singlet-triplet mixed excited state manifolds is developed, with which the hyperfine structure and the magnetic field dependence is predicted with high accuracy. According to these findings, a suitable pathway to a single hyperfine ground state is chosen considering selection rules and experimental conditions such as laser polarization and beam alignment. To precisely determine the two-photon resonance condition for STIRAP, electromagnetically induced transparency measurements are performed. The ground-state transfer is then performed using STIRAP. The experimental findings regarding the STIRAP are successfully supported theoretically by a model based on a five-level master equation. The pure molecular gas shows evidence for two-body dominated loss mechanisms, such as sticky four-body collisions. The molecule-atom mixture of 23 Na 39 K+ 39 K reveals an unexpectedly low loss rate coefficient although sticky three-body collisions are assumed to occur. This behavior demands further investigat...

Coherent manipulation of the internal state of ultracold 87Rb133Cs molecules with multiple microwave fields

“…These properties have led to many proposals for using ultracold polar molecules for quantum computation 1-7 , quantum simulation 8-13 , quantum-state controlled chemistry [14][15][16][17][18][19] , and precision measurement of fundamental constants [20][21][22][23][24][25][26][27][28][29][30] . A number of experiments have successfully generated trapped gases of polar molecules at ultracold temperatures either by association of pre-cooled atomic gases 19,[31][32][33][34][35][36][37][38][39] or by direct laser cooling [40][41][42][43][44][45][46][47][48][49] . Most recently, the former method was used to create the first Fermi-degenerate gas of ultracold polar molecules 50 .The vast majority of the proposed applications of ultracold molecules utilise the rotational and hyperfine degrees of freedom, which together form a large and rich internal space.…”

Roaming pathways and survival probability in real-time collisional dynamics of cold and controlled bialkali molecules

“…The availability of dilute ultracold gases of neutral bialkali molecules in their absolute ground state 1 – 8 and cold diatomic molecular ions 9 – 17 is revolutionizing molecular science. For heteronuclear dimers this stems from their long-range and anisotropic dipole-dipole interactions.…”

“…Other bialkali molecules are chemically stable with respect to molecule-molecule collisions. Examples are bosonic Rb 6 , 35 , K 8 , and Cs 3 , 4 , 36 , and the fermionic K 5 , 7 . Their lifetime in optical traps was expected to be only limited by the rate of collisions with room-temperature molecules in the typical Ultra High Vacuum (UHV) environment used for these experiments and expected to be several seconds.…”

Magic conditions for multiple rotational states of bialkali molecules in optical lattices

“…Proposed applications span the fields of precision measurement and metrology [2][3][4][5][6][7][8], quantum-state resolved chemistry [9][10][11][12][13], dipolar quantum matter [14][15][16][17][18][19], quantum simulation [20][21][22][23][24][25], and quantum information processing [26][27][28][29][30][31][32]. Recent experimental progress on the production of ultracold molecules by association [33][34][35][36][37][38][39][40][41][42][43] and direct laser cooling [44][45][46][47][48][49] has brought many of these applications within reach.…”

“…For diatomic molecules, such as ground-state bialkali molecules [33][34][35][36][37][38][39][40][41][42][43], the dynamic polarizability along the molecular axis (α ) is, in general, different from that perpen-dicular to it (α ⊥ ). For light polarized at an angle θ to the molecular axis, this leads to a dynamic polarizability in the body-fixed frame given by α(θ ) = α (0) + α (2) P 2 (cos(θ )), (1) where α (0) = 1 3 (α + 2α ⊥ ) and α (2) = 2 3 (α − α ⊥ ) are the isotropic and anisotropic components of the polarizability tensor, respectively.…”