Modeling the adiabatic creation of ultracold polar 23Na40K molecules

Abstract

In this work we model and realize stimulated Raman adiabatic passage (STIRAP) in the diatomic 23 Na 40 K molecule from weakly bound Feshbach molecules to the rovibronic ground state via the |v d = 5, J = Ω = 1 excited state in the d 3 Π electronic potential. We demonstrate how to set up a quantitative model for polar molecule production by taking into account the rich internal structure of the molecules and the coupling laser phase noise. We find excellent agreement between the model predictions and the experiment, demonstrating the applicability of the model in the search of an ideal STIRAP transfer path. In total we produce 5000 fermionic groundstate molecules. The typical phase-space density of the sample is 0.03 and induced dipole moments of up to 0.54 Debye could be observed.Dipolar quantum gases allow for the realization of intriguing new quantum many-body systems and associated phenomena due to their anisotropic and long-range interactions. Among these are the roton driven fluid to crystalline quantum phase transition [1], dipolar droplet formation [2,3], insulators with fractional filling and supersolid phases of dipoles in optical lattices [4] to name only a few. Ultracold polar molecules promise particularly large dipolar interactions due to their large dipole moments.The standard procedure for creating molecules at high phase-space density starts with a mixture of two atomic species close to quantum degeneracy. The two species are then initially adiabatically associated into a weakly bound Feshbach molecular state |F B [5]. From there they can be transferred into the final, electronic, vibrational and rotational (rovibronic) ground state using stimulated Raman adiabatic passage (STIRAP) [6,7]. This last step involves coupling the initial and final state to a common intermediate, electronically excited molecular state. Both |F B and the intermediate state need to be chosen with care in order to allow for a high efficiency in the transfer and thus to preserve the phase space density of the ultracold mixture. This approach has been applied successfully to dipolar KRb [8] to the ground state compared to the STIRAP scheme employed in [11]. We develop a Hamiltonian model to describe the adiabatic transfer in all required details to achieve a quantitative description. In addition to the molecular structure analysis done for different bialkali systems [14,15] we include the complex light coupling into the analysis. This results in a multi-level, crosscoupled model that is intimately related to the work of the Bergmann group on STIRAP in multilevel systems [16] but is specific to the alkali-alkali molecule formation. We investigate how to maximize the STIRAP transfer efficiency for a given intermediate state manifold by optimizing pulse durations and one-photon detuning. We find excellent agreement between simulation and experiment. Finally, we demonstrate ground state molecule creation with a large electric dipole moment of up to 0.54 Debye. I. MOLECULAR LEVEL STRUCTURE AND HAMILTONIAN MODELIn our model we us...

Ultracold polar molecules as qudits

“…Molecules in 2 Σ states possess an unpaired electron, whereas those in 1 Σ states do not. 1 Σ is the electronic ground state of molecules formed by associating two alkali atoms [39][40][41][42][43][44][45][46][47][48][49]. S 2 is the electronic ground state of molecules such as SrF [50], CaF [51,52], YbF [78] and YO [53], which have been recently laser cooled.…”

“…The rotational and spin degrees of freedom make it possible to encode quantum information in ways not possible on other platforms. Experiments with ultracold molecules have progressed rapidly over the last decade [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53], and the rotational, fine and hyperfine structure has been studied in detail [54][55][56][57][58][59][60][61]. Heteronuclear molecules can have electric dipole moments fixed in the molecular frame, allowing manipulation of the quantum states with microwave fields [57][58][59]62].…”

Quasiclassical method for calculating the density of states of ultracold collision complexes

“…where r ij indicates the distance between atom i and j. Atoms 1 and 2 are the K-atoms and atoms 3 and 4 are the Na-atoms and W 2 ≡ W (u 2 , 1/2, 1/16) with u 2 = r 23 + r 14 r 13 + r 24 + r 23 + r 14 .…”

Extending Rotational Coherence of Interacting Polar Molecules in a Spin-Decoupled Magic Trap

“…We observe density-dependent coherence times, which can be explained by dipolar interactions in the bulk gas.Interacting particles with long coherence times are a key ingredient for entanglement generation and quantum engineering. Cold and ultracold polar molecules [1][2][3][4][5][6][7][8][9][10][11] are promising systems for exploring such quantum manybody physics with long-range interactions [12,13] due to their strong and tunable electric dipole moment and long single-particle lifetime [14,15]. The manipulation of their rich internal degrees of freedom has been studied for different molecular species [16][17][18][19].…”