Quantum Engineering of a Low-Entropy Gas of Heteronuclear Bosonic Molecules in an Optical Lattice

Abstract

We demonstrate a generally applicable technique for mixing two-species quantum degenerate bosonic samples in the presence of an optical lattice, and we employ it to produce low-entropy samples of ultracold 87 Rb 133 Cs Feshbach molecules with a lattice filling fraction exceeding 30%. Starting from two spatially separated Bose-Einstein condensates of Rb and Cs atoms, Rb-Cs atom pairs are efficiently produced by using the superfluid-to-Mott insulator quantum phase transition twice, first for the Cs sample, then for the Rb sample, after nulling the Rb-Cs interaction at a Feshbach resonance's zero crossing. We form molecules out of atom pairs and characterize the mixing process in terms of sample overlap and mixing speed. The dense and ultracold sample of more than 5000 RbCs molecules is an ideal starting point for experiments in the context of quantum many-body physics with long-range dipolar interactions.PACS numbers: 05.30. Rt, 37.10.Jk, Samples of dipolar ground-state molecules with low entropy offer a platform for exploring new areas of quantum many-body physics and related fields. Because of their long-range, spatially anisotropic interaction they have been proposed to enable investigations into novel forms of quantum matter, e.g., supersolidity, unconventional manifestations of superfluidity, and novel types of quantum magnetism [1][2][3]. They are expected to allow the realization of many-body spin systems [4] with, in principle, local spin control and readout. In particular, they promise the study of dynamical processes in such systems, e.g., on many-body spin transport and inhibition thereof [5]. In addition, with the exquisite control over all quantum degrees of freedom, they offer the possibility of implementing quantum simulation protocols [6] that require genuine and strong long-range interactions.The production of low-entropy samples of rovibronic ground-state molecules is challenging. To date, the regime of nanokelvin molecular temperatures has only been reached for a selected class of dimer molecules by combining the technique of Feshbach association in ultracold, nearly quantum degenerate, atomic samples with the technique of stimulated ground-state transfer (stimulated Raman adiabatic passage, STIRAP) as pioneered on homonuclear Rb 2 and Cs 2 [7-9] and heteronuclear fermionic KRb [10]. This strategy has recently been applied to various other heteronuclear alkali combinations, i.e., to bosonic RbCs [11, 12], fermionic NaK [13], and bosonic NaRb [14]. In essence, low entropy is obtained on the atomic samples, and Feshbach association and subsequent STIRAP transfer are aimed at maintaining low entropy. * These authors contributed equally to this work. Mixing the degenerate atomic samples is of crucial importance for our specific purpose to create heteronuclear molecules, as well as for many other applications [15][16][17][18][19][20]. Maintaining low entropy in the course of the mixing process and during the subsequent step of association to molecules poses a great experimental challenge. Ideally,...

Modeling the adiabatic creation of ultracold polar 23Na40K molecules

“…The largest loss in phasespace density occurs in the current setup however already prior to STIRAP due to the low efficiency of Feshbach association. This could be mitigated in an optical lattice [26,27] in the future. Finally we demonstrated that molecules with a dipole moment of 0.54 D can be created in our setup, the most polar diatomic molecular sample so far.…”

New frontiers for quantum gases of polar molecules

“…[83] should be able to significantly increase the filling. Similar recent work created a sample of bosonic RbCs Feshbach molecules, at a lattice filling > 30% [84]. There, the Cs was first localized in the MI phase, the Rb was next translated to overlap with the Cs cloud, the lattice depth was then increased further to localize Rb, and finally…”

“…RbCs Feshbach molecules were created via magnetoassociation, setting the stage to produce groundstate molecules [84].…”

Observation of interspecies Feshbach resonances in an ultracold K39−Cs133 mixture and refinement of interaction potentials

“…Only a comparatively small fraction of atoms could be converted to heteronuclear dimers because in bulk samples the process is limited by atomic three-body recombination and vibrational relaxation in atom-molecule and molecule-molecule collisions. Such losses can be suppressed if the two atomic samples are overlapped in an optical lattice, creating either a Bose-Fermi Mott-band insulator [42] or a Bose-Bose double-species Mott insulator [38]. In both cases reported so far, a Feshbach resonance was exploited in two different ways.…”

“…Second, these molecules are optically transferred into the rovibrational ground state by stimulated Raman adiabatic passage (STIRAP) [26,33,34]. This procedure, which requires precise knowledge of the interand intraspecies scattering properties, has recently led to the production of ultracold and dense samples of heteronuclear molecules such as fermionic KRb [26] and NaK [35] and bosonic RbCs [36][37][38] and NaRb [39] in their rovibrational ground states. The present paper is aimed towards the goal of producing ultracold KCs molecules by similar methods.…”