Observation of Bose-Einstein Condensation of Dipolar Molecules (2312.10965v1)

Abstract: Ensembles of particles governed by quantum mechanical laws exhibit fascinating emergent behavior. Atomic quantum gases, liquid helium, and electrons in quantum materials all show distinct properties due to their composition and interactions. Quantum degenerate samples of bosonic dipolar molecules promise the realization of novel phases of matter with tunable dipolar interactions and new avenues for quantum simulation and quantum computation. However, rapid losses, even when reduced through collisional shielding techniques, have so far prevented cooling to a Bose-Einstein condensate (BEC). In this work, we report on the realization of a BEC of dipolar molecules. By strongly suppressing two- and three-body losses via enhanced collisional shielding, we evaporatively cool sodium-cesium (NaCs) molecules to quantum degeneracy. The BEC reveals itself via a bimodal distribution and a phase-space-density exceeding one. BECs with a condensate fraction of 60(10) % and a temperature of 6(2) nK are created and found to be stable with a lifetime close to 2 seconds. This work opens the door to the exploration of dipolar quantum matter in regimes that have been inaccessible so far, promising the creation of exotic dipolar droplets, self-organized crystal phases, and dipolar spin liquids in optical lattices.

• The paper achieved quantum degeneracy in NaCs molecules with a 60% condensate fraction at 6 nK through optimized evaporative cooling.
• The paper utilized circular and linear polarized microwave fields to dress molecules, effectively suppressing two- and three-body collision losses.
• The paper’s findings open new avenues for exploring exotic dipolar quantum phases and simulating complex many-body systems.

Observation of Bose-Einstein Condensation of Dipolar Molecules

The paper under review outlines a significant advancement in the paper of quantum degenerate gases, particularly focusing on the realization of Bose-Einstein condensation (BEC) in dipolar molecules. This achievement marks a substantial extension of control over quantum matter, previously limited to atomic BECs and magnetic atoms, to complex molecules with long-range interactions.

The authors have successfully cooled sodium-cesium (NaCs) dipolar molecules to quantum degeneracy, achieving a BEC with a condensate fraction of 60% and a temperature of 6 nK. These molecules display strong dipole-dipole interactions which, under normal circumstances, lead to rapid losses and pose challenges to achieving BEC. The paper circumvents these challenges by employing enhanced collisional shielding, significantly suppressing two- and three-body losses. This is accomplished by using a combination of circular ($\sigma^+$) and linear ($\pi$) polarized microwave fields to dress the molecules, thereby creating a robust evaporation path to BEC.

The experimental setup involved starting with an ensemble of NaCs molecules, prepared through stimulated Raman adiabatic passage into their absolute ground state. By adjusting the microwave parameters—specifically the Rabi frequencies and detunings—the paper reports an efficient evaporative cooling process leading to BEC. During this process, the peak density remained stable at approximately 1.5-2.0 x 10^12 cm^-3, indicative of a weakly interacting Bose gas where quantum depletion is negligible, owing to the control over the s-wave scattering length and dipolar interactions.

The implications of this research are substantial. The creation of a molecular BEC opens avenues for exploring exotic dipolar quantum phases, such as dipolar droplets and self-organized structures in both two and three dimensions. The ability to tune dipole-dipole interactions holds promise for studies in supersolid behavior, 2D dipolar crystals, and novel quantum magnetism. Furthermore, loading such a BEC into optical lattices could facilitate the exploration of Hubbard models with dipolar interactions, enabling investigations into Mott insulators, fractional filling, and potential pathways to realizing quantum spin liquids.

A noteworthy aspect of this paper is its detailed investigation of the role of intermolecular potentials, demonstrating how the modification of the long-range interaction landscape through microwave dressing can mitigate loss mechanisms and stabilize quantum phases of matter that were previously inaccessible. This control over molecular interactions aligns with theoretical frameworks predicting strongly correlated matter phases, and it establishes dipolar molecules as a robust platform for quantum simulation and potential quantum computing applications.

In conclusion, this work demonstrates not only the achievement of BEC in a previously daunting system of dipolar molecules but also highlights the potential of these systems in enriching the landscape of quantum many-body physics and simulations. The comprehensive methodology, coupled with the robust numerical results, paves the way for further explorations into complex dipolar systems and their myriad applications in advancing our understanding of quantum mechanics.