Optical trapping of a polyatomic molecule

Abstract

We report optical trapping of a polyatomic molecule, calcium monohydroxide (CaOH). CaOH molecules from a magneto-optical trap are sub-Doppler laser cooled to 20(3) µK in free space and loaded into an optical dipole trap. We attain an in-trap molecule number density of 3(1) × 10 9 cm −3 at a temperature of 57(8) µK. Trapped CaOH molecules are optically pumped into an excited vibrational bending mode, whose -type parity doublet structure is a potential resource for a wide range of proposed quantum science applications with polyatomic molecules. We measure the spontaneous, radiative lifetime of this bending mode state to be ∼0.7 s.

Toward improved loading, cooling, and trapping of molecules in magneto-optical traps

“…Although the achievable temperature in the compressed redMOT is still somewhat high, nearly all molecules from a 'Test 1' redMOT can be recaptured when switching to either a 'Test 1' or 'Test 2' blueMOT. Recently, an rf-redMOT of CaOH at a similar gradient to that simulated here was demonstrated to yield a molecular cloud size of 800 µm [5]; 1% of the molecules in this MOT could then be transferred into an ODT [17]. Implementing a subsequent blueMOT, thus shrinking the cloud size to ∼200 µm, should increase the density by a factor of ∼50, and thus dramatically improve ODT loading fraction, just as discussed in section 5 for the case of SrF.…”

“…by inelastic collisions [21,22,91], phase noise-induced transitions from the microwave shielding [20,23] used to avoid said inelastic collisions [92,93], and black-body radiation induced vibrational transitions [24]. Achieving quantum degeneracy in directly cooled molecules will increase the chemical diversity of quantum degenerate molecular systems dramatically; benefits include the additional spin degree of freedom afforded by the unpaired spin in 2 Σ molecules [94], the ability to study a more diverse range of quantum chemical reactions [95], the potential for quantum degenerate gases of triatomic [5,17] or even polyatomic [96,97] laser coolable molecules, and advantages for precision measurements [98][99][100][101].…”

“…Since the blueMOT reduces σ from 1 mm to ∼100 µm, the density would be increased by ∼10 3 relative to that used in current experiments [2,3,16,67,78]. Typically, experiments load an ODT by turning off the compressed MOT, then turning on Λ-enhanced gray molasses cooling [13][14][15][16][17] along with the ODT for loading. With this protocol, the ODT capture fraction is roughly proportional to the number of molecules originally within the ODT beam diameter (typically 100 µm or less); using a blueMOT should enable near unit efficiency for molecules from the MOT being captured in the ODT, compared to the current state of the art of <5% [14].…”

“…We next applied the generalized code to molecules with minimal hyperfine structure. The alkaline earth hydroxides CaOH and SrOH have both been laser-cooled [80,81]; additionally, CaOH has been trapped in an rf-redMOT [5] and subsequently optically trapped [17]. Here, we perform simulations of effective dc-redMOTs and dc-blueMOTs of both molecules.…”

“…Denser MOTs with higher molecule number would be especially beneficial for experiments seeking to subsequently load into optical dipole traps (ODTs) [13][14][15][16][17] for the purpose of evaporative cooling to quantum degeneracy. Such cooling has recently been demonstrated in ultracold assembled bi-alkali molecules [18][19][20], but is yet to be achieved for directly laser-cooled molecules.…”