Sticky collisions of ultracold RbCs molecules

Abstract

Understanding and controlling collisions is crucial to the burgeoning field of ultracold molecules. All experiments so far have observed fast loss of molecules from the trap. However, the dominant mechanism for collisional loss is not well understood when there are no allowed 2-body loss processes. Here we experimentally investigate collisional losses of nonreactive ultracold 87 Rb 133 Cs molecules, and compare our findings with the sticky collision hypothesis that pairs of molecules form long-lived collision complexes. We demonstrate that loss of molecules occupying their rotational and hyperfine ground state is best described by second-order rate equations, consistent with the expectation for complex-mediated collisions, but that the rate is lower than the limit of universal loss. The loss is insensitive to magnetic field but increases for excited rotational states. We demonstrate that dipolar effects lead to significantly faster loss for an incoherent mixture of rotational states.

Controlling the ac Stark effect of RbCs with dc electric and magnetic fields

“…The transitions to vibronic levels of the b 3 state in this wavelength range are suppressed by negligible Franck-Condon factors [78,101]. Nevertheless, during initial attempts to load RbCs molecules into an ODT of λ ≈ 1064 nm, we observed a loss of groundstate molecules that was orders of magnitude faster than the near-universal collisional losses that typically dominate our experiments [102,103].…”

Photoinduced Two-Body Loss of Ultracold Molecules

“…Rb 133 Cs [15,16], 23 Na 87 Rb [17], and the fermionic 23 Na 40 K [18,19]. However, losses were still observed at about the same rate that would be expected of reactive molecules [20][21][22]. In all of these experiments, the lifetime of the gas in the crossed optical dipole trap was limited to a few seconds [18] or less [15][16][17].…”

“…Hence, essentially all complexes formed undergo laser excitation before they dissociate, such that complex formation manifests as effective two-body loss, in agreement with experimental observations in Refs. [15,16,18,20,22]. Switching to a 10 μm laser wavelength would reduce the excitation rate by orders of magnitude to around 0.2 ms −1 , which is much slower than the complex dissociation rate.…”

Robust entangling gate for polar molecules using magnetic and microwave fields

“…For concreteness, we illustrate our discussion with numerical results for CaF (X 2 ), which has been laser cooled to temperatures below 10 μK [5,[8][9][10]31,49]. Our proposal is also applicable to bialkali-metal molecules in their lowest 1 or 3 states; to illustrate this, we present in Appendix D analogous numerical results for RbCs [3,16,[50][51][52][53].…”

“…The field of ultracold molecules has seen enormous progress in the past few years, with landmark achievements such as the production of the first quantum-degenerate molecular Fermi gas [1], low-entropy molecular samples in optical lattices [2,3], trapping of single molecules in optical tweezers [4][5][6], and magneto-optical trapping and sub-Doppler cooling of molecules [7][8][9][10][11]. These results bring significantly closer a broad range of applications of ultracold molecules, from state-controlled chemistry [12][13][14][15][16][17] and novel tests of fundamental laws of nature [18][19][20][21] to new architectures for quantum computation [22][23][24][25][26], quantum simulation [27][28][29][30][31][32], and quantum sensing [33,34].…”