Nonadiabatic transitions in electrostatically trapped ammonia molecules

Nonadiabatic transitions are known to be major loss channels for atoms in magnetic traps but have thus far not been experimentally reported upon for trapped molecules. We have observed and quantified losses due to nonadiabatic transitions for three isotopologues of ammonia in electrostatic traps by comparing the trapping times in traps with a zero and a nonzero electric field at the center. Nonadiabatic transitions are seen to dominate the overall loss rate even for the present samples that are at relatively high temperatures of 30 mK. It is anticipated that losses due to nonadiabatic transitions in electric fields are omnipresent in ongoing experiments on cold molecules.

Figure 1

(Color online) (a) Energy of the $|J,K⟩=|1,1⟩$ level of ${{}^{14}\text{N}\text{H}}_3$ (dashed line) and ${{}^{14}\text{N}\text{D}}_3$ (straight line) in fields up to 150 kV/cm. In panel (b), (c), and (d) the Stark shift of the upper inversion doublet hyperfine components in low electric fields is shown on expanded scales for ${{}^{14}\text{N}\text{H}}_3$, ${{}^{14}\text{N}\text{D}}_3$, and ${{}^{15}\text{N}\text{D}}_3$, respectively. For the calculation of the electric field dependence of the hyperfine components, see Ref. [22]. The $v/x$ curves indicate the rate of change in the direction of the electric field for a molecule with velocity $v$ (1 and 10 m/s) passing the trap center at a distance $x$ (upper axis).

Figure 2

(Color online) Scheme of the experimental setup, with an expanded view of the IP-type electrostatic trap. The voltages applied to the six cylindrical electrodes are shown (b), together with the resulting potential energies for ${\text{NH}}_3$ (dashed line) and ${\text{ND}}_3$ (straight line) along a line in the horizontal symmetry plane for a nonzero (top) and a zero (bottom) electric field at the trap center (c).

Figure 3

(Color online) (a) Lifetime measurements for ${{}^{14}\text{N}\text{D}}_3$ in the two trap configurations, both on a linear and on a logarithmic scale (inset). In the inset, straight lines are included to guide the eyes. (b) Lifetime measurements for ${{}^{15}\text{N}\text{D}}_3$ with original $\left(V_{D/Q}\right)$ and reduced $\left(V_{D/Q}/4\right)$ trap voltages on a logarithmic scale. The measurements have been performed with intervals of 20 ms and with 16 averages per time point. The nonzero field in the trap center is 16 kV/cm for all measurements shown.