Rotational cooling of molecular ions with 1¿, 2¿, 3¿ and 2¿ electronic ground states

I. S. Vogelius

Brian Odom

Although ion-ion sympathetic cooling is now commonly used to reduce speeds of trapped molecular ions to milliKelvin temperatures, cooling of the decoupled internal molecular modes remains a challenge. Here, we demonstrate that a single spectrally filtered femtosecond laser, tuned to the electronic A-X transition of trapped AlH+, can efficiently cool rotations from room temperature to the ground state. Since this single-laser technique simultaneously drives rotationally de-exciting electronic excitations from all initially populated states, each parity can be cooled as quickly as 100 μs. In our current implementation, full population collection into the N = 0 positive-parity level relies on vibrational relaxation on the timescale of 100 ms. Since this technique cools by step-wise rotational pumping, it is most readily applicable to “alkali-like” molecular species, such as AlH+, with semi-closed cycling transitions. Although we currently use a destructive two-photon state readout technique, these species are also promising candidates for single-molecule fluorescence detection. The ability to quickly cool molecular rotations is expected to be important for precision spectroscopy experiments, quantum information processing applications, and for ultracold chemistry studies.

Peter Frøhlich Staanum, Klaus Højbjerre, Peter Sandegaard Skyt +2 more

Ivan R. Vogelius, Lars Bojer Madsen, Michael Drewsen

The translational motion of molecular ions can be effectively cooled sympathetically to translational temperatures below $100\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ in ion traps through Coulomb interactions with laser-cooled atomic ions. The rovibrational degrees of freedom, however, are expected to be largely unaffected during translational cooling. We have previously proposed schemes for cooling of the internal degrees of freedom of such translationally cold but internally hot heteronuclear diatomic ions in the simplest case of $^{1}\ensuremath{\Sigma}$ electronic ground-state molecules. Here we present a significant simplification of these schemes and make a generalization to the most frequently encountered electronic ground states of heteronuclear molecular ions: $^{1}\ensuremath{\Sigma}$, $^{2}\ensuremath{\Sigma}$, $^{3}\ensuremath{\Sigma}$, and $^{2}\ensuremath{\Pi}$. The schemes are relying on one or two laser-driven transitions with the possible inclusion of a tailored incoherent far-infrared radiation field.

C. H. Raymond Ooi

Christian F. Roos, Dietrich G. Leibfried, Ferdinand Schmidt‐Kaler +2 more