Singlet Pathway to the Ground State of Ultracold Polar Molecules

Abstract

Starting from weakly bound Feshbach molecules, we demonstrate a two-photon pathway to the dipolar ground state of bi-alkali molecules that involves only singlet-to-singlet optical transitions. This pathway eliminates the search for a suitable intermediate state with sufficient singlet-triplet mixing and the exploration of its hyperfine structure, as is typical for pathways starting from triplet dominated Feshbach molecules. By selecting a Feshbach state with a stretched singlet hyperfine component and controlling the polarization of the excitation laser, we assure coupling to only a single hyperfine component of the A 1 Σ + excited potential, even if the hyperfine structure is not resolved. Similarly, we address a stretched hyperfine component of the X 1 Σ + rovibrational ground state, and therefore an ideal three level system is established. We demonstrate this pathway with 6 Li 40 K molecules. By exploring deeply bound states of the A 1 Σ + potential, we are able to obtain large and balanced Rabi frequencies for both transitions. This method can be applied to other molecular species.

Ultracold Gas of Bosonic Na23K39 Ground-State Mo

“…For heteronuclear bialkali molecules there are ten different molecular species available: LiNa, LiK, LiRb, LiCs, NaK, NaRb, NaCs, KRb, KCs and RbCs, all composed from the 5 different stable alkali metal atomic species; see Fig. 1.1, namely 6,7 Li, 23 Na, 39,40,41 K, 85,87 Rb and 133 Cs. Due to the different isotopes for the alkali metal atoms, some molecules have several isotopologues, which add up to in total 31 different heteronuclear molecules.…”

“…Typically, the spectroscopy is done starting from a Feshbach molecule state, searching for excited states and the ground state by utilizing loss measurements including dark resonance (Autler-Townes) and dark state (electromagnetically induced transparency, EIT) effects. The findings are reported for example for 40 K 87 Rb [49], 23 Na 40 K [82], 23 Na 87 Rb [83,84] and 6 Li 40 K [85]. The excited states are chosen in a way that they provide a decent admixture of singlet and triplet character and therefore offer a good coupling strength to the mainly a 3 Σ + Feshbach molecule state as well as to the pure X 1 Σ + ground state.…”

“…In case of 6 Li 23 Na a strong singlet-triplet coupling in the excited state is not necessary, because the ground-state molecule is prepared in the a 3 Σ + ground state and therefore the STIRAP does not rely on any singlet-triplet bridge. Recently, an alternative, pure singlet pathway for 6 Li 40 K have been discovered [85], which starts from a singlet potential dominated Feshbach resonance making a detailed understanding of the excited states unnecessary. This approach is pioneering in the sense of simplicity for the STIRAP state transfer and may overcome issues like the weak coupling of the Feshbach molecule state to the excited state.…”

“….19. For 816 nm the resulting finesse is 24900(85), for 1146 nm it is 37400(180). Accordingly, the cavity yields linewidths of 60.2(2) kHz for 816 nm and 40.0(2) kHz for 1146 nm.…”

Empirical LiK excited state potentials: connecting short range and near dissociation expansions

“…From our previous high-resolution two-photon spectroscopy of the X 1 S + ground state 43 the depth of the ground state potential was accurately measured as DðX the wavenumber of the D2-potassium atomic transition l D2 = 13042.899700(3) cm À1 is known from literature. 53 Therefore, an improved value for the depth of the excited state potential can be inferred from the measured data as:…”