Ultracold⁸⁸Sr₂molecules in the absolute ground state

New Horizons: Scalar and Vector Ultralight Dark Matter

“…An initial demonstration of a vibrational molecular clock based on Sr 2 molecules at microkelvin temperatures yielded spectroscopic quality factors approaching 10 12 , with molecule-light coherence times of ∼ 100 ms [319,338]. The possibility to probe vibrational states across the entire groundstate electronic potential [339] can allow one to use molecular clock transitions with different sensitivities to µ-variations in a self-referenced configurations. This success opens the door to tighter constraints on µ-variations than what was previously achieved with molecular systems.…”

Quantum control of molecules for fundamental physics

“…The tried and true approach involves associating ultracold atoms into molecules using photoassociation [13][14][15][16][17][18][19][20][21] or magnetic Feshbach resonances [22][23][24][25]. The latter is largely applicable to alkali-metal dimers (e.g., KRb [26]), while the former can work well for nonmagnetic alkalineearth-metal dimers (e.g., Sr 2 [19]).…”

“…For neutral species, spectroscopy in the Lamb-Dicke and resolved sideband regime has been demonstrated in ultracold Sr 2 molecules trapped in an optical lattice (a trapping potential from a standing wave of laser light). By probing along the axis of tight confinement, the Lamb-Dicke condition is satisfied for optical transition frequencies of ∼500 THz [110], and even more so for Raman rovibrational transitions with frequencies of ∼100 MHz to 30 THz driven by co-propagating probe lasers [20,111,112]. While this is a reliable method to achieve Doppler-free spectroscopy, the technical requirements are fairly stringent.…”

“…This has been achieved for frequency-comb driven Raman rotational transitions in single CaH + ions [113], direct rotational transitions in HD + ion ensembles [114], direct mid-infrared vibrational spectroscopy of HD + ensembles [45,115], and two-photon vibrational transitions in HD + To detect the transferred molecules, the STIRAP sequence is reversed as shown. Adapted from [20]. (b) Rabi oscillations across nearly the entirety of the X 1 Σ + g ground potential achieved by tuning the optical lattice to a magic wavelength for the vibrational clock states.…”

“…They are photoassociated from Sr atoms that are easily laser-cooled to just ∼ 1 µK [19]. Moreover, these molecules have been efficiently created in weakly bound and deeply bound vibrational states [20], and are amenable to atomic-clock level metrological preci-sion [111,112]. Ultrahigh-precision vibrational spectra of these molecules can be initially studied via King plot analysis methods in combination with state-of-the-art theory that is actively under development.…”