Observation of microwave shielding of ultracold molecules

Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we used microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probed collisions in three dimensions. The correct combination of microwave frequency and power created an effective repulsive shield, which suppressed the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold polar molecules and evaporative cooling.

An optical tweezer array of ultracold molecules

Ultracold molecules have important applications that range from quantum simulation and computation to precision measurements probing physics beyond the Standard Model. Optical tweezer arrays of laser-cooled molecules, which allow control of individual particles, offer a platform for realizing this full potential. In this work, we report on creating an optical tweezer array of laser-cooled calcium monofluoride molecules. This platform has also allowed us to observe ground-state collisions of laser-cooled molecules both in the presence and absence of near-resonant light.

Formation of calcium monofluoride in graphite furnace molecular absorption spectrometry, part 2: interference mechanisms of chloride, bromide and sulfate salts

In this study, the interference mechanisms of chloride, bromide and sulfate together with sodium in the determination of CaF by high resolution continuum source molecular absorption spectrometry were investigated.

Formation of calcium monofluoride in graphite furnace molecular absorption spectrometry, part I: interference mechanisms of competitive metals Ga, Al, Ba, and Sr

In this study, the formation mechanisms of CaF and the interference mechanisms of Al, Ba, Ga and Sr on the determination of F via CaF were studied.

"Spectrum-only" assignment of core-penetrating and core-nonpenetrating Rydberg states of calcium monofluoride

Rydberg states of calcium monofluoride in the n* = 17–20 region have been observed by ionization-detected optical–optical double-resonance spectroscopy via the D2Σ+ v = 1 intermediate state. All members of the six core-penetrating Rydberg series in the n* = 17–20 region and several components of the 17f and 17g core-nonpenetrating Rydberg states have been assigned. While the assignment of core-penetrating Rydberg states is straightforward without use of an effective Hamiltonian model, "spectrum-only" assignment of core-nonpenetrating states is complicated because strong l-uncoupling causes the core-nonpenetrating states to evolve rapidly from Hund's case (b) to Hund's case (d) coupling. We describe "spectrum-only" assignment procedures, developed in the spirit of Gerhard Herzberg, that can be used to assign optical–optical double-resonance spectra of core-penetrating and core-nonpenetrating Rydberg states using only information contained in the spectrum rather than predictions derived from an effective Hamiltonian model. The ambiguities that arise in the assignment of each class of states are discussed in detail.Key words: CaF, electric quadrupole moment, Rydberg states, laser spectroscopy.

Ionization-detected optical–optical double resonance spectroscopic studies of moderate energy Rydberg states of calcium monofluoride

This paper describes a systematic investigation of quasi-bound Rydberg states of calcium monofluoride (CaF) existing between the molecule's υ+ = 0 and 1 ionization thresholds. Experiments utilized ionization-detected optical–optical double resonance spectroscopy to assign states as belonging to one of the six core-penetrating ([Formula: see text] [Formula: see text] 2) or to a core-nonpenetrating ([Formula: see text] [Formula: see text] 3) Rydberg series. Most states observed had effective principal quantum number, ν, between 12 and 18 and one quantum of vibrational excitation in the CaF+ ion-core, although lower ν, υ [Formula: see text] = 2 states were also identified. Core-nonpenetrating states were observed both directly and through avoided crossings with core-penetrating states. Five of the seven [Formula: see text] components in the f-complexes derived from Ca+, 13f and n = 14f, have been identified. We present a detailed analysis of the CaF electronic structure for 12.5 [Formula: see text] ν [Formula: see text] 14.6, υ = 1 using an effective Hamiltonian model to describe CaF+ ion-core-induced [Formula: see text]-mixing between [Formula: see text] [Formula: see text] 3 (s,p, d, and f) Ca+ atomic orbitals. An observed avoided crossing between the 14.19 2Σ+, υ = 1 and 14f ([Formula: see text] = –3), υ = 1 states implies that the previously identified 0.19 Σ+ core-penetrating series has 20–30% f 2υ+-character. The effective Hamiltonian approach accounts for much of the data, however, a complete accounting requires the use of multichannel quantum defect theory (MQDT). An MQDT analysis of the data presented here is provided in a companion paper by Jungen and Roche in this issue. The effective Hamiltonian model enabled derivation of electrostatic properties of the CaF+ core as well as the 0.14Δ series quantum defect derivative, [dδ/dR]Re+, which governs the exchange of energy between the Rydberg electron and the CaF+ ion-core. The CaF+ electric quadrupole moment, defined with the coordinate origin at the center-of-charge, is 11.3 ± 0.5 a.u. PACS Nos.: 33.40+f, 33.80Eh, 33.15Ry, 33.15Ta