Compared with atoms, molecules have a rich internal structure that offers many opportunities for technological and scientific advancement. The study of this structure could yield critical insights into quantum chemistry, new methods for manipulating quantum information, and improved tests of discrete symmetry violation and fundamental constant variation. Harnessing this potential typically requires the preparation of cold molecules in their quantum rovibrational ground state. However, the molecular internal structure severely complicates efforts to produce such samples. Removal of energy stored in long-lived vibrational levels is particularly problematic because optical transitions between vibrational levels are not governed by strict selection rules, which makes laser cooling difficult. Additionally, traditional collisional, or sympathetic, cooling methods are inefficient at quenching molecular vibrational motion. Here we experimentally demonstrate that the vibrational motion of trapped BaCl(+) molecules is quenched by collisions with ultracold calcium atoms at a rate comparable to the classical scattering, or Langevin, rate. This is over four orders of magnitude more efficient than traditional sympathetic cooling schemes. The high cooling rate, a consequence of a strong interaction potential (due to the high polarizability of calcium), along with the low collision energies involved, leads to molecular samples with a vibrational ground-state occupancy of at least 90 per cent. Our demonstration uses a novel thermometry technique that relies on relative photodissociation yields. Although the decrease in vibrational temperature is modest, with straightforward improvements it should be possible to produce molecular samples with a vibrational ground-state occupancy greater than 99 per cent in less than 100 milliseconds. Because sympathetic cooling of molecular rotational motion is much more efficient than vibrational cooling in traditional systems, we expect that the method also allows efficient cooling of the rotational motion of the molecules. Moreover, the technique should work for many different combinations of ultracold atoms and molecules.

Ultracold 174Yb+ ions and 40Ca atoms are confined in a hybrid trap. The charge exchange chemical reaction rate constant between these two species is measured and found to be 4 orders of magnitude larger than recent measurements in other heteronuclear systems. The structure of the CaYb+ molecule is determined and used in a calculation that explains the fast chemical reaction as a consequence of strong radiative charge transfer. A possible explanation is offered for the apparent contradiction between typical theoretical predictions and measurements of the radiative association process in this and other recent experiments.

We demonstrate the integration of a linear quadrupole trap with a simple time-of-flight mass spectrometer with medium-mass resolution (m/Δm ∼ 50) geared towards the demands of atomic, molecular, and chemical physics experiments. By utilizing a novel radial ion extraction scheme from the linear quadrupole trap into the mass analyzer, a device with large trap capacity and high optical access is realized without sacrificing mass resolution. This provides the ability to address trapped ions with laser light and facilitates interactions with neutral background gases prior to analyzing the trapped ions. Here, we describe the construction and implementation of the device as well as present representative ToF spectra. We conclude by demonstrating the flexibility of the device with proof-of-principle experiments that include the observation of molecular-ion photodissociation and the measurement of trapped-ion chemical reaction rates.

The formation of (40)Ca(2)(+) molecular ions is observed in a hybrid (40)Ca magneto-optical and ion trap system. The molecular ion formation process is determined to be photo-associative ionization of ultracold (40)Ca atoms. A lower bound for the two-body rate constant is found to be beta ≥ 2 ± 1 × 10(-15) cm(3) Hz. Ab initio molecular potential curves are calculated for the neutral Ca(2) and ionic Ca(2)(+) molecules and used in a model that identifies the photo-associative ionization pathway. As this technique does not require a separate photo-association laser, it could find use as a simple, robust method for producing ultracold molecular ions.

We demonstrate a simple technique for molecular ion spectroscopy. BaCl + molecular ions are trapped in a linear Paul trap in the presence of a room-temperature He buffer gas and photodissociated by driving an electronic transition from the ground X 1 Σ + state to the repulsive wall of the A 1 Π state. The photodissociation spectrum is recorded by monitoring the induced trap loss of BaCl + ions as a function of excitation wavelength. Accurate molecular potentials and spectroscopic constants are determined. Comparison of the theoretical photodissociation cross-sections with the measurement shows excellent agreement. This study represents the first spectroscopic data for BaCl + and an important step towards the production of ultracold ground-state molecular ions. [5]. In pursuit of these goals, several groups have recently initiated work [6-9] to realize samples of cold, absolute ground-state molecular ions. In fact, Refs. [7][8][9] have already reported the demonstration of species-specific cooling methods to produce molecular ions in the lowest few rotational states.While these molecular ion cooling efforts, which include ultracold atom sympathetic cooling [6], rovibrational optical pumping [7,8], and state-selective ionization [9], are diverse in approach, they share the common need for detailed spectroscopic understanding of diatomic ions. However, compared to that of neutral molecules, spectroscopic data for molecular ions is scarce. This can be attributed to the typically short lifetimes of molecular ions due to fast ion-molecule reactions [10]. A systematic review of the available spectroscopic data for simple diatomic ions was carried out by Berkowitz and Groeneveld [11] in 1983. In recent years, interest has shifted towards large molecular ions, atomic and molecular clusters, and multiply charged ions [12]. Thus, for ultracold molecular ion research to realize its full potential, a new effort in small molecular ion spectroscopy is required.Here, we report the use of a simple and general technique to record the first spectroscopic data for BaCl + -the molecular ion we have proposed to cool in Ref. As an ionically-bonded molecule composed of two closedshell atomic ions, Ba 2+ and Cl − , BaCl + exhibits reduced chemical reactivity compared to other ions and is energetically forbidden from undergoing 2-body chemical reactions with the ultracold calcium atoms used for sympathetic cooling [6]. Further, its large dipole moment and convenient rotational splitting are promising for cavity QED experiments [4]. Thus, these results are important not only as the demonstration of a technique for recording molecular ion spectroscopy, but also as an important first step towards the use and application of a generic, robust method for the production of cold ground-state molecular ions.Spectroscopic data is taken using a trap-depletion approach. BaCl + ions are trapped in a linear Paul trap in the presence of a room-temperature He buffer gas and photodissociated by driving an electronic transition from the ground X 1 Σ + st...