We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in 229Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the 229Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the short-term stability of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision (short-term stability) of 3×10(-17)<Δf/f<1×10(-15) after 1 s of photon collection may be achieved with a systematic-limited accuracy (long-term stability) of Δf/f∼2×10(-16). Improvement by 10(2)-10(3) of the constraints on the variability of several important fundamental constants also appears possible.

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.

We report the results of a direct search for the 229 Th (I p = 3/2 + ← 5/2 + ) nuclear isomeric transition, performed by exposing 229 Th-doped LiSrAlF6 crystals to tunable vacuum-ultraviolet synchrotron radiation and observing any resulting fluorescence. We also use existing nuclear physics data to establish a range of possible transition strengths for the isomeric transition. We find no evidence for the thorium nuclear transition between 7.3 eV and 8.8 eV with transition lifetime (1-2) s τ (2000-5600) s. This measurement excludes roughly half of the favored transition search area and can be used to direct future searches.

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.

The role of electronic excitation in charge exchange chemical reactions between ultracold Ca atoms and Ba + ions, confined in a hybrid trap, is studied. This prototypical system is energetically precluded from reacting in its ground state, allowing a particularly simple interpretation of the influence of electronic excitation. It is found that while electronic excitation of the ion can critically influence the chemical reaction rate, electronic excitation of the neutral atom is less important. It is also experimentally demonstrated that with the correct choice of the atom-ion pair, it is possible to mitigate the unwanted effects of these chemical reactions in ultracold atom-ion environments, marking an important step towards the next generation of hybrid devices. PACS numbers:Since the inception of laser-cooling, the primary focus of atomic physics has been the development of techniques for the production and study of ultracold matter -an endeavor that, at its core, is centered on gaining full control over matter at the quantum level. This work has been extremely successful, enabling many long-soughtafter goals, such as quantum degenerate gases [1, 2], quantum simulation [3], quantum information [4], and precision measurement of fundamental physics [5,6]. To gain this control, however, most ultracold matter production techniques rely on the scattering of a large number of photons from the system under study, potentially leading to a large degree of electronic excitation. Thus, the atom or molecule being cooled can be in a somewhat peculiar state: its external motion may be characterized by a temperature close to absolute zero, but its internal electronic degree of freedom may be described by a temperature approaching infinity. While this non-thermal distribution of electronic states has some notable important consequences for ultracold atoms [7], most of its effects, such as photochemical reactions [8][9][10], are largely ignored as they occur at rates that have relatively little effect on the system. However, as the field now moves towards producing more complex systems at ultracold temperatures, e.g. molecules [11] and hybrid systems [12,13], the effect of these light-assisted processes must be reevaluated as their rates may be much larger due to, among other things, an increased density of accessible product states and longer range interactions. Thus, there is presently a need to better understand the role of electronic excitation in chemical reactions at ultracold temperatures to enable the next generation of atomic physics experiments.Interestingly, the rapidly emerging field of hybrid atom-ion systems offers a unique opportunity to study ultracold chemical reactions [14][15][16][17]. Like the all-neutral systems of traditional atomic physics, the two trapped species can collide at short-enough range for chemical reactions to proceed; but, unlike all-neutral systems it is possible to maintain a product of the chemical reaction in the trap, since ion trap depths are large relative to the kinetic energy gaine...

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.

We present data that show a cycling transition can be used to detect and image metastable He2 triplet molecules in superfluid helium. We demonstrate that limitations on the cycling efficiency due to the vibrational structure of the molecule can be mitigated by the use of repumping lasers. Images of the molecules obtained using the method are also shown. This technique gives rise to a new kind of ionizing radiation detector. The use of He2 triplet molecules as tracer particles in the superfluid promises to be a powerful tool for visualization of both quantum and classical turbulence in liquid helium.

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