Deceleration and Trapping of SrF Molecules.

We report on the electrostatic trapping of neutral SrF molecules. The molecules are captured from a cryogenic buffer-gas beam source into the moving traps of a 4.5-m-long traveling-wave Stark decelerator. The SrF molecules in X^{2}Σ^{+}(v=0,N=1) state are brought to rest as the velocity of the moving traps is gradually reduced from 190 m/s to zero. The molecules are held for up to 50 ms in multiple electric traps of the decelerator. The trapped packets have a volume (FWHM) of 1 mm^{3} and a velocity spread of 5(1) m/s, which corresponds to a temperature of 60(20) mK. Our result demonstrates a factor 3 increase in the molecular mass that has been Stark decelerated and trapped. Heavy molecules (mass>100 amu) offer a highly increased sensitivity to probe physics beyond the standard model. This work significantly extends the species of neutral molecules of which slow beams can be created for collision studies, precision measurement, and trapping experiments.

Systematic study and uncertainty evaluation of P, T-odd molecular enhancement factors in BaF.

A measurement of the magnitude of the electric dipole moment of the electron (eEDM) larger than that predicted by the Standard Model (SM) of particle physics is expected to have a huge impact on the search for physics beyond the SM. Polar diatomic molecules containing heavy elements experience enhanced sensitivity to parity (P) and time-reversal (T)-violating phenomena, such as the eEDM and the scalar-pseudoscalar (S-PS) interaction between the nucleons and the electrons, and are thus promising candidates for measurements. The NL-eEDM collaboration is preparing an experiment to measure the eEDM and S-PS interaction in a slow beam of cold BaF molecules [P. Aggarwal et al., Eur. Phys. J. D 72, 197 (2018)]. Accurate knowledge of the electronic structure parameters, Wd and Ws, connecting the eEDM and the S-PS interaction to the measurable energy shifts is crucial for the interpretation of these measurements. In this work, we use the finite field relativistic coupled cluster approach to calculate the Wd and Ws parameters in the ground state of the BaF molecule. Special attention was paid to providing a reliable theoretical uncertainty estimate based on investigations of the basis set, electron correlation, relativistic effects, and geometry. Our recommended values of the two parameters, including conservative uncertainty estimates, are 3.13 ±0.12×1024Hzecm for Wd and 8.29 ± 0.12 kHz for Ws.

Dissociation Energy of the Hydrogen Molecule at 10

The ionization energy of ortho-H_{2} has been determined to be E_{I}^{o}(H_{2})/(hc)=124 357.238 062(25) cm^{-1} from measurements of the GK(1,1)-X(0,1) interval by Doppler-free, two-photon spectroscopy using a narrow band 179-nm laser source and the ionization energy of the GK(1,1) state by continuous-wave, near-infrared laser spectroscopy. E_{I}^{o}(H_{2}) was used to derive the dissociation energy of H_{2}, D_{0}^{N=1}(H_{2}), at 35 999.582 894(25) cm^{-1} with a precision that is more than one order of magnitude better than all previous results. The new result challenges calculations of this quantity and represents a benchmark value for future relativistic and QED calculations of molecular energies.

Robust constraint on a drifting proton-to-electron mass ratio at z=0.89 from methanol observation at three radio telescopes.

A limit on a possible cosmological variation of the proton-to-electron mass ratio µ is derived from methanol (CH3OH) absorption lines in the benchmark PKS1830-211 lensing galaxy at redshift z=0.89 observed with the Effelsberg 100-m radio telescope, the Institute de Radio Astronomie Millimétrique 30-m telescope, and the Atacama Large Millimeter/submillimeter Array. Ten different absorption lines of CH3OH covering a wide range of sensitivity coefficients K(µ) are used to derive a purely statistical 1σ constraint of Δµ/µ=(1.5±1.5)×10(-7) for a lookback time of 7.5 billion years. Systematic effects of chemical segregation, excitation temperature, frequency dependence, and time variability of the background source are quantified. A multidimensional linear regression analysis leads to a robust constraint of Δµ/µ=(-1.0±0.8(stat)±1.0(sys))×10(-7).

A supersonic laser ablation beam source with narrow velocity spreads.

A supersonic beam source for SrF and BaF molecules is constructed by combining the expansion of carrier gas (a mixture of 2% SF6 and 98% argon) from an Even-Lavie valve with laser ablation of a barium/strontium metal target at a repetition rate of 10 Hz. Molecular beams with a narrow translational velocity spread are produced at relative values of Δv/v = 0.053(11) and 0.054(9) for SrF and BaF, respectively. The relative velocity spread of the beams produced in our source is lower in comparison with the results from other metal fluoride beams produced in supersonic laser ablation sources. The rotational temperature of BaF is measured to be 3.5 K. The source produces 6 × 108 and 107 molecules per steradian per pulse in the X2Σ+ (ν = 0, N = 1) state of BaF and SrF molecules, respectively, a state amenable to Stark deceleration and laser cooling.

Trapping neutral molecules in a traveling potential well.

A series of pulsed electric fields can be arranged such that it creates a traveling potential well in which neutral dipolar molecules can be confined. This provides a method to transport, to decelerate, and to cool a sample of neutral molecules while maintaining the initial phase-space density. This method is described using the concept of phase stability. The oscillating motion of molecules in the traveling potential well, reaching a minimum velocity spread corresponding to a translational temperature of 4 mK, is experimentally observed.

Molecular reorientation in collisions of OH + Ar.

Orientational effects in rotationally elastic collisions of OH with Ar were studied in a crossed molecular beam setup. A static electric field was applied to orient the molecules before the collision. After the collision the orientation was measured by using a narrow-band laser system to probe the Stark-split states corresponding to different orientations. Differential and integral cross sections for reorientation of the molecular axis have been determined as a function of the initial orientation. The cross section for reorientation by one quantum is 25 A2 with a preference for O-end collisions.

A prototype storage ring for neutral molecules.

The ability to cool and manipulate atoms with light has yielded atom interferometry, precision spectroscopy, Bose-Einstein condensates and atom lasers. The extension of controlled manipulation to molecules is expected to be similarly rewarding, but molecules are not as amenable to manipulation by light owing to a far more complex energy-level spectrum. However, time-varying electric and magnetic fields have been successfully used to control the position and velocity of ions, suggesting that these schemes can also be used to manipulate neutral particles having an electric or magnetic dipole moment. Although the forces exerted on neutral species are many orders of magnitude smaller than those exerted on ions, beams of neutral dipolar molecules have been successfully slowed down in a series of pulsed electric fields and subsequently loaded into an electrostatic trap. Here we extend the scheme to include a prototype electrostatic storage ring made of a hexapole torus with a circumference of 80 cm. After injection, decelerated bunches of deuterated ammonia molecules, each containing about 106 molecules in a single quantum state and with a translational temperature of 10 mK, travel up to six times around the ring. Stochastic cooling might provide a means to increase the phase-space density of the stored molecules in the storage ring, and we expect this to open up new opportunities for molecular spectroscopy and studies of cold molecular collisions.

Slowing heavy, ground-state molecules using an alternating gradient decelerator.

We have decelerated a supersonic beam of 174YbF molecules using a switched sequence of electrostatic field gradients. These molecules are 7 times heavier than any previously decelerated. An alternating gradient structure allows us to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring the molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.