arXiv subjects

John M. Doyle

Publications and source records attributed to John M. Doyle.

At least 91 records · Page 5Linked to original sources

arXiv2013

Advanced Cold Molecule Electron EDM

Measurement of a non-zero electric dipole moment (EDM) of the electron within a few orders of magnitude of the current best limit of |d_e| < 1.05 e -27 e cm would be an indication of physics beyond the Standard Model. The ACME Collaboration is searching for an electron EDM by performing a precision measurement of electron spin precession in the metastable H state of thorium monoxide (ThO) using a slow, cryogenic beam. We discuss the current status of the experiment. Based on a data set acquired from 14 hours of running time over a period of 2 days, we have achieved a 1-sigma statistical uncertainty of 1 e -28 e cm/T^(1/2), where T is the running time in days.

physics.atom-ph↗

arXiv2013

Sensitive Chiral Analysis via Microwave Three-wave Mixing

We demonstrate chirality-induced three-wave mixing in the microwave regime, using rotational transitions in cold gas-phase samples of 1,2-propanediol and 1,3-butanediol. We show that bulk three-wave mixing, which can only be realized in a chiral environment, provides a sensitive, species selective probe of enantiomeric excess and is applicable to a broad class of molecules. The doubly resonant condition provides simultaneous identification of species and of handedness, which should allow sensitive chiral analysis even within a complex mixture.

physics.chem-ph↗

arXiv2012

Spin Dependent Collision of Ultracold Metastable Atoms

Spin-polarized metastable atoms of ultracold ytterbium are trapped at high density and their inelastic collisional properties are measured. We reveal that in collisions of Yb(3P2) with Yb(1S0) there is relatively weak inelastic loss, but with a significant spin-dependence consistent with Zeeman sublevel changes as being the dominant decay process. This is in strong contrast to our observations of Yb(3P2)-Yb(3P2) collisional loss, which are, at low field, much more rapid and have essentially no spin dependence. Our results give a guideline to use the 3P2 states in many possible applications.

physics.atom-ph↗

arXiv2011

The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

Beams of atoms and molecules are stalwart tools for spectroscopy and studies of collisional processes. The supersonic expansion technique can create cold beams of many species of atoms and molecules. However, the resulting beam is typically moving at a speed of 300-600 m/s in the lab frame, and for a large class of species has insufficient flux (i.e. brightness) for important applications. In contrast, buffer gas beams can be a superior method in many cases, producing cold and relatively slow molecules in the lab frame with high brightness and great versatility. There are basic differences between supersonic and buffer gas cooled beams regarding particular technological advantages and constraints. At present, it is clear that not all of the possible variations on the buffer gas method have been studied. In this review, we will present a survey of the current state of the art in buffer gas beams, and explore some of the possible future directions that these new methods might take.

physics.atom-ph↗

arXiv2011

Magnetic and electric dipole moments of the $H\ {}^3Δ_1$ state in ThO

The metastable $H \ {}^3Δ_1$ state in the thorium monoxide (ThO) molecule is highly sensitive to the presence of a CP-violating permanent electric dipole moment of the electron (eEDM). The magnetic dipole moment $μ_H$ and the molecule-fixed electric dipole moment $D_H$ of this state are measured in preparation for a search for the eEDM. The small magnetic moment $μ_H = 8.5(5) \times 10^{-3} \ μ_B$ displays the predicted cancellation of spin and orbital contributions in a ${}^3 Δ_1$ paramagnetic molecular state, providing a significant advantage for the suppression of magnetic field noise and related systematic effects in the eEDM search. In addition, the induced electric dipole moment is shown to be fully saturated in very modest electric fields ($<$ 10 V/cm). This feature is favorable for the suppression of many other potential systematic errors in the ThO eEDM search experiment.

physics.atom-ph↗

arXiv2011

Quantum degenerate mixtures of alkali and alkaline-earth-like atoms

We realize simultaneous quantum degeneracy in mixtures consisting of the alkali and alkalineearth-like atoms Li and Yb. This is accomplished within an optical trap by sympathetic cooling of the fermionic isotope 6Li with evaporatively cooled bosonic 174Yb and, separately, fermionic 173Yb.Using cross-thermalization studies, we also measure the elastic s-wave scattering lengths of both Li-Yb combinations, |a6Li-174Yb| = 1.0\pm0.2 nm and |a6Li-173Yb| = 0.9\pm0.2 nm. The equality of these lengths is found to be consistent with mass-scaling analysis. The quantum degenerate mixtures of Li and Yb, as realized here, can be the basis for creation of ultracold molecules with electron spin degrees of freedom, studies of novel Efimov trimers, and impurity probes of superfluid systems.

physics.atom-ph↗

arXiv2011

Formation and dynamics of van der Waals molecules in buffer-gas traps

We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps.

physics.atm-clus↗

arXiv2011

Cold and Slow Molecular Beam

Employing a two-stage cryogenic buffer gas cell, we produce a cold, hydrodynamically extracted beam of calcium monohydride molecules with a near effusive velocity distribution. Beam dynamics, thermalization and slowing are studied using laser spectroscopy. The key to this hybrid, effusive-like beam source is a "slowing cell" placed immediately after a hydrodynamic, cryogenic source [Patterson et al., J. Chem. Phys., 2007, 126, 154307]. The resulting CaH beams are created in two regimes. One modestly boosted beam has a forward velocity of vf = 65 m/s, a narrow velocity spread, and a flux of 10^9 molecules per pulse. The other has the slowest forward velocity of vf = 40 m/s, a longitudinal temperature of 3.6 K, and a flux of 5x10^8 molecules per pulse.

physics.atom-ph↗

arXiv2011

A cryogenic beam of refractory, chemically reactive molecules with expansion cooling

Cryogenically cooled buffer gas beam sources of the molecule thorium monoxide (ThO) are optimized and characterized. Both helium and neon buffer gas sources are shown to produce ThO beams with high flux, low divergence, low forward velocity, and cold internal temperature for a variety of stagnation densities and nozzle diameters. The beam operates with a buffer gas stagnation density of ~10^15-10^16 cm^-3 (Reynolds number ~1-100), resulting in expansion cooling of the internal temperature of the ThO to as low as 2 K. For the neon (helium) based source, this represents cooling by a factor of about 10 (2) from the initial nozzle temperature of about 20 K (4 K). These sources deliver ~10^11 ThO molecules in a single quantum state within a 1-3 ms long pulse at 10 Hz repetition rate. Under conditions optimized for a future precision spectroscopy application [A C Vutha et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 074007], the neon-based beam has the following characteristics: forward velocity of 170 m/s, internal temperature of 3.4 K, and brightness of 3x10^11 ground state molecules per steradian per pulse. Compared to typical supersonic sources, the relatively low stagnation density of this source, and the fact that the cooling mechanism relies only on collisions with an inert buffer gas, make it widely applicable to many atomic and molecular species, including those which are chemically reactive, such as ThO.

physics.atom-ph↗

arXiv2010

Search for the electric dipole moment of the electron with thorium monoxide

The electric dipole moment of the electron (eEDM) is a signature of CP-violating physics beyond the Standard Model. We describe an ongoing experiment to measure or set improved limits to the eEDM, using a cold beam of thorium monoxide (ThO) molecules. The metastable $H {}^3Δ_1$ state in ThO has important advantages for such an experiment. We argue that the statistical uncertainty of an eEDM measurement could be improved by as much as 3 orders of magnitude compared to the current experimental limit, in a first-generation apparatus using a cold ThO beam. We describe our measurements of the $H$ state lifetime and the production of ThO molecules in a beam, which provide crucial data for the eEDM sensitivity estimate. ThO also has ideal properties for the rejection of a number of known systematic errors; these properties and their implications are described.

physics.atom-ph↗

arXiv2010

Cold N+NH Collisions in a Magnetic Trap

We present an experimental and theoretical study of atom-molecule collisions in a mixture of cold, trapped atomic nitrogen and NH molecules at a temperature of $\sim 600$~mK. We measure a small N+NH trap loss rate coefficient of $k^{(\mathrm{N+NH})}_\mathrm{loss} = 8(4) \times 10^{-13}$~cm$^{3}$s$^{-1}$. Accurate quantum scattering calculations based on {\it ab initio} interaction potentials are in agreement with experiment and indicate the magnetic dipole interaction to be the dominant loss mechanism. Our theory further indicates the ratio of N+NH elastic to inelastic collisions remains large ($>100$) into the mK regime.

physics.atom-ph↗

arXiv2010

Cold heteromolecular dipolar collisions

We present the first experimental observation of cold collisions between two different species of neutral polar molecules, each prepared in a single internal quantum state. Combining for the first time the techniques of Stark deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the enhancement of molecular interaction time by 10$^5$. This has enabled an absolute measurement of the total trap loss cross sections between OH and ND$_3$ at a mean collision energy of 3.6 cm$^{-1}$ (5 K). Due to the dipolar interaction, the total cross section increases upon application of an external polarizing electric field. Cross sections computed from \emph{ab initio} potential energy surfaces are in excellent agreement with the measured value at zero external electric field. The theory presented here represents the first such analysis of collisions between a $^2Π$ radical and a closed-shell polyatomic molecule.

physics.chem-ph↗

arXiv2010

Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He

We have measured the ratio of the diffusion cross-section to the angular momentum reorientation cross-section in the colliding Fe-3He and Ni-3He systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer gas. Elastic collisions rapidly cool the translational temperature of the ablated atoms to the helium temperature. The cross-section ratio is extracted by measuring the decays of the atomic Zeeman sublevels. For our experimental conditions, thermal energy is comparable to the Zeeman splitting. As a result, thermal excitations between Zeeman sublevels significantly impact the observed decay. To determine the cross-section ratio accurately, we introduce a model of Zeeman state dynamics that includes thermal excitations. We find the cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a 0.8 T magnetic field. These measurements are interpreted in the context of submerged shell suppression of spin relaxation as studied previously in transition metals and rare earth atoms.

physics.atom-ph↗

arXiv2009

Permeability of Noble Gases through Kapton, Butyl, Nylon, and "Silver Shield"

Noble gas permeabilities and diffusivities of Kapton, butyl, nylon, and "Silver Shield" are measured at temperatures between 22C and 115C. The breakthrough times and solubilities at 22C are also determined. The relationship of the room temperature permeabilities to the noble gas atomic radii is used to estimate radon permeability for each material studied. For the noble gases tested, Kapton and Silver Shield have the lowest permeabilities and diffusivities, followed by nylon and butyl, respectively.

physics.ins-det↗

arXiv2009

Large spin relaxation rates in trapped submerged-shell atoms

Spin relaxation due to atom-atom collisions is measured for magnetically trapped erbium and thulium atoms at a temperature near 500 mK. The rate constants for Er-Er and Tm-Tm collisions are 3.0 times 10^-10 cm^3 s^-1 and 1.1 times 10^-10 cm^3 s^-1, respectively, 2-3 orders of magnitude larger than those observed for highly magnetic S-state atoms. This is strong evidence for an additional, dominant, spin relaxation mechanism, electrostatic anisotropy, in collisions between these "submerged-shell" L > 0 atoms. These large spin relaxation rates imply that evaporative cooling of these atoms in a magnetic trap will be highly inefficient.

physics.atom-ph↗

arXiv2009

Realization of Coherent Optically Dense Media via Buffer-Gas Cooling

We demonstrate that buffer-gas cooling combined with laser ablation can be used to create coherent optical media with high optical depth and low Doppler broadening that offers metastable states with low collisional and motional decoherence. Demonstration of this generic technique opens pathways to coherent optics with a large variety of atoms and molecules. We use helium buffer gas to cool 87Rb atoms to below 7 K and slow atom diffusion to the walls. Electromagnetically induced transparency (EIT) in this medium allows for 50% transmission in a medium with initial OD >70 and for slow pulse propagation with large delay-bandwidth products. In the high-OD regime, we observe high-contrast spectrum oscillations due to efficient four-wave mixing.

quant-ph↗

arXiv2008

Intense Atomic and Molecular Beams via Neon Buffer Gas Cooling

We realize a continuous guided beam of cold deuterated ammonia with a flux of 3e11 ND3 molecules/s and a continuous free-space beam of cold potassium with a flux of 1e16 K atoms/s. A novel feature of the buffer gas source used to produce these beams is cold neon, which, due to intermediate Knudsen number beam dynamics, produces a forward velocity and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and molecular species with significant vapor pressure below 1000 K. This source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or molecular gases.

physics.atom-ph↗

arXiv2008

Mechanism of Collisional Spin Relaxation in Triplet-Sigma Molecules

We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold Triplet-Sigma molecules with helium atoms in a magnetic field. All four stable isotopomers of the imidogen (NH) molecule are magnetically trapped and studied in collisions with 3He and 4He. The 4He data support the predicted inverse square dependence of the collision induced Zeeman relaxation rate coefficient on the molecular rotational constant B. The measured 3He rate coefficients are much larger than 4He and depend less strongly on B, and the theoretical analysis indicates they are strongly affected by a shape resonance. The results demonstrate the influence of molecular structure on collisional energy transfer at low temperatures.

physics.atom-ph↗