Publications
114 results found
Jarvis KN, Devlin JA, Wall TE, et al., 2018, Blue-detuned magneto-optical trap, Physical Review Letters, Vol: 120, ISSN: 0031-9007
We present the properties and advantages of a new magneto-optical trap (MOT) where blue- detuned light drives ‘type-II’ transitions that have dark ground states. Using ⁸⁷Rb, we reach a radiation-pressure-limited density exceeding 10¹¹ cm⁻³ and a temperature below 30 μK. The phase-space density is higher than in normal atomic MOTs, and a million times higher than comparable red-detuned type-II MOTs, making the blue-detuned MOT particularly attractive for molecular MOTs which rely on type-II transitions. The loss of atoms from the trap is dominated by ultracold collisions between Rb atoms. For typical trapping conditions, we measure a loss rate of 1.8(4) × 10⁻¹⁰ cm³ s⁻¹.
Truppe S, Williams HJ, Hambach M, et al., 2017, Molecules cooled below the Doppler limit, Nature Physics, Vol: 13, Pages: 1173-1176, ISSN: 1745-2473
The ability to cool atoms below the Doppler limit -- the minimum temperaturereachable by Doppler cooling -- has been essential to most experiments withquantum degenerate gases, optical lattices and atomic fountains, among manyother applications. A broad set of new applications await ultracold molecules,and the extension of laser cooling to molecules has begun. A molecularmagneto-optical trap has been demonstrated, where molecules approached theDoppler limit. However, the sub-Doppler temperatures required for mostapplications have not yet been reached. Here we cool molecules to 50 uK, wellbelow the Doppler limit, using a three-dimensional optical molasses. Theseultracold molecules could be loaded into optical tweezers to trap arbitraryarrays for quantum simulation, launched into a molecular fountain for testingfundamental physics, and used to study ultracold collisions and ultracoldchemistry.
Williams H, Truppe S, Hambach M, et al., 2017, Characteristics of a magneto-optical trap of molecules, New Journal of Physics, Vol: 19, ISSN: 1367-2630
We present the properties of a magneto-optical trap (MOT) of CaFmolecules. We study the process of loading the MOT from a decelerated bu er-gas-cooled beam, and how best to slow this molecular beam in order to capture the most molecules. We determine how the number of molecules, the photon scattering rate, the oscillation frequency, damping constant, temperature, cloud size and lifetime depend on the key parameters of the MOT, especially the intensity and detuning of the main cooling laser. We compare our results to analytical and numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF molecules. We load up to 2 x 10⁴ molecules, and measure a maximum scattering rate of 2.5 x 10⁶ s⁻¹ per molecule, a maximum oscillation frequency of 100 Hz, a maximum damping constant of 500 s⁻¹, and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 μK is obtained by ramping down the laser intensity to low values. The lifetime, typically about 100 ms, is consistent with a leak out of the cooling cycle with a branching ratio of about 6 x 10⁻⁶. The MOT has a capture velocity of about 11 m/s.
Truppe S, Hambach M, Skoff S, et al., 2017, A buffer gas beam source for short, intense and slow molecular pulses, Journal of Modern Optics, Vol: 65, Pages: 246-254, ISSN: 0950-0340
Experiments with cold molecules usually begin with a molecular source. We describe the construction and characteristics of a cryogenic buff er gas source of CaF molecules. The source emits pulses with a typical duration of 240 μs, a mean speed of about 150 m/s, and a flux of 5x 10¹⁰ molecules per steradian per pulse in a single rotational state.
LIM J, Almond J, Tarbutt MR, et al., 2017, The [557]-X²∑⁺ and [561]- X²∑⁺ bands of ytterbium fluoride,¹⁷⁴YbF, Journal of Molecular Spectroscopy, Vol: 338, Pages: 81-90, ISSN: 1096-083X
The [557] - X2Σ+(v = 0, 1, 2, 3) and the [561] - X2Σ+ (v = 2) visible electronic transitions of YbF have been recorded at a near-natural linewidth spectral resolution using both supersonically cooled and buffer-gas cooled beams. The 174YbF isotopologue spectral features were analyzed to produce a new set of spectroscopic parameters for the X2Σ+(v = 2), X2Σ+(v = 3), [557], and [561] states. This study will facilitate ongoing work to produce ultracold YbF molecules by laser cooling in order to improve measurements of the electron’s electric dipole moment.
Tokunaga SK, Hendricks RJ, Tarbutt MR, et al., 2017, High-resolution mid-infrared spectroscopy of buffer-gas-cooled methyltrioxorhenium molecules, New Journal of Physics, Vol: 19, ISSN: 1367-2630
We demonstrate cryogenic buffer-gas cooling of gas-phase methyltrioxorhenium (MTO). This molecule is closely related to chiral organometallic molecules where the parity-violating energy differences between enantiomers is measurable. The molecules are produced with a rotational temperature of approximately 6 K by laser ablation of an MTO pellet inside a cryogenic helium buffer gas cell. Facilitated by the low temperature, we demonstrate absorption spectroscopy of the 10.2 μm antisymmetric Re=O stretching mode of MTO with a resolution of 8 MHz and a frequency accuracy of 30 MHz. We partially resolve the hyperfine structure and measure the nuclear quadrupole coupling of the excited vibrational state. Our ability to produce dense samples of complex molecules of this type at low temperatures represents a key step towards a precision measurement of parity violation in a chiral species.
Truppe S, Williams HJ, Fitch NJ, et al., 2017, An intense, cold, velocity-controlled molecular beam by frequency-chirped laser slowing, NEW JOURNAL OF PHYSICS, Vol: 19, ISSN: 1367-2630
Using frequency-chirped radiation pressure slowing, we precisely control the velocity of a pulsed CaF molecular beam down to a few m s–1, compressing its velocity spread by a factor of 10 while retaining high intensity: at a velocity of 15 m s–1 the flux, measured 1.3 m from the source, is 7 × 105 molecules per cm2 per shot in a single rovibrational state. The beam is suitable for loading a magneto-optical trap or, when combined with transverse laser cooling, improving the precision of spectroscopic measurements that test fundamental physics. We compare the frequency-chirped slowing method with the more commonly used frequency-broadened slowing method.
Asselin P, Berger Y, Huet TR, et al., 2017, Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 19, Pages: 4576-4587, ISSN: 1463-9076
Precise spectroscopic analysis of polyatomic molecules enables many striking advances in physical chemistry and fundamental physics. We use several new high-resolution spectroscopic devices to improve our understanding of the rotational and rovibrational structure of methyltrioxorhenium (MTO), the achiral parent of a family of large oxorhenium compounds that are ideal candidate species for a planned measurement of parity violation in chiral molecules. Using millimetre-wave and infrared spectroscopy in a pulsed supersonic jet, a cryogenic buffer gas cell, and room temperature absorption cells, we probe the ground state and the Re[double bond, length as m-dash]O antisymmetric and symmetric stretching excited states of both CH3187ReO3 and CH3185ReO3 isotopologues in the gas phase with unprecedented precision. By extending the rotational spectra to the 150–300 GHz range, we characterize the ground state rotational and hyperfine structure up to J = 43 and K = 41, resulting in refinements to the rotational, quartic and hyperfine parameters, and the determination of sextic parameters and a centrifugal distortion correction to the quadrupolar hyperfine constant. We obtain rovibrational data for temperatures between 6 and 300 K in the 970–1015 cm−1 range, at resolutions down to 8 MHz and accuracies of 30 MHz. We use these data to determine more precise excited-state rotational, Coriolis and quartic parameters, as well as the ground-state centrifugal distortion parameter DK of the 187Re isotopologue. We also account for hyperfine structure in the rovibrational transitions and hence determine the upper state rhenium atom quadrupole coupling constant eQq′.
Devlin J, Tarbutt M, 2016, Three-dimensional Doppler, polarization-gradient, and magneto-optical forces for atoms and molecules with dark states, New Journal of Physics, Vol: 18, ISSN: 1367-2630
We theoretically investigate the damping and trapping forces in a three-dimensional magneto-optical trap (MOT), by numerically solving the optical Bloch equations. We focus on the case where there are dark states because the atom is driven on a ”type-II" system where the angular momentum of the excited state, F', is less than or equal to that of the ground state, F. For these systems we find that the force in a three-dimensional light field has very different behaviour to its one-dimensional counterpart. This differs from the more commonly used “type-I" systems (F' = F +1) where the 1D and 3D behaviours are similar. Unlike type-I systems where, for red-detuned light, both Doppler and sub-Doppler forces damp the atomic motion towards zero velocity, in type-II systems in 3D, the Doppler force and polarization gradient force have opposite signs. As a result, the atom is driven towards a non-zero equilibrium velocity, v₀, where the two forces cancel. We find that v₀² scales linearly with the intensity of the light and is fairly insensitive to the detuning from resonance. We also discover a new magneto-optical force that alters the normal MOT force at low magnetic fields and whose influence is greatest in the type-II systems. We discuss the implications of these findings for the laser cooling and magneto-optical trapping of molecules where type-II transitions are unavoidable in realising closed optical cycling transitions.
Fitch N, Tarbutt M, 2016, Principles and design of a Zeeman-Sisyphus decelerator for molecular beams, Chemphyschem, Vol: 17, Pages: 3609-3623, ISSN: 1439-7641
We explore a technique for decelerating molecules using a static magnetic eld and optical pumping. Molecules travel through a spatially varying magnetic fi eld and are repeatedly pumped into a weak-field seeking state as they move towards each strong field region, and into a strong-fi eld seeking state as they move towards weak fi eld. The method is time-independentand so is suitable for decelerating both pulsed and continuous molecular beams. By using guiding magnets at each weak field region, the beamcan be simultaneously guided and decelerated. By tapering the magnetic field strength in the strong field regions, and exploiting the Doppler shift, the velocity distribution can be compressed during deceleration. We develop the principles of this deceleration technique, provide a realistic design, use numerical simulations to evaluate its performance for a beam of CaF, and compare this performance to other deceleration methods.
Fitch NJ, Tarbutt MR, 2016, Principles and design of a Zeeman-Sisyphus decelerator for molecular beams, ChemPhysChem, Vol: 17, Pages: 3609-3623, ISSN: 1439-4235
We explore a technique for decelerating molecules using a static magnetic field and optical pumping. Molecules travel through a spatially varying magnetic field and are repeatedly pumped into a weak-field seeking state as they move towards each strong field region, and into a strong-field seeking state as they move towards weak field. The method is time-independent and so is suitable for decelerating both pulsed and continuous molecular beams. By using guiding magnets at each weak field region, the beam can be simultaneously guided and decelerated. By tapering the magnetic field strength in the strong field regions, and exploiting the Doppler shift, the velocity distribution can be compressed during deceleration. We develop the principles of this deceleration technique, provide a realistic design, use numerical simulations to evaluate its performance for a beam of CaF, and compare this performance to other deceleration methods.
Guttridge A, Hopkins SA, Kemp SL, et al., 2016, Direct loading of a large Yb MOT on the S-1(0) -> P-3(1) transition, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 49, ISSN: 0953-4075
Hopkins SA, Butler K, Guttridge A, et al., 2016, A versatile dual-species Zeeman slower for caesium and ytterbium (vol 87, 043109, 2016), Review of Scientific Instruments, Vol: 87, ISSN: 1089-7623
Hopkins SA, Butler K, Guttridge A, et al., 2016, A versatile dual-species Zeeman slower for caesium and ytterbium, Review of Scientific Instruments, Vol: 87, ISSN: 1089-7623
We describe the design, construction, and operation of a versatile dual-species Zeeman slower for both Cs and Yb, which is easily adaptable for use with other alkali metals and alkaline earths. With the aid of analytic models and numerical simulation of decelerator action, we highlight several real-world problems affecting the performance of a slower and discuss effective solutions. To capture Yb into a magneto-optical trap(MOT), we use the broad ¹S0 to ¹P1 transition at 399 nm for the slower and the narrow ¹S0 to ³P1 intercombination line at 556 nm for the MOT. The Cs MOT and slower both use the D2 line (6²S1/2 to 6²P3/2 at 852 nm. The slower can be switched between loading Yb or Cs in under 0.1 s. We demonstrate that within a few seconds the Zeeman slower loads more than 10⁹ Yb atoms and 10⁸ Cs atoms into their respective MOTs. These are ideal starting numbers for further experiments on ultracold mixtures and molecules.
Kemp SL, Butler KL, Freytag R, et al., 2016, Production and characterization of a dual species magneto-optical trap of cesium and ytterbium, Review of Scientific Instruments, Vol: 87, ISSN: 1089-7623
We describe an apparatus designed to trap and cool a Yb and Cs mixture. The apparatus consists of a dual species effusive oven source, dual species Zeeman slower, magneto-optical traps in a single ultra-high vacuum science chamber, and the associated laser systems. The dual species Zeeman slower is used to load sequentially the two species into their respective traps. Its design is flexible and may be adapted for other experiments with different mixtures of atomic species. The apparatus provides excellent optical access and can apply large magnetic bias fields to the trapped atoms. The apparatus regularly produces 108 Cs atoms at 13.3 μK in an optical molasses, and 109174Y b atoms cooled to 22 μK in a narrowband magneto-optical trap.
Norrgard EB, McCarron DJ, Steinecker MH, et al., 2016, Submillikelvin dipolar molecules in a radio-frequency magneto-optical trap, Physical Review Letters, Vol: 116, ISSN: 1079-7114
We demonstrate a scheme for magneto-optically trapping strontium monofluoride (SrF) molecules at temperatures one order of magnitude lower and phase space densities 3 orders of magnitude higher than obtained previously with laser-cooled molecules. In our trap, optical dark states are destabilized by rapidly and synchronously reversing the trapping laser polarizations and the applied magnetic field gradient. The number of molecules and trap lifetime are also significantly improved from previous work by loading the trap with high laser power and then reducing the power for long-term trapping. With this procedure, temperatures as low as 400 μK are achieved.
Lim J, Frye MD, Hutson JM, et al., 2015, Modeling sympathetic cooling of molecules by ultracold atoms, Physical Review A, Vol: 92, ISSN: 1094-1622
We model sympathetic cooling of ground-state CaF molecules by ultracold Li and Rb atoms. The molecules are moving in a microwave trap, while the atoms are trapped magnetically. We calculate the differential elastic cross sections for CaF-Li and CaF-Rb collisions, using model Lennard-Jones potentials adjusted to give typical values for the s-wave scattering length. Together with trajectory calculations, these differential cross sections are used to simulate the cooling of the molecules, the heating of the atoms, and the loss of atoms from the trap. We show that a hard-sphere collision model based on an energy-dependent momentum transport cross section accurately predicts the molecule cooling rate but underestimates the rates of atom heating and loss. Our simulations suggest that Rb is a more effective coolant than Li for ground-state molecules, and that the cooling dynamics is less sensitive to the exact value of the s-wave scattering length when Rb is used. Using realistic experimental parameters, we find that molecules can be sympathetically cooled to 100μK in about 10 s. By applying evaporative cooling to the atoms, the cooling rate can be increased and the final temperature of the molecules can be reduced to 1 μK within 30 s.
Tarbutt MR, Steimle TC, 2015, Modeling magneto-optical trapping of CaF molecules, Physical Review A, Vol: 92, ISSN: 1094-1622
Magneto-optical trapping forces for molecules are far weaker than for alkali atoms because thephoton scattering rate is reduced when there are multiple ground states, and because of opticalpumping into dark states. The force is further reduced when the upper state has a much smallerZeeman splitting than the lower state. We use a rate model to estimate the strength of the trappingand damping forces in a magneto-optical trap (MOT) of CaF molecules, using either the A2Π1/2- X2Σ+ transition or the B2Σ+ - X2Σ+ transition. We identify a new mechanism of magnetoopticaltrapping that arises when, in each beam of the MOT, two laser components with oppositepolarizations and different detunings address the same transition. This mechanism produces a strongtrapping force even when the upper state has little or no Zeeman splitting. It is the main mechanismresponsible for the trapping force when the A2Π1/2 - X2Σ+ transition is used.
Devlin J, Tarbutt MR, Kokkin DL, et al., 2015, Measurements of the Zeeman effect in the A(2)Pi and B-2 Sigma(+) states of calcium fluoride, Journal of Molecular Spectroscopy, Vol: 317, Pages: 1-9, ISSN: 1096-083X
The magnetic tuning of the low rotational levels in the (v = 0) X2Σ+, (v = 0) A2Π, and (v = 0) B2Σ+ electronic states of calcium monofluoride, CaF, have been experimentally investigated using high resolution optical Zeeman spectroscopy of a cold molecular beam. The observed Zeeman shifts and splittings are successfully modeled using a traditional effective Hamiltonian approach to account for the interaction between the (v = 0) A2Π and (v = 0) B2Σ+ states. The determined magnetic g-factors for the X2Σ+, B2Σ+ and A2Π states are compared to those predicted by perturbation theory.
Dunseith DP, Truppe S, Hendricks RJ, et al., 2015, A high quality, efficiently coupled microwave cavity for trapping cold molecules, Journal of Physics B - Atomic Molecular and Optical Physics, Vol: 48, ISSN: 0953-4075
Tarbutt MR, 2015, Magneto-optical trapping forces for atoms and molecules with complex level structures, NEW JOURNAL OF PHYSICS, Vol: 17, ISSN: 1367-2630
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- Citations: 67
Hendricks RJ, Holland DA, Truppe S, et al., 2014, Vibrational branching ratios and hyperfine structure of 11BH and its suitability for laser cooling, Frontiers in Physics, Vol: 2, ISSN: 2296-424X
The simple structure of the BH molecule makes it an excellent candidate for direct laser cooling. We measure the branching ratios for the decay of the A1Π (v′ = 0) state to vibrational levels of the ground state, X1Σ+, and find that they are exceedingly favorable for laser cooling. We verify that the branching ratio for the spin-forbidden transition to the intermediate a3Π state is inconsequentially small. We measure the frequency of the lowest rotational transition of the X state, and the hyperfine structure in the relevant levels of both the X and A states, and determine the nuclear electric quadrupole and magnetic dipole coupling constants. Our results show that, with a relatively simple laser cooling scheme, a Zeeman slower and magneto-optical trap can be used to cool, slow and trap BH molecules.
Smallman IJ, Wang F, Steimle TC, et al., 2014, Radiative branching ratios for excited states of <SUP>174</SUP>YbF: Application to laser cooling, JOURNAL OF MOLECULAR SPECTROSCOPY, Vol: 300, Pages: 3-6, ISSN: 0022-2852
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- Citations: 28
Truppe S, Hendricks RJ, Tokunaga SK, et al., 2014, Microwave spectroscopy of A-doublet transitions in the ground state of CH, JOURNAL OF MOLECULAR SPECTROSCOPY, Vol: 300, Pages: 70-78, ISSN: 0022-2852
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Zhelyazkova V, Cournol A, Wall TE, et al., 2014, Laser cooling and slowing of CaF molecules, Physical Review A, Vol: 89, ISSN: 1094-1622
We demonstrate slowing and longitudinal cooling of a supersonic beam of CaF molecules using counterpropagating laser light resonant with a closed rotational and almost-closed vibrational transition. A group of molecules are decelerated by about 20 m/s by applying light of a fixed frequency for 1.8 ms. Their velocity spread is reduced, corresponding to a final temperature of about 300 mK. The velocity is further reduced by chirping the frequency of the light to keep it in resonance as the molecules slow down.
Hinds EA, Truppe S, Hendricks RJ, et al., 2014, Microwave spectroscopy of Λ-doublet transitions in the ground state of CH, Journal of Molecular Spectroscopy, ISSN: 0022-2852
Hudson JJ, Tarbutt MR, Sauer BE, et al., 2014, Stochastic multi-channel lock-in detection, NEW JOURNAL OF PHYSICS, Vol: 16, ISSN: 1367-2630
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Truppe S, Hendricks RJ, Hinds EA, et al., 2013, Measurement of the lowest millimeter-wave transition frequency of the CH radical, Astrophysical Journal, Vol: 780, ISSN: 1538-4357
The CH radical offers a sensitive way to test the hypothesis that fundamental constants measured on earth may differ from those observed in other parts of the universe. The starting point for such a comparison is to have accurate laboratory frequencies. Here, we measure the frequency of the lowest millimeter-wave transition of CH, near 535 GHz, with an accuracy of 0.6 kHz. This improves the uncertainty by roughly two orders of magnitude over previous determinations and opens the way for sensitive new tests of varying constants.
Truppe S, Hendricks RJ, Tokunaga SK, et al., 2013, A search for varying fundamental constants using hertz-level frequency measurements of cold CH molecules, Nature Communications, Vol: 4, ISSN: 2041-1723
Many modern theories predict that the fundamental constants depend on time, position or the local density of matter. Here we develop a spectroscopic method for pulsed beams of cold molecules, and use it to measure the frequencies of microwave transitions in CH with accuracy down to 3 Hz. By comparing these frequencies with those measured from sources of CH in the Milky Way, we test the hypothesis that fundamental constants may differ between the high- and low-density environments of the Earth and the interstellar medium. For the fine structure constant we find Δα/α=(0.3±1.1) × 10−7, the strongest limit to date on such a variation of α. For the electron-to-proton mass ratio we find Δμ/μ=(−0.7±2.2) × 10−7. We suggest how dedicated astrophysical measurements can improve these constraints further and can also constrain temporal variation of the constants.
Bulleid NE, Skoff SM, Hendricks RJ, et al., 2013, Characterization of a cryogenic beam source for atoms and molecules, Phys. Chem. Chem. Phys.
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