Continuous wave (CW) lasers are the enabling technology for producing ultracold atoms and molecules through laser cooling and trapping. The resulting pristine samples of slow moving particles are the de facto starting point for both fundamental and applied science when a highly-controlled quantum system is required. Laser cooled atoms have recently led to major advances in quantum information, the search to understand dark energy, quantum chemistry, and quantum sensors. However, CW laser technology currently limits laser cooling and trapping to special types of elements that do not include highly abundant and chemically relevant atoms such as hydrogen, carbon, oxygen, and nitrogen. Here, we demonstrate that Doppler cooling and trapping by optical frequency combs may provide a route to trapped, ultracold atoms whose spectra are not amenable to CW lasers. We laser cool a gas of atoms by driving a two-photon transition with an optical frequency comb, an efficient process to which every comb tooth coherently contributes. We extend this technique to create a magneto-optical trap (MOT), an electromagnetic beaker for accumulating the laser-cooled atoms for further study. Our results suggest that the efficient frequency conversion offered by optical frequency combs could provide a key ingredient for producing trapped, ultracold samples of nature's most abundant building blocks, as well as antihydrogen. As such, the techniques demonstrated here may enable advances in fields as disparate as molecular biology and the search for physics beyond the standard model.
We demonstrate the trapping and sympathetic cooling of B$^{+}$ ions in a Coulomb crystal of laser-cooled Ca$^{+}$, We non-destructively confirm the presence of the both B$^+$ isotopes by resonant excitation of the secular motion. The B$^{+}$ ions are loaded by ablation of boron and the secular excitation spectrum also reveals features consistent with ions of the form B$_{n}^{+}$.
The intercombination line of Strontium at 689nm is successfully used in laser cooling to reach the photon recoil limit with Doppler cooling in a magneto-optical traps (MOT). In this paper we present a systematic study of the loading efficiency of such a MOT. Comparing the experimental results to a simple model allows us to discuss the actual limitation of our apparatus. We also study in detail the final MOT regime emphasizing the role of gravity on the position, size and temperature along the vertical and horizontal directions. At large laser detuning, one finds an unusual situation where cool…
We demonstrate the possibility of three-dimensional cooling of neutral atoms by illuminating them with two counterpropagating laser beams of mutually orthogonal linear polarization, where one of the lasers is a speckle field, i.e. a highly disordered but stationary coherent light field. This configuration gives rise to atom cooling in the transverse plane via a Sisyphus cooling mechanism similar to the one known in standard two-dimensional optical lattices formed by several plane laser waves. However, striking differences occur in the spatial diffusion coefficients as well as in local properti…
We report magneto-optical trapping (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). The MOT contains $2.0(5)\times 10^4$ CaOH molecules at a peak density of $3.0(8)\times10^{6}$ cm$^{-3}$. CaOH molecules are further sub-Doppler laser cooled in an optical molasses, to a temperature of 110(4) $μ$K. The temperatures and densities achieved here make CaOH a viable candidate for a wide variety of quantum science applications, including the creation of optical tweezer arrays of CaOH molecules. This work also suggests that laser cooling and magneto-optical trapping of many other polyatomi…
We present the simultaneous cooling and trapping of an isotopic mixture in a magneto-optical trap and we describe the transfer of the mixture into a conservative, far-off resonant dipole trap. The mixture is prepared with a new technique that applies to intermediate and heavy alkaline earth like atoms. In this work, 88Sr and 86Sr are simultaneously loaded first into the magneto-optical trap operated on the 1S0-3P1 spin-forbidden line at 689 nm, and then transferred into the dipole trap. We observe fast inter-species thermalization in the dipole trap which allows one to set a lower bound on the…
Metastability and long-range interactions of Mg, Ca, and Sr in the lowest-energy metastable $^3P_2$ state are investigated. The calculated lifetimes are 38 minutes for Mg*, 118 minutes for Ca*, and 17 minutes for Sr*, supporting feasibility of cooling and trapping experiments. The quadrupole-quadrupole long-range interactions of two metastable atoms are evaluated for various molecular symmetries. Hund's case (c) 4_g potential possesses a large 100-1000 K potential barrier. Therefore magnetic trap losses can possibly be reduced using cold metastable atoms in a stretched M=2 state. Calculations …
Complex molecular structure demands customized solutions to laser cooling by extending its general set of principles and practices. Yttrium monoxide (YO) has unique intramolecular interactions. The Fermi-contact interaction dominates over the spin-rotation coupling, resulting in two manifolds of closely spaced states, with one of them possessing a negligible Landé g-factor. This unique energy level structure favors dual-frequency DC magneto-optical trapping (MOT) and gray molasses cooling (GMC). We report exceptionally robust cooling of YO at 4 $μ$K over a wide range of laser intensity, detuni…
This paper introduces and reviews light forces, atom cooling and atom trapping. The emphasis is on the physics of the basic processes. In discussing conservative forces the semi-classical dressed states are used rather than the usual quantized field dressed states.
Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 μK by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. M…
This review describes the production of atomic strontium samples at ultra-low temperature and at high phase-space density, and their possible use for physical studies and applications. We describe the process of loading a magneto-optical trap from an atomic beam and preparing the sample for high precision measurements. Particular emphasis is given to the applications of ultracold Sr samples, spanning from optical frequency metrology to force sensing at micrometer scale.
We report on a reliable laser system for cooling magnesium atoms in the metastable 3P manifold. The three relevant transitions coupling the 3P to the 3D manifold are near 383 nm and seperated by several hundred GHz. The laser system consists of three diode lasers at 766 nm. All lasers are frequency stabilised to a single pre-stabilised transfer cavity. The applied scheme for frequency control greatly reduces the complexity of operating three lasers combined with resonant frequency doubling stages and provides a high reliability necessary for complex atomic physics experiments.
We discuss a possible one-dimensional trapping and cooling of atoms and molecules due to their non-resonant interaction with the counter-propagating light pulses trains. The counter-propagating pulses form a one-dimensional trap for atoms and molecules, and properly chosen the carrier frequency detuning from the transition frequency of the atoms or molecules keeps the "temperature" of the atomic or molecular ensemble close to the Doppler cooling limit. The calculation by the Monte-Carlo wave function method is carried out for the two-level and three-level schemes of the atom's and the molecule…
We report our experiment on sideband cooling with two Raman transitions in a $Λ$ configuration that allows selective coherent population trapping (CPT) of the motional ground state. The cooling method is applied to $^{87}$Rb atoms in a circularly-polarized one-dimensional optical lattice. Owing to the vector polarizability, the vibration frequency of a trapped atom depends on its Zeeman quantum number, and CPT resonance for a pair of bound states in the $Λ$ configuration depends on their vibrational quantum numbers. We call this scheme motion-selective coherent population trapping (MSCPT) and …
First laser cooling and trapping of the heavy alkaline earth element barium has been achieved based on the strong 6s$^2$ $^1$S$_0$ - 6s6p $^1$P$_1$ transition for the main cooling. Due to the large branching into metastable D-states several additional laser driven transitions are required to provide a closed cooling cycle. A total efficiency of $0.4(1) \cdot 10^{-2}$ for slowing a thermal atomic beam and capturing atoms into a magneto optical trap was obtained. Trapping lifetimes of more than 1.5 s were observed. This lifetime is shortened at high laser intensities by photo ionization losses. …
We investigate cooling mechanisms in magneto-optically and magnetically trapped erbium. We find efficient sub-Doppler cooling in our trap, which can persist even in large magnetic fields due to the near degeneracy of two Lande g factors. Furthermore, a continuously loaded magnetic trap is demonstrated where we observe temperatures below 25 microkelvin. These favorable cooling and trapping properties suggest a number of scientific possibilities for rare-earth atomic physics, including narrow linewidth laser cooling and spectroscopy, unique collision studies, and degenerate bosonic and fermionic…
We propose a scheme that combines velocity-selective coherent population trapping (CPT) and Raman sideband cooling (RSC) for subrecoil cooling of optically trapped atoms outside the Lamb-Dicke regime. This scheme is based on an inverted $\mathsf{Y}$ configuration in an alkali-metal atom. It consists of a $Λ$ formed by two Raman transitions between the ground hyperfine levels and the $D$ transition, allowing RSC along two paths and formation of a CPT dark state. Using state-dependent difference in vibration frequency of the atom in a circularly polarized trap, we can tune the $Λ$ to make only t…
We have successfully loaded a magneto-optic trap for Yb atoms from a thermal source without the use of a Zeeman slower. The source is placed close to the trapping region so that it provides a large flux of atoms that can be cooled and captured. The atoms are cooled on the ${^1S_0} \leftrightarrow {^1P_1}$ transition at 398.8 nm. We have loaded all seven stable isotopes of Yb into the trap. For the most abundant isotope ($^{174}$Yb), we load more than $10^7$ atoms into the trap within 1 s. For the rarest isotope ($^{168}$Yb) with a natural abundance of only 0.13%, we still load about $4 \times …
We present the first extended-cavity diode laser in Littrow configuration operating in the cyan wavelength range around 497 nm. The gallium-nitride based diode laser features a free-space output with up to 60 mW, operates in a single frequency mode, is tunable over a range of more than 8 nm and has a Lorentzian linewidth of less than 90 kHz. A detailed characterization of the tuning capabilities of the diode laser and its emission spectrum is provided. This compact, simple and low cost laser source replaces more complex systems based on frequency doubling and therefore simplifies the developme…
We trap cold, ground-state, argon atoms in a deep optical dipole trap produced by a build-up cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of co-trapped metastable argon atoms using a new type of parametric loss spectroscopy. Using this technique we also determine the polarizability ratio between the ground and the metastable 4s[3/2]$_2$ state to be 40$\…
For laser cooling considerations, we have theoretically investigated the electronic, rovibrational and hypefine structures of BaF molecule. The highly diagonal Franck-Condon factors and the branching ratios for all possible transitions within the lowest-lying four electronic states have also been calculated. Meanwhile, the mixing between metastable A'2Δ and A2Π states and further the lifetime of the Δ state have been estimated since the loss procedure via Δ state would like fatally destroy the main quasi-cycling Σ-Π transition for cooling and trapping. The resultant hyperfine splittings of eac…
Here we report on spectroscopic measurements of the aluminum monofluoride molecule (AlF) that are relevant to laser cooling and trapping experiments. We measure the detailed energy level structure of AlF in the X$^1Σ^+$ electronic ground state, in the A$^1Π$ state, and in the metastable a$^3Π$ state. We determine the rotational, vibrational and electronic branching ratios from the A$^1Π$ state. We also study how the rotational levels split and shift in external electric and magnetic fields. We find that AlF is an excellent candidate for laser cooling on any Q-line of the A$^1Π$ - X$^1Σ^+$ tran…
We report on the production of cold, state-selected H$_2^+$ molecular ions in a linear RF trap. The ions are produced by (3+1) resonance-enhanced multi-photon ionisation (REMPI) of H$_2$, and sympathetically cooled by laser-cooled Be$^+$ ions. After demonstrating and characterizing the REMPI process, we use photodissociation by a deep UV laser at 213~nm to verify the high vibrational purity of the produced H$_2^+$ ion samples. Moreover, the large difference between the photodissociation efficiencies of ions created in the $v=0$ and $v=1$ levels provides a way to detect a $v=0 \to 1$ transition…
Trapping lithium with a big number in a simplified experimental setup has difficulties and challenges today. In this paper, we experimentally demonstrate the enhancement of \textsuperscript{6}Li trapping efficiency in a three-dimensional magneto-optical trap (3D MOT) by using the multiple-sideband cooling in a two-dimensional magneto-optical trap (2D MOT). To improve the number of trapped atoms, we broaden the cooling light spectrum to 102 MHz composed of seven frequency components and then trap atoms with a number of $6.0\times10^8$ which is about 4 times compared to that in the single-freque…
We observe the spontaneous evaporation of atoms confined in a bubble-like rf-dressed trap (Zobay and Garraway, 2001). The atoms are confined in a quadrupole magnetic trap and are dressed by a linearly polarized rf field. The evaporation is related to the presence of holes in the trap, at the positions where the rf coupling vanishes, due to its vectorial character. The final temperature results from a competition between residual heating and evaporation efficiency, which is controlled via the height of the holes with respect to the bottom of the trap. The experimental data are modeled by a Mont…
Laser cooling and trapping are central to modern atomic physics. The workhorse technique in cold-atom physics is the magneto-optical trap (MOT), which combines laser cooling with a restoring force from radiation pressure. For a variety of atomic species, MOTs can capture and cool large numbers of particles to ultracold temperatures (<1 mK); this has enabled the study of a wide range of phenomena from optical clocks to ultracold collisions whilst also serving as the ubiquitous starting point for further cooling into the regime of quantum degeneracy. Magneto-optical trapping of molecules could p…
We show that it is possible to cool interacting pairs of atoms by a lin $\perp$ lin Sisyphus-like laser cooling scheme using counter-propagating photoassociation (PA) lasers. It is shown that the center-of-mass motion (c.m.) of atom pairs can be trapped in molecular spin-dependent periodic potentials generated by the lasers. The proposed scheme is most effective for narrow-line PA transitions. We illustrate this with numerical calculations using fermionic $^{171}$Yb atoms as an example.
A new scheme of three-dimensional (3D) all-optical (nonmagnetic) cooling and trapping of resonant atoms, based on using of so-called rectified radiation forces in non-monochromatic light fields is presented. It can be applied to the atoms with a tripod-type configuration of levels: atoms (ions) with the quantum transition F=1 \to F=0. The scheme proposed provides a long-term trapping of such atoms in deep light-induced potential wells. Moreover, the atom temperature can continuously be changed by varying field parameters in quite a large range (from super-Doppler to sub-Doppler values) without…
We present a realization of a magneto-optical trap of mercury atoms on the intercombination line. We report on trapping of all stable mercury isotopes. We characterize the effect of laser detuning, laser intensity, and gradient field on the trapping performance of our system. The atom number for the most abundant isotope Hg-202 is 50 million atoms. Moreover, we study the difference in cooling processes for bosonic and fermionic isotopes. We observe agreement with the Doppler cooling theory for the bosonic species and show sub-Doppler cooling for the fermionic species. We reach a phase space de…
Laser cooling on weak transitions is a useful technique for reaching ultracold temperatures in atoms with multiple valence electrons. However, for strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT) is destabilized by competition between optical and magnetic forces. We overcome this difficulty in Er by developing an unusual narrow-line MOT that balances optical and magnetic forces using laser light tuned to the blue side of a narrow (8 kHz) transition. The trap population is spin-polarized with temperatures reaching below 2 microkelvin. Our results constitute an alter…
Alkaline earth monoalkoxide free radicals (MORs) have molecular properties conducive to direct laser cooling to sub-millikelvin temperatures. Using dispersed laser induced fluorescence (DLIF) measurements from a pulsed supersonic molecular beam source we determine vibrational branching ratios and Franck-Condon factors for the MORs CaOH and CaOCH$_{3}$. With narrow linewidth continuous-wave dye laser excitation, we precisely measure fluorescence branching for both $\tilde{X}-\tilde{A}$ and $\tilde{X}-\tilde{B}$ electronic systems in each molecule. Weak symmetry-forbidden decays to excited bendi…
Scaling up and effective cooling of ions in surface ion trap are central challenges in quantum computing and quantum simulation with trapped ions. In this theoretical study, we propose a versatile surface ion trap. In the manipulation zone of our trap, a symmetric seven-wire geometry enables innate principle-axes rotation of two parallel linear ion chains, which facilitates the cooling of ions along all principle trap axes. To alleviate contaminating the manipulation zone during ion loading, a symmetric five-wire geometry is designed as the loading zone. And a "fork junction" connects the load…
We have realized a one dimensional optical lattice for individual atoms with a lifetime >300 s, which is 5 times longer than previously reported. In order to achieve this long lifetime, it is necessary to laser cool the at-oms briefly every 20 s to overcome heating due to technical fluctuations in the trapping potential. Without cooling, we observe negligible atom loss within the first 20 s followed by an exponential decay with a 62 s time constant. We obtain quantitative agreement with the measured fluctuations of the trapping potential and the corresponding theoretical heating rates.
Ultracold CH radicals promise a fruitful testbed for probing quantum-state controllable organic chemistry. In this work, we calculate CH vibrational branching ratios (VBRs) and rotational branching ratios (RBRs) with ground state mixing. We subsequently use these values to inform optical cycling proposals and consider two possible radiative cooling schemes using the $X^{2}Π\leftarrow A^{2}Δ$ and $X^{2}Π\leftarrow B^{2}Σ^{-}$ transitions. As a first step towards laser cooled CH, we characterize the effective buffer gas cooling of this species and produce $\sim5\times10^{10}$ CH molecules per pu…
We report an experimental study of peak and phase-space density of a two-stage magneto-optical trap (MOT) of 6-Li atoms, which exploits the narrower $2S_{1/2}\rightarrow 3P_{3/2}$ ultra-violet (UV) transition at 323 nm following trapping and cooling on the more common D2 transition at 671 nm. The UV MOT is loaded from a red MOT and is compressed to give a high phase-space density up to $3\times 10^{-4}$. Temperatures as low as 33 $μ$K are achieved on the UV transition. We study the density limiting factors and in particular find a value for the light-assisted collisional loss coefficient of $1…
We present experimental results from a new scheme for magneto-optically trapping strontium monofluoride (SrF) molecules, which provides increased confinement compared to our original work. The improved trap employs a new approach to magneto-optical trapping presented by M. Tarbutt, \emph{arXiv preprint} 1409.0244, which provided insight for the first time into the source of the restoring force in magneto-optical traps (MOTs) where the cycling transition includes dark Zeeman sublevels (known as type-II MOTs). We measure a radial spring constant $20\times$ greater than in our original work with …
We investigate how the nonlinearity of the Zeeman shift for strong magnetic fields affects the dynamics of rf field induced evaporative cooling in magnetic traps. We demonstrate for the 87-Rb and 23-Na F=2 trapping states with wave packet simulations how the cooling stops when the rf field frequency goes below a certain limit (for the 85-Rb F=2 trapping state the problem does not appear). We examine the applicability of semiclassical models for the strong field case as an extension of our previous work [Phys. Rev. A 58, 3983 (1998)]. Our results verify many of the aspects observed in a recent …
We present a high-power tunable deep-ultraviolet (DUV) laser that uses two consecutive cavity enhanced doubling stages with LBO and CLBO crystals to produce the fourth harmonic of an amplified homebuilt external cavity diode laser. The system generates up to 2.75 W of 261.5 nm laser light with a ~2 W stable steady-state output power and performs second harmonic generation in a largely unexplored high intensity regime in CLBO for continuous wave DUV light. We use this laser to perform fluorescence spectroscopy on the $X^1Σ\leftarrow A^1Π$ transition in a cold, slow beam of AlCl molecules and pr…
Laser cooling and magneto-optical trapping of molecules typically involves multiple transitions driven by several laser frequencies. We analyze how magneto-optical trapping forces depend on the angular momenta, $F_l$ and $F_u$, and the g-factors, $g_l$ and $g_u$, of the lower and upper states. When $F_l > F_u$ the polarizations must be reversed relative to cases where $F_u \ge F_l$. The correct choice of circular polarization depends on the sign of $g_{u}$ but not on the sign of $g_{l}$. If $g_{u}$ is zero there is no trapping force, and the trapping force is very weak whenever $g_u$ is small …
The direct photodissociation of trapped $^{85}$Rb$_2^+$ (rubidium) molecular ions by the cooling light for the $^{85}$Rb magneto-optical trap (MOT) is studied, both experimentally and theoretically. Vibrationally excited Rb$_{2}^{+}$ ions are created by photoionization of Rb$_{2}$ molecules formed photoassociatively in the Rb MOT and are trapped in a modified spherical Paul trap. The decay rate of the trapped Rb$_{2}^{+}$ ion signal in the presence of the MOT cooling light is measured and agreement with our calculated rates for molecular ion photodissociation is observed. The photodissociation…
High-power and narrow-linewidth laser light is a vital tool for atomic physics, being used for example in laser cooling and trapping and precision spectroscopy. Here we produce Watt-level laser radiation at 457.49 nm and 460.86 nm of respective relevance for the cooling transitions of cadmium and strontium atoms. This is achieved via the frequency doubling of a kHz-linewidth vertical-external-cavity surface-emitting laser (VECSEL), which is based on a novel gain chip design enabling lasing at > 2 W in the 915-928 nm region. Following an additional doubling stage, spectroscopy of the $^1S_0\to{…
We demonstrate the trapping and manipulation of single neutral atoms in reconfigurable arrays of optical tweezers. Our approach offers unparalleled speed by using a Texas Instruments Digital Micro-mirror Device (DMD) as a holographic amplitude modulator with a frame rate of 20,000 per second. We show the trapping of static arrays of up to 20 atoms, as well as transport of individually selected atoms over a distance of 25μm with laser cooling and 4μm without. We discuss the limitations of the technique and the scope for technical improvements.
We demonstrate loading of SrF molecules into an optical dipole trap (ODT) via in-trap $Λ$-cooling. We find that this cooling can be optimized by a proper choice of relative ODT and $Λ$ beam polarizations. In this optimized configuration, we observe molecules with temperatures as low as 14(1) $μ$K in traps with depths up to 570 $μ$K. With optimized parameters, we transfer $\!\sim\!5$% of molecules from our radio-frequency magneto-optical trap into the ODT, at a density of $\sim\!2\times 10^{9}$ cm$^{-3}$, a phase space density of $\sim\!2\times 10^{-7}$, and with a trap lifetime of $\!\sim\!1$ …
We demonstrate simultaneous deceleration and trapping of a cold atomic and molecular mixture. This is the first step towards studies of cold atom-molecule collisions at low temperatures as well as application of sympathetic cooling. Both atoms and molecules are cooled in a supersonic expansion and are loaded into a moving magnetic trap which brings them to rest via the Zeeman interaction from an initial velocity of 375 m/s. We use a beam seeded with molecular Oxygen, and entrain it with Lithium atoms by laser ablation prior to deceleration. The deceleration ends with loading of the mixture int…
Precision optical spectroscopy of exotic ions reveals accurate information about nuclear properties such as charge radii and magnetic and quadrupole moments. Thorium ions exhibit unique nuclear properties with high relevance for testing symmetries of nature. We report loading and trapping of single $^{232}$Th$^+$ ions in a linear Paul trap, embedded into and sympathetically cooled by small crystals of trapped $^{40}$Ca$^+$ ions. Trapped Th ions are identified in a non-destructive manner from the voids in the laser-induced Ca fluorescence pattern emitted by the crystal, and alternatively, by me…
A planar triplet of diffraction gratings is used to transform a single laser beam into a four-beam tetrahedral magneto-optical trap. This `flat' pyramid diffractor geometry is ideal for future microfabrication. We demonstrate the technique by trapping and subsequently sub-Doppler cooling 87Rb atoms to 30microKelvin.
We confine 4 10^8 fermionic 6Li atoms simultaneously with 9 10^9 bosonic 7Li atoms in a magneto-optical trap based on an all-semiconductor laser system. We optimize the two-isotope sample for sympathetic evaporative cooling. This is an essential step towards the production of a quantum-degenerate gas of fermionic lithium atoms.
We demonstrate a Magneto-Optical Trap (MOT) configuration which employs optical forces due to light scattering between electronically excited states of the atom. With the standard MOT laser beams propagating along the {\it x}- and {\it y}- directions, the laser beams along the {\it z}-direction are at a different wavelength that couples two sets of {\it excited} states. We demonstrate efficient cooling and trapping of cesium atoms in a vapor cell and sub-Doppler cooling on both the red and blue sides of the two-photon resonance. The technique demonstrated in this work may have applications in …
