Stark deceleration allows for precise control over the velocity of a pulsed molecular beam and, by the nature of its limited phase-space acceptance, reduces the energy width of the decelerated packet. We describe an alternate method of operating a Stark decelerator that further reduces the energy spread over the standard method of operation. In this alternate mode of operation, we aggressively decelerate the molecular packet using a high phase angle. This technique brings the molecular packet to the desired velocity before it reaches the end of the decelerator; the remaining stages are then used to longitudinally and transversely guide the packet to the detection/interaction region. The result of the initial aggressive slowing is a reduction in the phase-space acceptance of the decelerator and thus a narrowing of the velocity spread of the molecular packet. In addition to the narrower energy spread, this method also results in a velocity spread that is nearly independent of the final velocity. Using the alternate deceleration technique, the energy resolution of molecular collision measurements can be improved considerably.
We present a study of vibrational quenching and chemical processes of molecular ions immersed in an ultracold atomic gas by means of the quasi-classical trajectory (QCT) method. In particular, BaRb$^+(v)$ + Rb collisions are studied at cold temperatures revealing a highly efficient energy transfer between the translational degrees of freedom and internal degrees of the molecular ion. Thus leading to a large vibrational quenching cross section which follows the Langevin capture model prediction. These results play a key role on the understanding of relaxation phenomena of cold molecular ions in…
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 bet…
We report the sympathetic cooling and Coulomb crystallization of molecular ions above the surface of an ion-trap chip. N$_2^+$ and CaH$^+$ ions were confined in a surface-electrode radiofrequency ion trap and cooled by the interaction with laser-cooled Ca$^{+}$ ions to secular translational temperatures in the millikelvin range. The configuration of trapping potentials generated by the surface electrodes enabled the formation of planar bicomponent Coulomb crystals and the spatial separation of the molecular from the atomic ions on the chip. The structural and thermal properties of the Coulomb …
Stereodynamic control of resonant molecular collisions has emerged as a new frontier in cold molecule research. Recent experimental studies have focused on weakly interacting molecular systems such as HD collisions with H$_2$, D$_2$ and He. We report here the possibility of such control in strongly interacting systems taking rotational relaxation in cold collisions of HCl and H$_2$. Using explicit quantum scattering calculations in full six dimensions it is shown that robust control of the collision dynamics is possible even when multiple (overlapping) shape-resonances coexist in a narrow ener…
We discuss theoretically ion-atom collisions at low energy and predict the possibility of formation of cold molecular ion by photoassociation. We present results on radiative homo- and hetero-nuclear atom-ion cold collisions that reveal threshold behaviour of atom-ion systems.
We present a realistic molecular-dynamics treatment of laser-cooled ions in radiofrequency ion traps which avoids previously made simplifications such as modeling laser cooling as a friction force and combining individual heating mechanisms into a single effective heating force. Based on this implementation, we show that infrequent energetic collisions of single ions with background gas molecules lead to pronounced heating of the entire ion ensemble and a time-varying secular ensemble temperature which manifests itself in a superstatistical time-averaged velocity distribution of the ions. The …
Cold, velocity-controlled molecular beams consisting of a single quantum state promise to be a powerful tool for exploring molecular scattering interactions. In recent years, Stark deceleration has emerged as one of the main methods for producing velocity-controlled molecular beams. However, Stark deceleration is shown not to be effective at producing a molecular beam consisting of a single quantum state in many circumstances. Therefore, quantum state purity must be carefully considered when using Stark decelerated beams, particularly in collision experiments where contributions from all quant…
We show that multichannel quantum defect theory (MQDT) can be applied successfully as an efficient computational method for cold molecular collisions in Li+NH, which has a deep and strongly anisotropic interaction potential. In this strongly coupled system, closed-channel poles restrict the range over which the MQDT Y matrix can be interpolated. We present an improved procedure to transform the MQDT reference functions so that the poles are removed from the energy range of interest. Effects due to very long-range spin-dipolar couplings are outside the scope of MQDT, but can be added perturbati…
A method for decelerating a continuous beam of neutral polar molecules is theoretically demonstrated. This method utilizes non-uniform, static electric fields and regions of adiabatic population transfer to generate a mechanical force that opposes the molecular beam's velocity. By coupling this technique with dissipative trap-loading, molecular densities $\geq10^{11}$ cm$^{-3}$ are possible. When used in combination with forced evaporative cooling the proposed method may represent a viable route to quantum degeneracy for a wide-class of molecular species.
Intense beams of cold and slow molecules are produced by supersonic expansion out of a rapidly rotating nozzle, as first demonstrated by Gupta and Herschbach. An improved setup is presented that allows to accelerate or decelerate cold atomic and molecular beams by up to 500 m/s. Technical improvements are discussed and beam parameters are characterized by detailed analysis of time of flight density distributions. The possibility of combining this beam source with electrostatic fields for guiding polar molecules is demonstrated.
We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applicatio…
A recent expansion of cold and ultracold molecule applications has led to renewed focus on molecular species preparation under ultrahigh vacuum conditions. Meanwhile, molecular beams have been used to study gas phase chemical reactions for decades. In this manuscript, we describe an apparatus that uses pulsed molecular beam technology to achieve high local gas densities, leading to faster reaction rates with cold trapped ions. We characterize the beam's spatial profile using the trapped ions themselves. This apparatus could be used for preparation of molecular species by reactions requiring ex…
We report a study of cold charge-transfer (CT) collisions of Rb atoms with N$_2^+$ and O$_2^+$ ions in the mK regime using a dynamic ion-neutral hybrid trapping experiment. State- and collision-energy- dependent reaction rate coefficients have been measured for both systems. We observe markedly different charge-transfer kinetics and dynamics for the different systems and reaction channels. While the kinetics in some channels are consistent with classical capture theory for the rate coefficient, others show distinct non-universal dynamics. The experimental results are interpreted with the help …
Molecular collisions can be studied at very low relative kinetic energies, in the milliKelvin range, by merging codirectional beams with much higher translational energies, extending even to the kiloKelvin range, provided that the beam speeds can be closely matched. This technique provides far more intensity and wider chemical scope than methods that require slowing both collision partners. Previously, at far higher energies, merged beams have been widely used with ions and/or neutrals formed by charge transfer. Here we assess for neutral, thermal molecular beams the range and resolution of co…
This paper presents detailed characteristics of an ultra-cold bright metastable neon atomic beam which we have been using for atom-interferometric applications. The basis of the device is an atomic beam released from a magneto-optical trap (MOT) which is operated with a high intensity trapping laser, high magnetic quadrupole field, and large laser detuining. Mainly due to the complex structure of three dimensional magnetic field and laser beams, a bright small spot of atoms is formed near the center of the quadrupole magnetic field under an appropriate operating condition. We obtained the mini…
The potential energy curves, permanent and transition dipole moments, and the static dipolar polarizability, of molecular ions composed of one alkali-metal atom and a Strontium ion are determined with a quantum chemistry approach. The molecular ions are treated as effective two-electron systems and are treated using effective core potentials including core polarization, large gaussian basis sets, and full configuration interaction. In the perspective of upcoming experiments aiming at merging cold atom and cold ion traps, possible paths for radiative charge exchange, photoassociation of a cold …
We report bunching, slowing, and acceleration of a supersonically cooled beam of diatomic hydroxyl radicals (OH). \textit{In situ} observation of laser-induced fluorescence along the beam propagation path allows for detailed characterization of longitudinal phase-space manipulation of OH molecules through the Stark effect by precisely sequenced inhomogeneous electric fields.
In this theoretical work, we calculate potential energy curves, spectroscopic pa- rameters and transition dipole moments of molecular ions BeX^+ (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarization potentials, and full configuration interaction (CI). We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion-atom colliding systems by stimu- lated Raman adiabatic p…
We use recently developed angulon theory [Phys. Rev. Lett. 114, 203001 (2015)] to study the rotational spectrum of a cyanide molecular anion immersed into Bose-Einstein condensates of rubidium and strontium. Based on $\textit {ab initio}$ potential energy surfaces, we provide a detailed study of the rotational Lamb shift and many-body-induced fine structure which arise due to dressing of molecular rotation by a field of phonon excitations. We demonstrate that the magnitude of these effects is large enough in order to be observed in modern experiments on cold molecular ions. Furthermore, we int…
We demonstrate and characterize a cryogenic buffer gas-cooled molecular beam source capable of producing bright beams of free radicals and refractory species. Details of the beam properties (brightness, forward velocity distribution, transverse velocity spread, rotational and vibrational temperatures) are measured under varying conditions for the molecular species SrF. Under typical conditions we produce a beam of brightness 1.2 x 10^11 molecules/sr/pulse in the rovibrational ground state, with 140 m/s forward velocity and a rotational temperature of approximately 1 K. This source compares fav…
In the past two decades, the revolutionary technologies of creating cold and ultracold molecules have provided cutting-edge experiments for studying the fundamental phenomena of collision physics. To a large degree, the recent explosion of interest in the molecular collisions has been sparked by dramatic progress of experimental capabilities and theoretical methods, which permit molecular collisions to be explored deep in the quantum mechanical limit. Tremendous experimental advances in the field has already been achieved, and the authors, from an experimental perspective, provide a review of …
We describe the classical two dimensinal nonlinear dynamics of cold atoms in far-off-resonant donut beams. We show that there chaotic dynamics exists for charge greater than unity, when the intensity of the beam is periodically modulated. The two dimensional distributions of atoms in $(x,y)$ plane for charge two are simulated. We show that the atoms will acumulate on several ring regions when the system enters to regime of global chaos.
We demonstrate a cryogenic buffer gas-cooled molecular beam source capable of producing bright, continuous beams of cold and slow free radicals via laser ablation over durations of up to 60~seconds. The source design uses a closed liquid helium reservoir as a large thermal mass to minimize heating and ensure reproducible beam properties during operation. Under typical conditions, the source produces beams of our test species SrF, containing $5\times10^{12}~$molecules per steradian per second in the $X^{2}Σ(v=0, N=1)$ state with a rotational temperature of $1.0(2)~$K and a forward velocity of $…
We demonstrate with a RF-MOT the one dimensional, transverse magneto-optical compression of a cold beam of calcium monofluoride (CaF). By continually alternating the magnetic field direction and laser polarizations of the magneto-optical trap, a photon scattering rate of $2π\times$0.4 MHz is achieved. A 3D model for this RF-MOT, validated by agreement with data, predicts a 3D RF-MOT capture velocity for CaF of 5 m/s.
We present an optical trap for atoms that we have developed for precision spectroscopy measurements. Cold atoms are captured in a dark region of space inside a blue-detuned hollow laser beam formed by an axicon. We analyze the light potential in a ray optics picture and experimentally demonstrate trapping of laser-cooled metastable xenon atoms.
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 properti…
We demonstrate a scheme for realizing a compact cold atom gravimeter. The use of a hollow pyramidal configuration allows to achieve all functions: trapping, interferometer and detection with a unique laser beam leading to a drastic reduction in complexity and volume. In particular, we demonstrate a relative sensitivity to acceleration of gravity (g) of 1.7 x 10-7 at one second, with a moderate laser power of 50 mW. This simple geometry combined to such a high sensitivity opens wide perspectives for practical applications (P. Bouyer and A. Landragin, patent number FR2009/000252, 2009).
We study the dynamics of neutral cold atoms in an $L$-shaped crossed-beam optical waveguide formed by two perpendicular red-detuned lasers of different intensities and a blue-detuned laser at the corner. Complemented with a vibrational cooling process this setting works as a one-way device or "atom diode".
We demonstrate a technique for producing a cold pulsed beam of atoms by transferring a cloud of atoms trapped in a three dimensional magneto-optic trap (MOT). The MOT is loaded by heating a getter source of Rb atoms. We show that it is advantageous to transfer with two beams (with a small angle between them) compared to a single beam, because the atoms stop interacting with the beams in the two-beam technique, which results in a Gaussian velocity distribution. The atoms are further cooled in optical molasses by turning off the MOT magnetic field before the transfer beams are turned on.
We report measurements on the guiding of cold $^{87}$Rb atoms from a magneto-optical trap by a continuous light beam over a vertical distance of 6.5 mm. For moderate laser power ($<$85 mW) we are able to capture around 40% of the cold atoms. Although the guide is red-detuned, the optical scattering rate at this detuning ($\approx$70 GHz) is acceptably low. For lower detuning ($<$30 GHz) a larger fraction was guided but radiation pressure starts to push the atoms upward, effectively lowering the acceleration due to gravity. The measured guided fraction agrees well with an analytical model.
We have demonstrated an atom-optical lens, with the advantage of a small scale and flexible adjustment of the parameters, realized by a far red-detuned Gaussian laser beam perpendicular to the propagation direction of the cold atomic cloud. The one-dimensional transverse focusing effect of cold atomic clouds at the temperature order of 1 $μ$K freely falling through the atom-optical lens on the micron scale have been studied theoretically and then verified experimentally. It is found that theory and experiment are in good agreement.
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^…
We discuss the design and optimisation of two types of junctions between surface-electrode radiofrequency ion-trap arrays that enable the integration of experiments with sympathetically cooled molecular ions on a monolithic chip device. A detailed description of a multi-objective optimisation procedure applicable to an arbitrary planar junction is presented, and the results for a cross junction between four quadrupoles as well as a quadrupole-to-octupole junction are discussed. Based on these optimised functional elements, we propose a multi-functional ion-trap chip for experiments with transl…
While many-particle entanglement can be found in natural solids and strongly interacting atomic and molecular gases, generating highly entangled states between weakly interacting particles in a controlled and scalable way presents a significant challenge. We describe here a one-step method to generate entanglement in a dilute gas of cold polar molecules. For molecules in optical traps separated by a few micrometers, we show that maximally entangled states can be created using the strong off-resonant pulses that are routinely used in molecular alignment experiments. We show that the resulting a…
We report the production of a continuous, slow, and cold beam of 87-Rb atoms with an unprecedented flux of 3.2 x 10^12 atoms/s and a temperature of a few milliKelvin. Hot atoms are emitted from a Rb candlestick atomic beam source and transversely cooled and collimated by a 20 cm long atomic collimator section, augmenting overall beam flux by a factor of 50. The atomic beam is then decelerated and longitudinally cooled by Zeeman slowing.
We present the preparation and deterministic delivery of a selectable number of externally cold molecular ions. A laser cooled ensemble of Mg^+ ions subsequently confined in several linear Paul traps inter-connected via a quadrupole guide serves as a cold bath for a single or up to a few hundred molecular ions. Sympathetic cooling embeds the molecular ions in the crystalline structure. MgH^+ ions, that serve as a model system for a large variety of other possible molecular ions, are cooled down close to the Doppler limit and are positioned with an accuracy of one micrometer. After the producti…
We demonstrate an atom interferometer that uses a laser-cooled continuous beam of $^{87}$Rb atoms having velocities of 10--20 m/s. With spatially separated Raman beams to coherently manipulate the atomic wave packets, Mach--Zehnder interference fringes are observed at an interference distance of 2L = 19 mm. The apparatus operates within a small enclosed area of 0.07 mm$^2$ at a bandwidth of 190 Hz with a deduced sensitivity of $7.8\times10^{-5}$ rad/s/$\sqrt{Hz}$ for rotations. Using a low-velocity continuous atomic source in an atom interferometer enables high sampling rates and bandwidths wi…
Multipole radiofrequency ion traps are a highly versatile tool to study molecular ions and their interactions in a well-controllable environment. In particular the cryogenic 22-pole ion trap configuration is used to study ion-molecule reactions and complex molecular spectroscopy at temperatures between few Kelvin and room temperatures. This article presents a tutorial on radiofrequency ion trapping in multipole electrode configurations. Stable trapping conditions and buffer gas cooling, as well as important heating mechanisms, are discussed. In addition, selected experimental studies on cation…
We demonstrate generation of an isotopically pure beam of laser-cooled Yb atoms by deflection using 1D-optical molasses. Atoms in a collimated thermal beam are first slowed using a Zeeman Slower. They are then subjected to a pair of molasses beams inclined at $45^\circ$ with respect to the slowed atomic beam. The slowed atoms are deflected and probed at a distance of 160 mm. We demonstrate selective deflection of the bosonic isotope $^{174}$Yb, and the fermionic isotope $^{171}$Yb. Using a transient measurement after the molasses beams are turned on, we find a longitudinal temperature of 41 mK…
We employ laser cooling to intensify and cool an atomic beam of metastable Ne(3s) atoms. Using several collimators, a slower and a compressor we achieve a ^{20}Ne^* flux of 6 10^{10} atoms/s in an 0.7 mm diameter beam traveling at 100 m/s, and having longitudinal and transverse temperatures of 25mK and 300microK, respectively. This constitutes the highest flux in a concentrated beam achieved to date with metastable rare gas atoms. We characterize the action of the various cooling stages in terms of their influence on the flux, diameter and divergence of the atomic beam. The brightness and bril…
This paper presents a setup capable of producing a high-flux continuous beam of cold rubidium atoms for cavity QED experiments in the regime of strong coupling. A 2 $D^+$ MOT, loaded by rubidium getters in a dry film coated vapor cell, fed a secondary moving-molasses MOT (MM-MOT) at a rate of 1.5 x $10^{10}$ atoms/sec. The MM-MOT provided a continuous beam with tunable velocity. This beam was then directed through the waist of a 280 $μ$m cavity resulting in a Rabi splitting of more than +/- 10 MHz. The presence of sufficient number of atoms in the cavity mode also enabled splitting in the pola…
We report on the transverse laser cooling of a magnetically guided beam of ultra cold chromium atoms. Radial compression by a tapering of the guide is employed to adiabatically heat the beam. Inside the tapered section heat is extracted from the atom beam by a two-dimensional optical molasses perpendicular to it, resulting in a significant increase of atomic phase space density. A magnetic offset field is applied to prevent optical pumping to untrapped states. Our results demonstrate that by a suitable choice of the magnetic offset field, the cooling beam intensity and detuning, atom losses an…
We demonstrate a high-flux and low transverse temperature atomic beam of ytterbium by applying two-dimensional cooling using the ${}^1\mathrm{S}_0\text{-}{}^3\mathrm{P}_1$ intercombination transition to the cold atomic beam produced by the dipolar-allowed ${}^1\mathrm{S}_0\text{-}{}^1\mathrm{P}_1$ transition. The optimized transverse temperature of $11 \pm 9\,\mathrm{μK}$ and an atomic flux of $(7.5 \pm 1.0) \times 10^8\,\mathrm{atoms/s}$ are obtained for the atomic beam whose longitudinal velocity is $30\,\mathrm{m/s}$. The transverse temperature is maintained below $23\,\mathrm{μK}$, while t…
We have developed a source of cold LiH molecules for Stark deceleration and trapping experiments. Lithium metal is ablated from a solid target into a supersonically expanding carrier gas. The translational, rotational and vibrational temperatures are 0.9(0.1) K, 5.9(0.5) K and 468(17) K respectively. Although they have not reached thermal equilibrium with the carrier gas, we estimate that 90% of the LiH molecules are in the ground state, X^{1} Σ^{+} (v=0, J=0). With a single 7 ns ablation pulse, the number of molecules in the ground state is 4.5(1.8)*10^{7} molecules per steradian. A second, d…
In a recent experiment [1], it was observed that a sequence of two standing wave square pulses can split a BEC at rest into +/- 2 h_bar k diffraction orders with almost 100% efficiency. By truncating the Raman-Nath equations to a 2-state model, we provide an intuitive picture that explains this double square pulse beamsplitter scheme. We further show it is possible to optimize a standingwave multi square pulse sequence to efficiently diffract an atom at rest to symmetric superposition of +/- 2n h_bar k diffraction order with n>1. The approach is considered to be qualitatively different from th…
We report on the design and characterization of a cold atom source for strontium (Sr) based on a two-dimensional magneto-optical trap (MOT) that is directly loaded from the atom jet of a dispenser. We characterize the atom flux of the source by measuring the loading rate of a three-dimensional MOT. We find loading rates of up to $10^{8}$ atoms per second. The setup is compact, easy to construct, and has low power consumption. It addresses the long standing challenge of reducing the complexity of cold beam sources for Sr, which is relevant for optical atomic clocks and quantum simulation and co…
We propose a promising scheme to decelerate a cw filtering out molecular beam using a red-detuned quasi-cw semi-Gaussian laser beam. By using Monte-Carlo simulation method, we demonstrate this optical Stark deceleration scheme, and study its decelerated dynamic process for a cw ND3 molecular beam as well as the dependence of the deceleration effect on the border width of the semi-Gaussian beam. Our study shows that the proposed scheme can be used to efficiently slow a cw ND3 molecular beam, and obtain a relative average kinetic-energy loss of 9.33% by using a single semi-Gaussian beam with a w…
Using frequency-chirped radiation pressure slowing, we precisely control the velocity of a pulsed CaF molecular beam down to a few m/s, compressing its velocity spread by a factor of 10 while retaining high intensity: at a velocity of 15~m/s the flux, measured 1.3~m from the source, is 7$\times$10$^{5}$ molecules per cm$^{2}$ 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…
Radiative emission during cold collisions between trapped laser-cooled Rb atoms and alkaline-earth ions (Ca$^+$, Sr$^+$, Ba$^+$) and Yb$^+$, and between Li and Yb$^+$, are studied theoretically, using accurate effective-core-potential based quantum chemistry calculations of potential energy curves and transition dipole moments of the related molecular ions. Radiative association of molecular ions is predicted to occur for all systems with a cross section two to ten times larger than the radiative charge transfer one. Partial and total rate constants are also calculated and compared to availabl…
