The ability to cool atoms below the Doppler limit -- the minimum temperature reachable by Doppler cooling -- has been essential to most experiments with quantum degenerate gases, optical lattices and atomic fountains, among many other applications. A broad set of new applications await ultracold molecules, and the extension of laser cooling to molecules has begun. A molecular magneto-optical trap has been demonstrated, where molecules approached the Doppler limit. However, the sub-Doppler temperatures required for most applications have not yet been reached. Here we cool molecules to 50 uK, well below the Doppler limit, using a three-dimensional optical molasses. These ultracold molecules could be loaded into optical tweezers to trap arbitrary arrays for quantum simulation, launched into a molecular fountain for testing fundamental physics, and used to study ultracold collisions and ultracold chemistry.
We report on observations of thermal motion of a single, Doppler-cooled ion along the axis of a linear radio-frequency quadrupole trap. We show that for a harmonic potential the thermal occupation of energy levels leads to Gaussian distribution of the ion's axial position. The dependence of the spatial thermal spread on the trap potential is used for precise calibration of our imaging system's point spread function and sub-milliKelvin thermometry. We employ this technique to investigate the laser detuning dependence of the Doppler temperature.
A counterintuitive scheme to produce ultracold hydrogen via fragmentation of laser cooled diatomic hydrides is presented where the final atomic H temperature is inversely proportional to the mass of the molecular parent. In addition, the critical density for formation of a Bose-Einstein Condensate (BEC) at a fixed temperature is reduced by a factor ratio hydrogen mass: parent mass raised to power 3/2 over directly cooled hydrogen atoms. The narrow Feshbach resonances between a singlet S atom and hydrogen are well suited to a tiny center of mass energy release necessary during fragmentation. Wi…
We report Monte Carlo wave function simulation results on cold collisions between magnesium atoms in a strong red-detuned laser field. This is the normal situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We find that radiative heating does not seem to affect the Doppler limit in this case. We also describe a channelling mechanism due to the missing Q branch in the excitation scheme, which could lead to a suppress…
We demonstrate Doppler-free saturated absorption spectroscopy of cold molecular radicals formed by laser ablation inside a cryogenic buffer gas cell. By lowering the temperature, congested regions of the spectrum can be simplified, and by using different temperatures for different regions of the spectrum a wide range of rotational states can be studied optimally. We use the technique to study the optical spectrum of YbF radicals with a resolution of 30 MHz, measuring the magnetic hyperfine parameters of the electronic ground state. The method is suitable for high resolution spectroscopy of a g…
We demonstrate one-dimensional Doppler cooling of a beam of buffer-gas cooled Barium monofluoride (BaF) molecules. The dependences of the cooling efficiency with the laser detuning, the bias filed and the laser intensity are carefully measured. We numerical simulate our experiment with a Monte Carlo method, and find the theoretic predictions consists with our experimental data. This result represents a key step towards further cooling and trapping of BaF molecules.
The last few years have seen rapid progress in the application of laser cooling to molecules. In this review, we examine what kinds of molecules can be laser cooled, how to design a suitable cooling scheme, and how the cooling can be understood and modelled. We review recent work on laser slowing, magneto-optical trapping, sub-Doppler cooling, and the confinement of molecules in conservative traps, with a focus on the fundamental principles of each technique. Finally, we explore some of the exciting applications of laser-cooled molecules that should be accessible in the near term.
We report laser cooling and trapping of yttrium monoxide (YO) molecules in an optical lattice. We show that gray molasses cooling remains exceptionally efficient for YO molecules inside the lattice with a molecule temperature as low as 6.1(6) $μ$K. This approach has produced a trapped sample of 1200 molecules, with a peak spatial density of $\sim1.2\times10^{10}$ cm$^{-3}$, and a peak phase-space density of $\sim3.1\times10^{-6}$. By adiabatically ramping down the lattice depth, we cool the molecules further to 1.0(2) $μ$K, twenty times colder than previously reported for laser-cooled molecule…
We demonstrate coherent microwave control of the rotational, hyperfine and Zeeman states of ultracold CaF molecules, and the magnetic trapping of these molecules in a single, selectable quantum state. We trap about $5\times 10^{3}$ molecules for 2 s at a temperature of 65(11) $μ$K and a density of $1.2 \times 10^{5}$ cm$^{-3}$. We measure the state-specific loss rate due to collisions with background helium.
We have performed for the first time direct laser spectroscopy of the 1S0-3P0 optical clock transition at 265.6 nm in fermionic isotopes of neutral mercury laser-cooled in a magneto-optical trap. Spectroscopy is performed by measuring the depletion of the magneto-optical trap induced by the excitation of the long-lived 3P0 state by a probe at 265.6 nm. Measurements resolve the Doppler-free recoil doublet allowing for a determination of the transition frequency to an uncer- tainty well below the Doppler-broadened linewidth. We have performed absolute measurement of the frequency with respect to…
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…
A novel two-stage helium buffer gas cooled beam source is introduced. The properties of the molecular beams produced from this source are investigated theoretically using the CaF as a test molecule. The gas-phase molecules are first produced inside a 3~K helium buffer gas cell by laser ablation and subsequently cooled down to 3~K by collisions with buffer gas atoms. The precooled molecules are then extracted into the 0.5~K helium buffer gas cell where they are cooled further down to 0.5~K by collisions with cold helium atoms. Finally, the cold molecules are extracted out into the high vacuum t…
We report the design and experimental demonstration of a compact, reconfigurable Penning ion trap constructed with rare-earth permanent magnets placed outside of a trap vacuum enclosure. We describe the first observation of Doppler laser cooling of ions in a permanent magnet Penning trap. We detail a method for quantifying and optimizing the trap magnetic field uniformity in situ using a thermal beam of neutral $^{40}$Ca precursor atoms. Doppler laser cooling of $^{40}$Ca$^+$ is carried out at 0.65~T, and side-view images of trapped ion fluorescence show crystalline order for both two- and thr…
Efficient self-interference of single-photons emitted by a sideband-cooled Barium ion is demonstrated. First, the technical tools for performing efficient coupling to the quadrupolar transition of a single $^{138}$Ba$^{+}$ ion are presented. We show efficient Rabi oscillations of the internal state of the ion using a highly stabilized 1.76 $μm$ fiber laser resonant with the S$_{1/2}$-D$_{5/2}$ transition. We then show sideband cooling of the ion's motional modes and use it as a means to enhance the interference contrast of the ion with its mirror-image to up to 90%. Last, we measure the depend…
We report the successful buffer-gas cooling and magnetic trapping of chromium atoms with densities exceeding $10^{12}$ atoms per cm$^{3}$ at a temperature of 350 mK for the trapped sample. The possibilities to extend the method to buffer-gas cool and magnetically trap molecules are discussed. To minimize the most important loss mechanism in magnetic trapping, molecules with a small spin-spin interaction and a large rotational constant are preferred. Both the CrH ($^6Σ^+$ ground state) and MnH ($^7Σ^+$) radicals appear to be suitable systems for future experiments.
Barium monohydride (BaH) is an attractive candidate for extending laser cooling and trapping techniques to diatomic hydrides. The apparatus and high-resolution optical spectroscopy presented here demonstrate progress toward this goal. A cryogenic buffer-gas-cooled molecular beam of BaH was constructed and characterized. Pulsed laser ablation into cryogenic helium buffer gas delivers $\sim1\times10^{10}$ molecules/sr/pulse in the X$^2Σ^+$ ($v''=0,N''=1$) state of primary interest. More than $1\times10^7$ of these molecules per pulse enter the downstream science region with forward velocities be…
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 present the first demonstration of an inertially sensitive atomic interferometer based on a continuous, rather than pulsed, atomic beam at sub-Doppler temperatures in three dimensions. We demonstrate 30\% fringe contrast in continuous, inertially sensitive interference fringes at interrogation time $T=6.7~\mathrm{ms}$ and a short-term phase measurement noise of $530~\mathrm{μrad /\sqrt{Hz}}$ as inferred from interference measurements. Atoms are delivered to the interferometer by a cold-rubidium source that produces a high flux of atoms at temperature $\leq15~\mathrmμ K$ in three dimensions …
Experimental techniques to manipulate cold molecules have seen great development in recent years. The precision measurements of cold molecules are expected to give insights into fundamental physics. We use a rovibrationally pure sample of ultracold KRb molecules to improve the measurement on the stability of electron-to-proton mass ratio ($μ= \frac{m_{\rm e}}{M_{\rm p}}$). The measurement is based upon a large sensitivity coefficient of the molecular spectroscopy, which utilizes a transition between nearly a degenerate pair of vibrational levels each associated with a different electronic pote…
Doppler and Sisyphus cooling of $^{174}$YbOH are achieved and studied. This polyatomic molecule has high sensitivity to physics beyond the Standard Model and represents a new class of species for future high-precision probes of new T-violating physics. The transverse temperature of the YbOH beam is reduced by nearly two orders of magnitude to $< 600 \, μ$K and the phase-space density is increased by a factor of $>6$ via Sisyphus cooling. We develop a full numerical model of the laser cooling of YbOH and find excellent agreement with the data. We project that laser cooling and magneto-optical t…
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…
Analogous to the extension of laser cooling techniques from two-level to three-level atoms, Doppler cooling of molecules with an intermediate electronic state is considered. In particular, we use a rate-equation approach to simulate cooling of SiO+, in which population buildup in the intermediate state is prevented by its short lifetime. We determine that Doppler cooling of SiO+ can be accomplished without optically repumping from the intermediate state, at the cost of causing undesirable parity flips and rotational diffusion. Since the necessary repumping would require a large number of conti…
Recently, laser cooling methods have been extended from atoms to molecules. The complex rotational and vibrational energy level structure of molecules makes laser cooling difficult, but these difficulties have been overcome and molecules have now been cooled to a few microkelvin and trapped for several seconds. This opens many possibilities for applications in quantum science and technology, controlled chemistry, and tests of fundamental physics. This article explains how molecules can be decelerated, cooled and trapped using laser light, reviews the progress made in recent years, and outlines…
Specular reflection of polar molecules from a simple multi-cylinder electrostatic mirror: a method for separating BaF molecules produced in a buffer-gas-cooled laser-ablation source from other ablation products
We reported a detailed experimental study of the cold collision of Barium monofluoride (BaF) with buffer gas and the high-resolution spectroscopy relevant with direct laser cooling. BaF molecules are efficiently produced with laser ablation and buffer-gas cooled in a cryogenic apparatus. The laser cooling relevant transition $|X^2Σ, v=0, N=1\rangle$ to $|A^2Π, v'=0, J'=1/2\rangle$ is identified. The collision cross section with buffer gas is measured to be $1.4(7)\times10^{-14} cm^{-2}$, which is very suitable for buffer gas cooling. Both rotational and vibrational temperatures are effectively…
We report on the direct conversion of laser-cooled 41K and 87Rb atoms into ultracold 41K87Rb molecules in the rovibrational ground state via photoassociation followed by stimulated Raman adiabatic passage. High-resolution spectroscopy based on the coherent transfer revealed the hyperfine structure of weakly bound molecules in an unexplored region. Our results show that a rovibrationally pure sample of ultracold ground-state molecules is achieved via the all-optical association of laser-cooled atoms, opening possibilities to coherently manipulate a wide variety of molecules.
We report an experimental investigation on the Doppler-free saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride (BaF) molecules in a 4~K cryogenic cell. The obtained spectra with a resolution of 19~MHz, much smaller than previously observed in absorption spectroscopy, clearly resolve the hyperfine transitions. Moreover, we use these high-resolution spectra to fit the hyperfine splittings of excited $A(v=0)$ state and find the hyperfine splitting of the laser-cooling-relevant $A^2Π_{1/2}(v=0, J=1/2, +)$ state is about 18 MHz, much higher than the previous theoretically pr…
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 may be 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~$μ$m antisymmetric Re=O stretching mode of MTO with a resolution of 8~MHz and a frequency accuracy of 30~MHz. We partial…
Gas-phase multiply charged proteins have been sympathetically cooled to translational temperatures below 1 K by Coulomb interaction with laser-cooled barium ions in a linear ion trap. In one case, an ensemble of 53 cytochrome c molecules (mass ~ 12390 amu, charge +17 e) was cooled by ~ 160 laser-cooled barium ions to less than 0.75 K. Storage times of more than 20 minutes have been observed and could easily be extended to more than an hour. The technique is applicable to a wide variety of complex molecules.
Calcium monofluoride (CaF) molecules are loaded into an optical dipole trap (ODT) and subsequently laser cooled within the trap. Starting with magneto-optical trapping, we sub-Doppler cool CaF and then load $150(30)$ CaF molecules into an ODT. Enhanced loading by a factor of five is obtained when sub-Doppler cooling light and trapping light are on simultaneously. For trapped molecules, we directly observe efficient sub-Doppler cooling to a temperature of $60(5)$ $μ\text{K}$. The trapped molecular density of $8(2)\times10^7$ cm$^{-3}$ is an order of magnitude greater than in the initial sub-Dop…
Precision searches for time-reversal symmetry violating interactions in polar molecules are extremely sensitive probes of high energy physics beyond the Standard Model. To extend the reach of these probes into the PeV regime, long coherence times and large count rates are necessary. Recent advances in laser cooling of polar molecules offer one important tool -- optical trapping. However, the types of molecules that have been laser-cooled so far do not have the highly desirable combination of features for new physics searches, such as the ability to fully polarize and the existence of internal …
An improved system for creating a pulsed, low-temperature molecular beam of OH radicals has been developed. We use a pulsed discharge to create OH from H$_2$O seeded in Xe during a supersonic expansion, where the high-voltage pulse duration is significantly shorter than the width of the gas pulse. The pulsed discharge allows for control of the mean speed of the molecular packet as well as maintains a low temperature supersonic expansion. A hot filament is placed in the source chamber to initiate the discharge for shorter durations and at lower voltages, resulting in a translationally and rotat…
We show that a large class of helium-containing cold polar molecules form readily in a cryogenic buffer gas, achieving densities as high as 10^12 cm^-3. We explore the spin relaxation of these molecules in buffer gas loaded magnetic traps, and identify a loss mechanism based on Landau-Zener transitions arising from the anisotropic hyperfine interaction. Our results show that the recently observed strong T^6 thermal dependence of spin change in buffer gas trapped silver (Ag) is accounted for by the formation and spin change of AgHe, thus providing evidence for molecular formation in a buffer ga…
We describe a simple approach to the problem of incorporating the response time of an atom or ion being Doppler-cooled into the theory of the cooling process. The system being cooled does not in general respond instantly to the changing laser frequencies it experiences in its rest frame, and this "dynamic effect" can affect significantly the temperatures attainable. It is particularly important for trapped ions when there is a slow decay out of the cooling cycle requiring the use of a repumping beam. We treat the cases of trapped ions with two and three internal states, then apply the theory t…
We demonstrate one-dimensional sub-Doppler laser cooling of a beam of YbF molecules to 100 $μ$K. This is a key step towards a measurement of the electron's electric dipole moment using ultracold molecules. We compare the effectiveness of magnetically-assisted and polarization-gradient sub-Doppler cooling mechanisms. We model the experiment and find good agreement with our data.
Cold collisions of $^{14}$N$^{16}$O molecules in the $^{2}Π_{1/2}$ ground state, subject to electric and magnetic fields, are investigated. It is found that elastic collision rates significantly exceed state-changing inelastic rates only at temperatures above 0.5 K at laboratory strength fields. It is found, however, that in very large fields $> 10^{4}$ V/cm, inelastic rates can be somewhat suppressed. Magnetic fields have negligible influence on scattering for this nearly non-magnetic state.
We explore the possibilities for a next-generation electron-electric-dipole-moment experiment using ultracold heteronuclear diatomic molecules assembled from a combination of radium and another laser-coolable atom. In particular, we calculate their ground state structure and their sensitivity to parity- and time-reversal (${\cal{P,T}}$) violating physics arising from flavor-diagonal charge-parity (${\cal{CP}}$) violation. Among these species, the largest ${\cal{P,T}}$-violating molecular interaction constants -- associated for example with the electron electric dipole moment -- are obtained fo…
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…
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 …
Weak transitions in the (2,0) overtone band of the HD molecule at $λ= 1.38 \, μ$m were measured in saturated absorption using the technique of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Narrow Doppler-free lines were interrogated with a spectroscopy laser locked to a frequency comb laser referenced to an atomic clock to yield transition frequencies [R(1) = $217\,105\,181\,895\,(20)$ kHz; R(2) = $219\,042\,856\,621\,(28)$ kHz; R(3) = $220\,704\,304\,951\,(28)$ kHz] at three orders of magnitude improved accuracy. These benchmark values provide a test of QED in the sm…
We report on the realization of sub-Doppler laser cooling of sodium atoms in gray molasses using the D1 optical transition ($3s\, ^2S_{1/2} \rightarrow 3p\, ^2P_{1/2}$) at 589.8 nm. The technique is applied to samples containing $3\times10^9$ atoms, previously cooled to 350 $μ$K in a magneto-optical trap, and it leads to temperatures as low as 9 $μ$K and phase-space densities in the range of $10^{-4}$. The capture efficiency of the gray molasses is larger than 2/3, and we observe no density-dependent heating for densities up to $10^{11}$ cm$^{-3}$.
We present a practical roadmap to achieve optical cycling and laser cooling of asymmetric top molecules (ATMs). Our theoretical analysis describes how reduced molecular symmetry, as compared to diatomic and symmetric non-linear molecules, plays a role in photon scattering. We present methods to circumvent limitations on rapid photon cycling in these systems. We calculate vibrational branching ratios for a diverse set of asymmetric top molecules and find that many species within a broad class of molecules can be effectively cooled with a manageable number of lasers. We also describe methods to …
We theoretically investigate the laser cooling of fermionic barium monofluoride (137BaF) molecules, which are promising candidates for precision studies of weak parity violation and nuclear anapole moments. This molecular species features two nuclear spins, resulting in a hyperfine structure that is considerably more complicated than the one found in the usual laser-cooled diatomics. We use optical Bloch equations and rate equations to show that optical cycling, sub-Doppler cooling and bichromatic forces can all be realized under realistically achievable experimental conditions.
We have produced ultracold, polar RbCs* molecules via photoassociation in a laser-cooled mixture of Rb and Cs atoms. Using a model of the RbCs* molecular interaction which reproduces the observed rovibrational structure, we infer decay rates in our experiments into deeply bound singlet ground state RbCs vibrational levels as high as 5 x 10^5 s^-1 per level. Population in such deeply bound levels could be efficiently transferred to the vibrational ground state using a single stimulated Raman transition, opening the possibility to create large samples of stable, ultracold polar molecules.
We demonstrate sub-Doppler laser cooling of $ ^{39} $K using degenerate Raman sideband cooling via the 4S$_{1/2} \rightarrow $5P$ _{1/2} $ transition at 404.8 nm. By using an optical lattice in combination with a magnetic field and optical pumping beams, we obtain a spin-polarized sample of up to $5.6 \times 10^{7}$ atoms cooled down to a sub-Doppler temperature of 4 $μ$K, reaching a peak density of $3.9 \times 10^{9}$ atoms/cm$ ^{3} $, a phase-space density greater than $ 10^{-5} $, and an average vibrational level of $ \langle ν\rangle=0.6 $ in the lattice. This work opens up the possibility…
Calcium monofluoride (CaF) is magnetically slowed and trapped using optical pumping. Starting from a collisionally cooled slow beam, CaF with an initial velocity of ~ 30 m/s is slowed via magnetic forces as it enters a 800 mK deep magnetic trap. Employing two-stage optical pumping, CaF is irreversibly loaded into the trap via two scattered photons. We observe a trap lifetime exceeding 500 ms, limited by background collisions. This method paves the way for cooling and magnetic trapping of chemically diverse molecules without closed cycling transitions.
Magneto-optical traps (MOTs) of Er and Dy have recently been shown to exhibit population-wide sub-Doppler cooling due to their near degeneracy of excited and ground state Lande g factors. We discuss here an additional, unusual intra-MOT sub-Doppler cooling mechanism that appears when the total Dy MOT cooling laser intensity and magnetic quadrupole gradient increase beyond critical values. Specifically, anisotropically sub-Doppler-cooled cores appear, and their orientation with respect to the quadrupole axis flips at a critical ratio of the MOT laser intensity along the quadrupole axis versus t…
We demonstrate a scheme for magneto-optically trapping strontium monofluoride (SrF) molecules at temperatures one order of magnitude lower and phase space densities three 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…
We propose an experiment to measure the electric dipole moment of the electron using ultracold YbF molecules. The molecules are produced as a thermal beam by a cryogenic buffer gas source, and brought to rest in an optical molasses that cools them to the Doppler limit or below. The molecular cloud is then thrown upward to form a fountain in which the electric dipole moment of the electron is measured.
The accurate evaluation of the second-order Doppler frequency shift (SODFS) of trapped ions in a linear Paul trap has been studied with experiments and molecular dynamics (MD) simulations. The motion of trapped ions in the trap has three contributions, and we focus on the ion excess micromotion, which is rarely discussed when evaluating the SODFS. Based on the hypothesis that the ion density is uniformly distributed in the radial direction, we propose a new model to accurately evaluate the total SODFS for ion microwave clocks. The effectiveness of the model has been verified both in simulation…
We demonstrate full quantum state control of two species of single atoms using optical tweezers and assemble the atoms into a molecule. Our demonstration includes 3D ground-state cooling of a single atom (Cs) in an optical tweezer, transport by several microns with minimal heating, and merging with a single Na atom. Subsequently, both atoms occupy the simultaneous motional ground state with 61(4)\% probability. This realizes a sample of exactly two co-trapped atoms near the phase-space-density limit of one, and allows for efficient stimulated-Raman transfer of a pair of atoms into a molecular …
