Spectroscopy of Na2 by photoassociation of laser-cooled Na

Observation of Photoassociation Resonances in Ultracold Atom-Molecule Collisions

We report on the observation of photoassociation resonances in ultracold collisions between ^{23}Na^{40}K molecules and ^{40}K atoms. We perform photoassociation in a long-wavelength optical dipole trap to form deeply bound triatomic molecules in electronically excited states. The atom-molecule Feshbach resonance is used to enhance the free-bound Franck-Condon overlap. The photoassociation into well-defined quantum states of excited triatomic molecules is identified by observing resonantly enhanced loss features. These loss features depend on the polarization of the photoassociation lasers, allowing us to assign rotational quantum numbers. The observation of ultracold atom-molecule photoassociation resonances paves the way toward preparing ground-state triatomic molecules, provides a new high-resolution spectroscopy technique for polyatomic molecules, and is also important to atom-molecule Feshbach resonances.

Modeling Photoassociative Spectra of Ultracold NaK + K

A model for photoassociation of ultracold atoms and molecules is presented and applied to the case of 39K and 23Na39K bosonic particles. The model relies on the assumption that photoassociation is dominated by long-range atom-molecule interactions well outside the chemical bond region. The frequency of the photoassociation laser is chosen close to a bound-bound rovibronic transition from the X1Σ+ ground state toward the metastable b3Π lowest excited state of 23Na39K, allowing us to neglect any other excitation, which could hinder the photoassociation detection. The energy level structure of the long-range 39K···23Na39K excited super-dimer is computed in the space-fixed frame by solving coupled-channel equations, involving the coupling between the 23Na39K internal rotation and the mechanical rotation of the super-dimer complex. A quite rich structure is obtained, and the corresponding photoassociation rates are presented. Other possible photoassociation transitions are discussed in the context of the proposed model.

Rydberg Macrodimers: Diatomic Molecules on the Micrometer Scale

Controlling molecular binding at the level of single atoms is one of the holy grails of quantum chemistry. Rydberg macrodimers─bound states between highly excited Rydberg atoms─provide a novel perspective in this direction. Resulting from binding potentials formed by the strong, long-range interactions of Rydberg states, Rydberg macrodimers feature bond lengths in the micrometer regime, exceeding those of conventional molecules by orders of magnitude. Using single-atom control in quantum gas microscopes, the unique properties of these exotic states can be studied with unprecedented control, including the response to magnetic fields or the polarization of light in their photoassociation. The high accuracy achieved in spectroscopic studies of macrodimers makes them an ideal testbed to benchmark Rydberg interactions, with direct relevance to quantum computing and information protocols where these are employed. This review provides a historic overview and summarizes the recent findings in the field of Rydberg macrodimers. Furthermore, it presents new data on interactions between macrodimers, leading to a phenomenon analogous to Rydberg blockade at the level of molecules, opening the path toward studying many-body systems of ultralong-range Rydberg molecules.

Observation of photoassociation spectroscopy of 23Na spinor Bose-Einstein condensate

We report the high-resolution photoassociation (PA) spectroscopy of ²³Na excited from the spin-1 Bose-Einstein Condensate (BEC) to the molecular state of 0g-(P_3/2)v = 4 and 1_g(P_3/2)v = 91. By comparing the PA spectra of different spin configurations, we experimentally studied the effect of spin on the PA spectra. The experimental spectra comply well with the theoretical consideration. The results will play an important role in the study of the spin interaction and control of the antiferromagnetism in Na.

High sensitive trap loss spectroscopic detection of the lowest vibrational levels of ultracold molecules

We present a controllable three-dimensional fluorescence modulation technique for the high sensitive trap loss detection of ultracold molecules. The lowest vibrational levels (v = 0 and 1) of the pure long-range state 0(-)(g) (6S(1/2) + 6P(3/2)) of a cesium molecule are detected directly with high rotational resolution. Our technique proved to be a robust tool for effectively improving the detection sensitivity of trap loss spectroscopy.

Prospects for making polar molecules with microwave fields

We propose a mechanism to produce ultracold polar molecules with microwave fields. It converts trapped ultracold atoms into vibrationally excited molecules by a single microwave transition and entirely depends on the existence of a permanent dipole moment in the molecules. As opposed to production of molecules by photoassociation or magnetic-field Feshbach resonances, our method does not rely on properties of excited states or existence of Feshbach resonances. We determine conditions for optimal creation of polar molecules in vibrationally excited states of the ground-state potential by changing frequency and intensity of the microwave field. We also explore the possibility to produce vibrationally cold molecules by combining the microwave field with an optical Raman transition or by applying a microwave field to Feshbach molecules. The production mechanism is illustrated for KRb and RbCs.

Theoretical calculation of the low laying electronic states of the molecule NaCs with spin-orbit effect

The potential energy curves have been calculated for the 59 lowest electronic states of the molecule NaCs including the spin-orbit effect within the range of 4.5a(0)-20.0a(0) of the internuclear distance R. Using an ab initio method, the calculation is based on a nonempirical pseudopotentials which take into consideration the spin-orbit effect. Gaussian basis sets have been used for both atoms, and the spin-orbit effects have been taken into consideration. The spectroscopic constants have been calculated for 56 electronic states. The components of the spin-orbit splitting have been identified for the states (1,2,4)(3)Pi. The comparison of the present results with those available in the literature shows a very good agreement.

High-resolution photoassociation spectroscopy of ultracold ytterbium atoms by using the intercombination transition

We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0 - 3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested.

Theoretical calculation of the excited states of the KCs molecule including the spin-orbit interaction

For the molecule KCs the potential energy has been calculated for the 72 lowest molecular states Omega. Using an ab initio method the calculation is based on nonempirical pseudopotentials within the range of 5.0a0-34.0a0 of the internuclear distance R. Gaussian basis sets have been used for both atoms and spin-orbit effects have been taken into account through a semiempirical spin-orbit pseudopotential added to the electrostatic Hamiltonian. The spectroscopic constants for 60 states have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. The components of the spin-orbit splitting for (1,2,5,6) 3Pi and (1) 3delta have been identified. The comparison of the present results with those available in the literature shows a very good agreement, while the other results, to the best of our knowledge, are given here for the first time.

Parametric amplification of scattered atom pairs

We have observed parametric generation and amplification of ultracold atom pairs. A 87Rb Bose-Einstein condensate was loaded into a one-dimensional optical lattice with quasimomentum k0 and spontaneously scattered into two final states with quasimomenta k1 and k2 . Furthermore, when a seed of atoms was first created with quasimomentum k1 we observed parametric amplification of scattered atoms pairs in states k1 and k2 when the phase-matching condition was fulfilled. This process is analogous to optical parametric generation and amplification of photons and could be used to efficiently create entangled pairs of atoms. Furthermore, these results explain the dynamic instability of condensates in moving lattices observed in recent experiments.

Photoassociation spectroscopy of ultracold Cs below the 6P(3/2) limit

High precision photoassociation spectroscopy is performed in ultracold cesium gas, with detunings as large as 51 cm(-1) below the Cs(6S(1/2))+Cs(6P(3/2)) asymptote. Trap-loss fluorescence detection is used for detecting the photoassociation to excited state ultracold molecules. Long vibrational progressions are assigned to electronic states of 0(g) (-), 0(u) (+), and 1(g) symmetry. The spectral data are fitted to a LeRoy-Bernstein equation, in order to obtain the effective coefficients of the leading long-range interaction term (C(3)/R(3)) and the relative vibrational quantum numbers measured down from dissociation. Additionally we present evidence for perturbations between the 0(g) (-) state and the dark 2(u) state.

Photoassociation spectroscopy of laser-cooled ytterbium atoms

We report the photoassociation spectroscopy of laser-cooled ytterbium atoms in an optical trap. We observed more than 90 photoassociation resonances of vibrational levels in the (1)Sigma(+)(u) state, including 80 consecutive series, up to 490 GHz detuning with respect to the atomic resonance. From the resonance frequencies we derived the atomic radiative lifetime of the (6s6p) 1P1 state to be 5.464+/-0.005 ns, which is about 2 orders of magnitude improvement over previous results. We also observed line broadening of resonances, which is ascribed to the predissociation to the triplet states, and estimated the transition probability to be 0.2. Furthermore, we observed the decrease of the photoassociation signal intensity, from which the scattering length is estimated to be equal to or less than 3 nm.

State selective production of molecules in optical lattices

We demonstrate quantum control over both internal and external quantum degrees of freedom in a high number of identical "chemical reactions," carried out in an array of microtraps in a 3D optical lattice. Starting from a Mott insulating phase of an ultracold atomic quantum gas, we use two-photon Raman transitions to create molecules on lattice sites occupied by two atoms. In the atom-molecule conversion process, we can control both the internal rovibronic and external center of mass quantum state of the molecules. The lattice isolates the microscopic chemical reactions from each other, thereby allowing photoassociation spectra without collisional broadening even at high densities of up to 2 x 10(15) cm(-3).

Photoassociation spectroscopy of ultracold Cs below the 6P1/2 limit

We have performed high precision photoassociation spectroscopy of ultracold cesium gas. Using trap-loss fluorescence detection and controlling the background cesium pressure we were able to photoassociate atoms into excited states of ultracold molecules with large detunings up to 56 cm(-1) below the Cs(6S(1/2)) + Cs(6P(1/2)) atomic asymptote. Vibrational progressions are assigned to 0(g)(-), 0(u)(+), and 1(g) long-range states. By fitting the spectral data to the LeRoy-Bernstein expression, the effective coefficients of the leading long-range interactions and the vibrational quantum number at dissociation are obtained. In addition we have observed spectral perturbations between states of the same symmetry belonging to different asymptotes (6P(1/2) and 6P(3/2)). The perturbations are manifested through irregular vibrational level spacings and are especially pronounced in the 0(u)(+) symmetry. Many observed rotational levels indicate d- and higher partial wave contributions to the photoassociation cross section in the presence of trapping laser light, while spectral regions with only weak features suggest nodes in the lower state wave functions corresponding to the two ground state atoms asymptote.

Forbidden transitions in a magneto-optical trap

We report the first observation of a nondipole transition in an ultracold atomic vapor. We excite the 3P-4P electric quadrupole (E2) transition in 23Na confined in a magneto-optical trap, and we demonstrate its application to high-resolution spectroscopy by making the first measurement of the hyperfine structure of the 4P(1/2) level and extracting the magnetic dipole constant A=30.6+/-0.1 MHz. We use cw optical-optical double resonance accompanied by photoionization to probe the transition.

Photoassociation spectroscopy of cold He(2 3S) atoms

We observe vibrational states by photoassociation spectroscopy of cold He(2 3S) atoms. Photoassociation resonances are detected as peaks in the Penning ionization rate over a frequency range of 20 GHz below the atomic 2 3S1-2 3P2 transition frequency. We have observed three vibrational series, of which two can be identified. A possible mechanism to explain the observed increase of the Penning ionization rate is discussed.

Photoassociation of Ultracold Atoms: A New Spectroscopic Technique

The new spectroscopic technique of photoassociation of ultracold atoms is reviewed, with an emphasis on connecting this area to traditional bound-state molecular spectroscopy. In particular, in contrast to photoassociative spectra at thermal energies, which are broad and of low information content, photoassociative spectra of ultracold atoms are high resolution, permitting observation of small vibrational and rotational spacings of long-range molecular levels near dissociation (typically with outer classical turning points >20 Å). The types of detection and theoretical analysis employed are illustrated, primarily using the example of 39K2. Future directions and applications of this field (e.g., to ultracold molecular formation) are also discussed. Copyright 1999 Academic Press.

Photoassociative Spectroscopy and Formation of Cold Molecules in Cold Cesium Vapor: Trap-Loss Spectrum versus Ion Spectrum

We report on the experimental spectra of all the optically accessible long-range attractive molecular states of the Cs2 dimer below the 6s2S1/2 + 6p2P3/2 dissociation limit by molecular photoassociation of cold Cs atoms. The spectra are obtained by the usual trap-loss method as well as by pulsed-laser photoionization of Cs2 molecules into Cs+2 ions. The two spectra present markedly different features. While the 1g, 0(+)u, and 0(-)g vibrational progressions are present in the trap-loss spectrum, the Cs+2 ion spectrum presents only the 0(-)g and 1u vibrational progressions. Those states (0(-)g and 1u) lead to the formation of the translationally cold Cs2 ground state molecules at temperatures in the 100 µK range, to our knowledge the lowest molecular temperature reported up until now. The C3 asymptotic coefficients for the 0(+)u and 1g states are determined through a fit of the experimental energy levels. Copyright 1999 Academic Press.

Optical trapping and manipulation of neutral particles using lasers

The techniques of optical trapping and manipulation of neutral particles by lasers provide unique means to control the dynamics of small particles. These new experimental methods have played a revolutionary role in areas of the physical and biological sciences. This paper reviews the early developments in the field leading to the demonstration of cooling and trapping of neutral atoms in atomic physics and to the first use of optical tweezers traps in biology. Some further major achievements of these rapidly developing methods also are considered.

Dipole Polarizabilities of Li, C, and O and Long-Range Coefficients for Various Molecular States of Li2, CO, and O2

Dynamic polarizabilities with imaginary frequencies are calculated for Li(2s 2S), Li(3s 2S), Li(2p 2P), C(2p2 3P), and O(2p4 3P) atoms with a time-dependent gauge-invariant method. Coulombic long-range interactions are deduced for various states of Li2, CO, and O2 and compared to previous calculated and experimental results. Copyright 1997Academic Press