Controlled Formation of Ultracold NaCs Molecules by Photoassociation via Adiabatic Passage

High resolution photoassociation spectroscopy of the excited $c^3Σ_{1}^+$ potential of $^{23}$Na$^{133}$Cs

We report on photoassociation spectroscopy probing the $c^3Σ_{1}^+$ potential of the bi-alkali NaCs molecule, identifying eleven vibrational lines between $v' = 0$ and $v' = 25$ of the excited $c^3Σ_{1}^+$ potential, and resolving their rotational and hyperfine structure. The observed lines are assigned by fitting to an effective Hamiltonian model of the excited state structure with rotational and hyperfine constants as free parameters. We discuss unexpected broadening of select vibrational lines, and its possible link to strong spin-orbit coupling of the $c^3Σ_{1}^+$ potential with the nearby…

Photoassociation of ultracold LiRb* molecules: observation of high efficiency and unitarity-limited rate saturation

We report the production of ultracold heteronuclear 7Li85Rb molecules in excited electronic states by photoassociation (PA) of ultracold 7Li and 85Rb atoms. PA is performed in a dual-species 7Li-85Rb magneto-optical trap (MOT) and the PA resonances are detected using trap loss spectroscopy. We identify several strong PA resonances below the Li (2s 2S1/2) + Rb (5p 2P3/2) asymptote and experimentally determine the long range C6 dispersion coefficients. We find a molecule formation rate (P_LiRb) of 3.5x10^7 s^-1 and a PA rate coefficient (K_PA) of 1.3x10^-10 cm^3/s, the highest among heteronuclea…

Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses - I. Experiment

We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D1 or D2 asymptote. Time-resolved pump-probe spectra reveal coherent oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detun-ing of the sp…

Two-photon photoassociation spectroscopy of an ultracold heteronuclear molecule

We report on two-photon photoassociation (PA) spectroscopy of ultracold heteronuclear LiRb molecules. This is used to determine the binding energies of the loosely bound levels of the electronic ground singlet and the lowest triplet states of LiRb. We observe strong two-photon PA lines with power broadened line widths greater than 20 GHz at relatively low laser intensity of 30 W/cm$^{2}$. The implication of this observation on direct atom to molecule conversion using stimulated Raman adiabatic passage (STIRAP) is discussed and the prospect for electronic ground state molecule production is the…

Formation of ultracold LiRb molecules by photoassociation near the Li (2s 2S1/2) + Rb (5p 2P1/2) asymptote

We report the production of ultracold 7Li85Rb molecules by photoassociation (PA) below the Li (2s 2S1/2) + Rb (5p 2P1/2) asymptote. We perform PA spectroscopy in a dual-species 7Li-85Rb magneto-optical trap (MOT) and detect the PA resonances using trap loss spectroscopy. We observe several strong PA resonances corresponding to the last few bound states, assign the lines and derive the long range C6 dispersion coefficients for the Li (2s 2S1/2) + Rb (5p 2P1/2) asymptote. We also report an excited-state molecule formation rate (P_LiRb) of ~10^7 s^-1 and a PA rate coefficient (K_PA) of ~4x10^-11 …

A pump-probe study of the formation of rubidium molecules by ultrafast photoassociation of ultracold atoms

An experimental pump-probe study of the photoassociative creation of translationally ultracold rubidium molecules is presented together with numerical simulations of the process. The formation of loosely bound excited-state dimers is observed as a first step towards a fully coherent pump-dump approach to the stabilization of Rb$_2$ into its lowest ground vibrational states. The population that contributes to the pump-probe process is characterized and found to be distinct from a background population of pre-associated molecules.

Towards photoassociation processes of ultracold rubidium trimers

We theoretically investigate the prospects for photoassociation (PA) of Rb$_3$, in particular at close range. We provide an overview of accessible states and possible transitions. The major focus is placed on the calculation of equilibrium structures, the survey of spin-orbit effects and the investigation of transition dipole moments. Furthermore we discuss Franck-Condon overlaps and special aspects of trimers including the (pseudo) Jahn-Teller effect and the resulting topology of adiabatic potential-energy surfaces. With this we identify concrete and suitable PA transitions to potentially pro…

Modeling photoassociative spectra of ultracold NaK+K

A model for photoassociation of ultracold atoms and molecules is presented, and applied to the case of $^{39}$K and $^{23}$Na$^{39}$K bosonic particles. The model relies on the assumption that photoaossociation 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 $X^1Σ^+$ ground state toward the metastable $b^3Π$ lowest excited state of $^{23}$Na$^{39}$K, allowing to neglect any other excitation which could hinder the photoassociation detection. T…

三原子光关联在超冷原子-分子碰撞中的研究

Triatomic Photoassociation in an Ultracold Atom-Molecule Collision

本研究通过理论分析，探讨了超冷条件下碱土原子与双原子分子碰撞中光子吸收的三原子复合物形成机制，并验证了模型与已有实验结果的一致性。

Formation of deeply bound ultracold LiRb molecules via photoassociation near the Li 2S$_{1/2}$ + Rb 5P$_{3/2}$ asymptote

We present spectra of ultracold $^7$Li$^{85}$Rb molecules in their electronic ground state formed by spontaneous decay of weakly bound photoassociated molecules. Beginning with atoms in a dual species magneto-optical trap (MOT), weakly bound molecules are formed in the 4(1) electronic state, which corresponds to the B$^1Π$ state at short range. These molecules spontaneously decay to the electronic ground state and we use resonantly enhanced multiphoton ionization (REMPI) to determine the vibrational population distribution in the electronic ground states after spontaneous emission. Many of the…

Molecule formation in ultracold atomic gases

This review describes recent experimental and theoretical advances in forming molecules in ultracold gases of trapped alkali metal atoms, both by magnetic tuning through Feshbach resonances and by photoassociation. Molecular Bose-Einstein condensation of long-range states of both boson dimers and fermion dimers was achieved in 2002-3. Condensates of boson dimers were found to be short-lived, but long-lived condensates of fermion dimers have been produced. Signatures of triatomic and tetraatomic molecules have recently been observed. Both homonuclear and heteronuclear molecules have been formed…

超冷极性分子间的取向输运

Alignment Transport Between Ultracold Polar Molecules

本文提出利用超冷极性分子阵列研究分子间取向输运，揭示了电场驱动激发与偶极-偶极相互作用的协同机制，并以NaCs为例证明取向转移时间约为10微秒，具备实验可观测性。

Chemical Oscillation in Ultracold Chemistry

We demonstrate the occurrence of oscillatory reactions in the ultra-cold chemistry of atom-molecular Bose-Einstein condensate. Nonlinear oscillations in the mean-field dynamics occur for a specific range of elliptic modulus, giving rise to both in- and out-phase modulations in the atom-molecule population density. The reaction front velocity is found to be controlled by photoassociation, which also regulates the condensate density. Two distinct pair of in-phase bright localized gap solitons are found as exact solutions, existence of one of which necessarily requires a background. Cnoidal atomi…

Optimized production of ultracold ground-state molecules: Stabilization employing potentials with ion-pair character and strong spin-orbit coupling

We discuss the production of ultracold molecules in their electronic ground state by photoassociation employing electronically excited states with ion-pair character and strong spin-orbit interaction. A short photoassociation laser pulse drives a non-resonant three-photon transition for alkali atoms colliding in their lowest triplet state. The excited state wave packet is transferred to the ground electronic state by a second laser pulse, driving a resonant two-photon transition. After analyzing the transition matrix elements governing the stabilization step, we discuss the efficiency of popul…

Optical Production of Ultracold Polar Molecules

We demonstrate the production of ultracold polar RbCs molecules in their vibronic ground state, via photoassociation of laser-cooled atoms followed by a laser-stimulated state transfer process. The resulting sample of $X ^1Σ^+ (v=0)$ molecules has a translational temperature of $\sim100 μ$K and a narrow distribution of rotational states. With the method described here it should be possible to produce samples even colder in all degrees of freedom, as well as other bi-alkali species.

Perspectives for coherent optical formation of strontium molecules in their electronic ground state

Optical Feshbach resonances [Phys. Rev. Lett. 94, 193001 (2005)] and pump-dump photoassociation with short laser pulses [Phys. Rev. A 73, 033408 (2006)] have been proposed as means to coherently form stable ultracold alkali dimer molecules. In an optical Feshbach resonance, the intensity and possibly frequency of a cw laser are ramped up linearly followed by a sudden switch-off of the laser. This is applicable to tightly trapped atom pairs. In short-pulse photoassociation, the pump pulse forms a wave-packet in an electronically excited state. The ensuing dynamics carry the wave-packet to short…

Production and state-selective detection of ultracold, ground state RbCs molecules

Using resonance-enhanced two-photon ionization, we detect ultracold, ground-state RbCs molecules formed via photoassociation in a laser-cooled mixture of 85Rb and 133Cs atoms. We obtain extensive bound-bound excitation spectra of these molecules, which provide detailed information about their vibrational distribution, as well as spectroscopic data on the RbCs ground a^3Σ^+ and excited (2)^3Σ^+, (1)^1Πstates. Analysis of this data allows us to predict strong transitions from observed excited levels to the absolute vibronic ground state of RbCs, potentially allowing the production of stable, ult…

光学激发与稳定超冷电场耦合四聚体分子

Optical excitation and stabilization of ultracold field-linked tetratomic molecules

通过受激拉曼绝热传递和光结合技术，研究电场耦合四聚体分子在超冷条件下的激发与稳定，为多原子分子的深度束缚提供新方法。

偶极阱中多种冷分子的光缔合

Photoassociation of multiple cold molecules in a dipole trap

本文通过在磁光阱中对Rb2进行光缔合获得精确振转光谱，并首次在光学偶极阱中实现多种振转态冷分子的光缔合，为同时制备不同种类冷分子及碰撞动力学研究提供了通用方法。

Cavity-controlled ultracold chemistry

Ultracold ground-state molecules can be formed from ultracold atoms via photoassociation followed by a spontaneous emission process. Typically, the molecular products are distributed over a range of final states. Here, we propose to use an optical cavity with high cooperativity to selectively enhance the population of a pre-determined final state by controlling the spontaneous emission. During this process, a photon will be emitted into the cavity mode. Detection of this photon heralds a single reaction. We discuss the efficiency and the dynamics of cavity-assisted molecule formation in the fr…

Engineering an all-optical route to ultracold molecules in their vibronic ground state

We propose an improved photoassociation scheme to produce ultracold molecules in their vibronic ground state for the generic case where non-adiabatic effects facilitating transfer to deeply bound levels are absent. Formation of molecules is achieved by short laser pulses in a Raman-like pump-dump process where an additional near-infrared laser field couples the excited state to an auxiliary state. The coupling due to the additional field effectively changes the shape of the excited state potential and allows for efficient population transfer to low-lying vibrational levels of the electronic gr…

Cold interactions between an Yb$^+$ ion and a Li atom: Prospects for sympathetic cooling, radiative association, and Feshbach resonances

The electronic structure of the (LiYb)$^+$ molecular ion is investigated with two variants of the coupled cluster method restricted to single, double, and noniterative or linear triple excitations. Potential energy curves for the ground and excited states, permanent and transition electric dipole movements, and long-range interaction coefficients $C_4$ and $C_6$ are reported. The data is subsequently employed in scattering calculations and photoassociation studies. Feshbach resonances are shown to be measurable despite the ion's micromotion in the Paul trap. Molecular ions can be formed in the…

Stimulating the production of deeply bound RbCs molecules with laser pulses: the role of spin-orbit coupling in forming ultracold molecules

We investigate the possibility of forming deeply bound ultracold RbCs molecules by a two-color photoassociation experiment. We compare the results with those for Rb_2 in order to understand the characteristic differences between heteronuclear and homonuclear molecules. The major differences arise from the different long-range potential for excited states. Ultracold 85Rb and 133Cs atoms colliding on the X^1Sigma+ potential curve are initially photoassociated to form excited RbCs molecules in the region below the Rb(5S) + Cs(6P_1/2) asymptote. We explore the nature of the Omega=0^+ levels in thi…

Experimental investigation of ultracold atom-molecule collisions

Ultracold collisions between Cs atoms and Cs2 dimers in the electronic ground state are observed in an optically trapped gas of atoms and molecules. The Cs2 molecules are formed in the triplet ground state by cw-photoassociation through the outer well of the 0g-(P3/2) excited electronic state. Inelastic atom-molecule collisions converting internal excitation into kinetic energy lead to a loss of Cs2 molecules from the dipole trap. Rate coefficients are determined for collisions involving Cs atoms in either the F=3 or F=4 hyperfine ground state and Cs2 molecules in either highly vibrationally e…

Ultracold Molecule Assembly with Photonic Crystals

Photoassociation (PA) is a powerful technique to synthesize molecules directly and continuously from cold and ultracold atoms into deeply bound molecular states. In freespace, however, PA efficiency is constrained by the number of spontaneous decay channels linking the initial excited molecular state to a sea of final (meta)stable rovibronic levels. Here, we propose a novel scheme based on molecules strongly coupled to a guided photonic mode in a photonic crystal waveguide that turns PA into a powerful tool for near deterministic formation of ultracold molecules in their ground rovibrational l…

原子和双原子分子的结构与相互作用：从超冷气体到掺杂固体

Structure and interactions of atoms and diatomic molecules: from ultracold gases to doped solids

本文综述了博士后研究，第一部分涉及中性三价镧系元素的原子结构计算，应用于超冷气体和稀土掺杂固体；第二部分研究碱金属原子、双原子分子及镧系原子的长程相互作用，用于表征超低温现象如光缔合和碰撞屏蔽。

利用光学方法形成超冷NaK₂基态分子

Optical formation of ultracold NaK$_2$ ground state molecules

通过计算NaK₂分子的转动能跃迁，研究利用光学方法生成超冷基态三原子分子的可行性。

Ultracold $^{88}\rm{Sr}_2$ molecules in the absolute ground state

We report efficient all-optical creation of an ultracold gas of alkaline-earth-metal dimers, $^{88}\rm{Sr}_2$, in their absolute ground state. Starting with weakly bound singlet molecules formed by narrow-line photoassociation in an optical lattice, followed by stimulated Raman adiabatic passage (STIRAP) via a singlet-dominant channel in the $(1)0_u^+$ excited potential, we prepare pure samples of more than 5500 molecules in $X^1Σ_g^+(v=0,J=0)$. We observe two-body collisional loss rates close to the universal limit for both the least bound and most bound vibrational states in $X^1Σ_g^+$. We d…

Laser cooling of a diatomic molecule

It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in a vast array of fields. Unfortunately laser cooling has not yet been extended to molecules because of their complex internal structure. However, this complexity makes molecules potentially useful for many applications. For example, heteronuclear molecules possess permanent electric dipole moments which lead to long-range, tunable, anisotropic dipole-dipole interactions. The combination of the dipole-dipole interaction and the precise control over molecular degrees of freedom …

Bose-Einstein Condensate of Trimers Dressed by Atom-Dimer Cooper Pairs

We theoretically examine the neutral atom-molecule analogue of the anomalous quantum correlations between degenerate electrons, i.e., Cooper pairs, that are responsible for superconductivity. Based on rogue dissociation of triatomic molecules (trimers) into opposite-momentum pairs of atoms and diatomic molecules (dimers) via a photoassociation or Feshbach resonance, we find a superfluid transition to a Bose-Einstein condensate of trimers dressed by atom-dimer Cooper pairs, at a critical temperature in reach of present ultracold technology.

Ab initio electronic structure and prospects for the formation of ultracold calcium--alkali-metal-atom molecular ions

Experiments with cold ion-atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an alkali-metal atom: CaAlk$^{+}$ (Alk=Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotential, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potentia…

New Directions in Degenerate Dipolar Molecules via Collective Association

We survey results on the creation of heteronuclear Fermi molecules by tuning a degenerate Bose-Fermi mixture into the neighborhood of an association resonance, either photoassociation or Feshbach, as well as the subsequent prospects for Cooper-like pairing between atoms and molecules. In the simplest case of only one molecular state, corresponding to either a Feshbach resonance or one-color photoassociation, the system displays Rabi oscillations and rapid adiabatic passage between a Bose-Fermi mixture of atoms and fermionic molecules. For two-color photoassociation, the system admits stimulate…

The RbSr $^2Σ^+$ ground state investigated via spectroscopy of hot & ultracold molecules

We report on spectroscopic studies of hot and ultracold RbSr molecules, and combine the results in an analysis that allows us to fit a potential energy curve (PEC) for the X(1)$^2Σ^+$ ground state bridging the short-to-long-range domains. The ultracold RbSr molecules are created in a $μ$K sample of Rb and Sr atoms and probed by two-colour photoassociation spectroscopy. The data yield the long-range dispersion coefficients $C_6$ and $C_8$, along with the total number of supported bound levels. The hot RbSr molecules are created in a $1000 \,$K gas mixture of Rb and Sr in a heat-pipe oven and pr…

Rydberg molecule-induced remote spin-flips

We have performed high resolution photoassociation spectroscopy of rubidium ultra long-range Rydberg molecules in the vicinity of the 25$P$ state. Due to the hyperfine interaction in the ground state perturber atom, the emerging mixed singlet-triplet potentials contain contributions from both hyperfine states. We show that this can be used to induce remote spin-flips in the perturber atom upon excitation of a Rydberg molecule. When furthermore the spin-orbit splitting of the Rydberg state is comparable to the hyperfine splitting in the ground state, the orbital angular momentum of the Rydberg …