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arXiv:1811.03998 · Physical Review A

Formation of RbCs dimers using an elliptically polarized laser pulse

C. Chandré, J. Pablo Salas

Published Feb 1, 2019• 3 citations
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Abstract

We consider the formation of RbCs by an elliptically polarized laser pulse. By varying the ellipticity of the laser for sufficiently large laser intensity, we see that the formation probability presents a strong dependence, especially around ellipticity $1/\sqrt{2}$. We show that the analysis can be reduced to the investigation of the long-range interaction between the two atoms. The formation is mainly due to a small momentum shifts induced by the laser pulse. We analyze these results using the Silberstein expressions of the polarizabilities and show that the ellipticity of the field acts as a control knob for the formation probability, allowing significant variations of the dimer formation probability at a fixed laser intensity, especially in the region around an ellipticity of $1/\sqrt{2}$.

DOI
10.1103/physreva.99.023402

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We consider the formation of RbCs by an elliptically polarized laser pulse. By varying the ellipticity of the laser for sufficiently large laser intensity, we see that the formation probability presents a strong dependence, especially around ellipticity 1/21/\sqrt{2}1/2​. We show that the analysis can be reduced to the investigation of the long-range interaction between the two atoms. The formation is mainly due to a small momentum shifts induced by the laser pulse. We analyze these results using the Silberstein expressions of the polarizabilities and show that the ellipticity of the field acts as a control knob for the formation probability, allowing significant variations of the dimer formation probability at a fixed laser intensity, especially in the region around an ellipticity of 1/21/\sqrt{2}1/2​.
We study the formation of the RbCs molecule by an intense laser pulse using nonlinear dynamics. Under the Born-Oppenheimer approximation, the system is modeled by a two-degree-of-freedom rovibrational Hamiltonian, which includes the ground electronic potential energy curve of the diatomic molecule and the interaction of the molecular polarizability with the electric field of the laser. As the laser intensity increases, we observe that the formation probability first increases and then decreases after reaching a maximum. We show that the analysis can be simplified to the investigation of the long-range interaction between the two atoms. We conclude that the formation is due to a very small change in the radial momentum of the dimer induced by the laser pulse. From this observation, we build a reduced one-dimensional model which allows us to derive an approximate expression of the formation probability as a function of the laser intensity.
We determine conditions for effective quantum control over internal and external degrees of freedom of polar alkali-metal molecules in an optical trap. We calculate the dynamic molecular polarizability of KRb and RbCs as a function of laser frequency. The real part of the molecular polarizibility determines the depth of the trapping potential while the imaginary part contributes to laser-induced decoherences. Our results show that a relatively modest laser intensity is needed for strong confinement of polar molecules in an optical trap and that decoherence effects are manageable. More complete information on the scientific progress for the period of the extension is given in the Attachment.
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 85 Rb and 133 Cs atoms colliding on the X 1 Σ + 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 Ω=0 + levels in this region, which have mixed A 1 Σ + and b 3 Π character. We then study the quantum dynamics of RbCs by a time-dependent wavepacket (TDWP) approach. A wavepacket is formed by exciting a few vibronic levels and is allowed to propagate on the coupled electronic potential energy curves. We calculate the time dependence of the overlap between the wavepacket and ground-state vibrational levels. For a detuning of 7.5 cm −1 from the atomic line, the wavepacket for RbCs reaches the short-range region in about 13 ps, which is significantly faster than for the homonuclear Rb 2 system; this is mostly because of the absence of an R −3 long-range tail in the excited-state potential curves for heteronuclear systems. We give a simple semiclassical formula that relates the time taken to the long-range potential parameters. For RbCs, in contrast to Rb 2 , the excited-state wavepacket shows a substantial peak in singlet density near the inner turning point, and this produces a significant probability of de-excitation to form ground-state molecules bound by up to 1500 cm −1 . The short-range peak depends strongly on non-adiabatic coupling and is reduced if the strength of the spin–orbit coupling is increased. Our analysis of the role of spin–orbit coupling concerns the character of the mixed states in general and is important for both photoassociation and stimulated Raman de-excitation.
We have investigated photoassociative formation of RbCs molecules in the ${(2)}^{\phantom{\rule{0.16em}{0ex}}3}\phantom{\rule{-0.16em}{0ex}}\ensuremath{\Pi}$ excited state correlated to v=8v=8v=8, (5)0+(5){0}^{+}(5)0+ vibrational level in detail. The metastable ground-state RbCs molecules formed by spontaneous decay are ionized by pulsed dye laser through resonance-enhanced two-photon ionization. A rate equation of the photoionization process is introduced to explain the dependence of RbCs+{}^{+}+ molecular ion intensity on the ionization laser intensity. The saturation effect of molecular ion intensity appears as the photoassociation laser intensity increases. The rotational constant and centrifugal distortion constant are derived to be 0.01304 cm${}^{\ensuremath{-}1}$ and 0.000015 cm${}^{\ensuremath{-}1}$ from the photoassociation spectrum with a high sensitivity, respectively. The measured electric dipole moment of the observed $(2){\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}\ensuremath{\Pi}$ state RbCs molecules is 4.7(6) D by Stark effect in static electric field.
The paper investigates cold molecules formation in the photoassociation of two cold atoms by a strong laser pulse applied at short interatomic distances, which lead to a molecular dynamics taking place in the light-induced (adiabatic) potentials. A two electronic states model in the cesium dimer is used to analyse the effects of this strong coupling regime and to show specific results: i) acceleration of the ground state population to the inner zone due to a non-impulsive regime of coupling at short and intermediate interatomic distances; ii) formation of cold molecules in strongly bound levels of the ground state, where the population at the end of the pulse is much bigger than the population photoassociated in bound levels of the excited state; iii) the final momentum distribution of the ground state wavepacket keeping the signatures of the maxima in the initial wavefunction continuum. It is shown that the topology of the light-induced potentials plays an important role in dynamics.
This paper investigates the formation of cold molecules in the photoassociation of two cold atoms by a strong laser pulse applied at short interatomic distances, which lead to molecular dynamics taking place in the light-induced (adiabatic) potentials. A two-electronic-state model in the caesium dimer is used to analyse the effects of this strong coupling regime and to show specific results: (i) acceleration of the ground-state population to the inner zone due to a non-impulsive regime of coupling at short and intermediate interatomic distances, (ii) formation of cold molecules in strongly bound levels of the ground state, where the population at the end of the pulse is much bigger than the population photoassociated in bound levels of the excited state, and (iii) the final momentum distribution of the ground-state wavepacket keeping the signatures of the maxima in the initial wavefunction continuum. It is shown that the topology of the light-induced potentials plays an important role in dynamics.