This theoretical paper presents numerical calculations for photoassociation of ultracold cesium atoms with a chirped laser pulse and detailed analysis of the results. In contrast with earlier work, the initial state is represented by a stationary continuum wavefunction. In the chosen example, it is shown that an important population transfer is achieved to ≈ 15 vibrational levels in the vicinity of the v=98 bound level in the external well of the 0 − g (6s + 6p 3/2 ) potential. Such levels lie in the energy range swept by the instantaneous frequency of the pulse, thus defining a "photoassociation window". Levels outside this window may be significantly excited during the pulse, but no population remains there after the pulse. Finally, the population transfer to the last vibrational levels of the ground a 3 Σ + u (6s + 6s) is significant, making stable molecules. The results are interpreted in the framework of a two state model as an adiabatic inversion mechanism, efficient only within the photoassociation window. The large value found for the photoassociation rate suggests promising applications. The present chirp has been designed in view of creating a vibrational wavepacket in the excited state which is focussing at the barrier of the double well potential.

Abstract. Photoassociation of ultracold atoms induced by chirped picosecond pulses is analyzed in a nonperturbative treatment by following the wavepackets dynamics on the ground and excited surfaces. The initial state is described by a Boltzmann distribution of continuum scattering states. The chosen example is photoassociation of cesium atoms at temperature T=54 µK from the a 3 Σ + u (6s, 6s) continuum to bound levels in the external well of the 0 − g (6s + 6p 3/2 ) potential. We study how the modification of the pulse characteristics (carrier frequency, duration, linear chirp rate and intensity) can enhance the number of photoassociated molecules and suggest ways of optimizing the production of stable molecules.

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We investigate the entanglement between electronic and vibrational degrees of freedom produced by a vibronic coupling in a molecular system described in the Born-Oppenheimer approximation.Entanglement in a pure state of the Hilbert space H=H el H vib is quantified using the von Neumann entropy of the reduced density matrix and the reduced linear entropy. Expressions for these entanglement measures are derived for the 2 × N v and 3 × N v cases of the bipartite entanglement, where 2 and 3 are the dimensions of the electronic Hilbert space H el , and N v is the dimension of H vib . We study the entanglement dynamics for two electronic states coupled by a laser pulse (a 2 × N v case), taking as an example a coupling between the a 3 Σ + u (6s, 6s) and 1 g (6s, 6p 3/2 ) states of the Cs 2 molecule. The reduced linear entropy expression obtained for the 3 × N v case is used to follow the entanglement evolution in a scheme proposed for the control of the vibronic dynamics in a Cs 2 cold molecule, implying the a 3 Σ + u (6s, 6s), 0 − g (6s, 6p 3/2 ), and 0 − g (6s, 5d) electronic states, which are coupled by a non-adiabatic radial coupling and a sequence of chirped laser pulses.

Abstract. We calculate the rates of formation and detection of ultracold Cs 2 molecules obtained from the photoassociation of ultracold atoms through the doublewell 0

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