Abstract
Some of us have recently reported (Viteau et al 2008 Science 321 232–4) vibrational cooling of translationally cold Cs2 molecules into the lowest vibrational level v=0 of the singlet X1Σg ground electronic state. Starting from a sample of cold molecules produced in a collection of vibrational levels of the ground state, our method was based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but frequency-limited in such a way to eliminate transitions from v=0 level, in which molecules accumulate. In this paper, this method is generalized to accumulate molecules into an arbitrary selected ‘target’ vibrational level. It is implemented by using ultrashort pulse shaping techniques based on liquid crystal spatial light modulator. In particular, a large fraction of the initially present molecules is transferred into a selected vibrational level such as v=1, 2 and 7. Limitations of the method as well as the possible extension to rotational cooling are also discussed.
Highlights
The manipulation of atomic or molecular quantum dynamics and the availability of robust and selective methods of executing population transfer in quantum systems is essential for a variety of fields
The important activities developed in the cold molecule domain through precise control of both internal and external degrees of freedom of a molecule is expected to lead to significant advances in collision dynamics of chemical reactions, molecular spectroscopy, molecular clocks, fundamental test in physics, controlled photo-chemistry studies, and in quantum computation with the use of polar molecules [6, 7, 8, 9, 10, 11]
As in the work presented in Ref. [1], the cold molecule formation is achieved in a Cs vapor-loaded Magneto-Optical Trap (MOT) via photoassociation where two atoms resonantly absorb a photon to create a molecule in an excited electronic state which decay into stable deeply bound vibrational levels of the singlet molecular ground X state
Summary
The manipulation of atomic or molecular quantum dynamics and the availability of robust and selective methods of executing population transfer in quantum systems is essential for a variety of fields. During the last two decades many results including coherent control [19, 20, 21], compression of optical pulses [22] and optical communications [23] have been obtained by the use of arbitrarily shaped optical waveforms Most of these works were spurred by technological breakthroughs. The most usual device for both high fidelity and wide flexibility of shapes involves a pair of diffraction gratings and lenses arranged in a zero-dispersion line [25] with a pulse shaping mask at the Fourier plane In this paper this technique will be used to improve the vibrational cooling of molecules using amplitude shaping only. Using the flexibility of femtosecond pulse shaping techniques [24], this incoherent population pumping method is extended in order to accumulate molecules into other single selected vibrational level than the sole v = 0 one. Perspectives for very large band vibrational cooling and for rotational cooling are briefly theoretically addressed
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