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arXiv:1511.00168 · Physical Review A

Photoassociative cooling and trapping of a pair of interacting atoms

Subrata Saha, Somnath Naskar, Bimalendu Deb

Published Aug 19, 2016• 2 citations
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Abstract

We show that it is possible to cool interacting pairs of atoms by a lin $\ensuremath{\perp}$ lin Sisyphus-like laser cooling scheme using counterpropagating photoassociation (PA) lasers. It is shown that the center-of-mass (c.m.) motion of atom pairs can be trapped in molecular spin-dependent periodic potentials generated by the lasers. The proposed scheme is most effective for narrow-line PA transitions. We illustrate this with numerical calculations using fermionic $^{171}\mathrm{Yb}$ atoms as an example.

DOI
10.1103/physreva.94.023413

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We show that it is possible to cool interacting pairs of atoms by a lin \ensuremath⊥\ensuremath{\perp}\ensuremath⊥ lin Sisyphus-like laser cooling scheme using counterpropagating photoassociation (PA) lasers. It is shown that the center-of-mass (c.m.) motion of atom pairs can be trapped in molecular spin-dependent periodic potentials generated by the lasers. The proposed scheme is most effective for narrow-line PA transitions. We illustrate this with numerical calculations using fermionic 171Yb^{171}\mathrm{Yb}171Yb atoms as an example.
In a recent paper, we have proposed a novel laser cooling scheme for reducing collisional energy of a pair of atoms by using photoassociative transitions. In that paper, we considered two atoms in free space, that is we have not considered the effects of trap on the cooling process. Here in this paper, we qualitatively discuss the possibility of extending this idea for Raman sideband cooling of a pair of interacting atoms trapped in Lamb-Dicke (LD) regime. Apart from cooling, our method may be important for manipulating on-site interaction of atoms in an optical lattice.
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The analysis of atomic motion in the field formed by sequences of counterpropagating light pulses reveals the conditions when the field creates the trap in which the temperature of trapped atoms drops to the Doppler limit. The atomic state is described by the wave function using the Monte Carlo wave function method, whereas the atomic motion is considered in the framework of classical mechanics. Laser cooling and trapping is achieved only for non-resonant atom–field interaction. The pulse area does not matter for this effect, in contrast to the repetition period. When the motion of a trapped atom is slowed down, it oscillates around the anti-nodes of a non-stationary standing wave formed by the counterpropagating light pulses at the point where they ‘collide’. The discussed trap is also applicable for trapping and cooling of the molecules for which the matrix of Frank–Condon factors is almost diagonal.
We discuss a possible one-dimensional trapping and cooling of atoms and molecules due to their nonresonant interaction with counterpropagating light pulse trains. The counterpropagating pulses form a one-dimensional trap for atoms and molecules and a properly chosen carrier frequency detuning from the transition frequency of the atoms or molecules keeps the temperature of the atomic or molecular ensemble close to the Doppler cooling limit. The calculation by the Monte Carlo wave-function method is carried out for the two-level and three-level schemes of the atom's and the molecule's interaction with the field, respectively. The models discussed are applicable to atoms and molecules with almost diagonal Frank-Condon factor arrays. Illustrative calculations are carried out for ensemble-averaged characteristics for sodium atoms and SrF molecules in the trap. The potential for the nanoparticle light pulses's trap formed by counterpropagating light pulse trains is also discussed.
Laser cooling of single atoms in optical tweezers is a prerequisite for neutral atom quantum computing and simulation. Resolved sideband cooling comprises a well-established method for efficient motional ground-state preparation, but typically requires careful cancellation of light shifts in so-called magic traps. Here, we study a novel laser cooling scheme which overcomes such constraints, and applies when the ground state of a narrow cooling transition is trapped stronger than the excited state. We demonstrate our scheme, which exploits sequential addressing of red sideband transitions via frequency chirping of the cooling light, at the example of 88Sr^{88}\mathrm{Sr}88Sr atoms and report ground-state populations compatible with recent experiments in magic tweezers. The scheme also induces light-assisted collisions, which are key to the assembly of large atom arrays. Our work enriches the toolbox for tweezer-based quantum technology, also enabling applications for tweezer-trapped molecules and ions that are incompatible with resolved sideband cooling conditions.