Creation of a low-entropy quantum gas of polar molecules in an optical lattice

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Science  06 Nov 2015:
Vol. 350, Issue 6261, pp. 659-662
DOI: 10.1126/science.aac6400

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Filling a molecular lattice of light

Cold atoms in optical lattices normally interact only when two of them occupy the same lattice site. More-complex interactions would expand the potential of the system for quantum simulation. A promising approach is to use polar molecules instead of atoms, which interact at much longer length scales. However, “packing” the lattice with molecules is tricky. Moses et al. introduced bosonic 87Rb atoms and fermionic 40K atoms into an optical lattice, combined them into molecules, and brought the molecules into their ground state, achieving a considerable lattice filling of 25%.

Science, this issue p. 659


Ultracold polar molecules, with their long-range electric dipolar interactions, offer a unique platform for studying correlated quantum many-body phenomena. However, realizing a highly degenerate quantum gas of molecules with a low entropy per particle is challenging. We report the synthesis of a low-entropy quantum gas of potassium-rubidium molecules (KRb) in a three-dimensional optical lattice. We simultaneously load into the optical lattice a Mott insulator of bosonic Rb atoms and a single-band insulator of fermionic K atoms. Then, using magnetoassociation and optical state transfer, we efficiently produce ground-state molecules in the lattice at those sites that contain one Rb and one K atom. The achieved filling fraction of 25% should enable future studies of transport and entanglement propagation in a many-body system with long-range dipolar interactions.

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