Molecule formation in ultracold atomic gases

Abstract

This review describes recent experimental and theoretical advances in forming molecules in ultracold gases of trapped alkali metal atoms, both by magnetic tuning through Feshbach resonances and by photoassociation. Molecular Bose–Einstein condensation of long-range states of both boson dimers and fermion dimers was achieved in 2002–2003. Condensates of boson dimers were found to be short-lived, but long-lived condensates of fermion dimers have been produced. Signatures of triatomic and tetraatomic molecules have recently been observed. Both homonuclear and heteronuclear molecules have been formed by photoassociation, mostly in very high vibrational levels. Recent attempts to produce ultracold molecules in short-range states (low vibrational levels) are described. Experimental and theoretical work on collisions of ultracold molecules is discussed. 1. Introduction 498 2. Basic properties of ultracold atomic gases 499 2.1. Bosons and fermions 499 2.2. Hyperfine structure 499 2.3. Trapping and cooling 500 2.4. Bose–Einstein condensation and Fermi degeneracy 501 2.5. Scattering lengths 502 2.6. Feshbach resonances 503 3. Molecules formed by Feshbach resonance tuning 506 3.1. Dimers of bosonic atoms 506 3.2. Dimers of fermionic atoms 508 3.3. Heteronuclear Feshbach resonances 511 3.4. Triatomic and larger molecules 512 4. Molecules formed by photoassociation 512 4.1. Photoassociation in Bose–Einstein Condensates 514 4.2. Coherent control 515 4.3. Molecules in low vibrational states 516 5. Molecules in optical lattices 517 6. Collisions of ultracold molecules 519 7. Conclusions 521 Acknowledgments 522 References 522