1. World of zero temperature --- introduction to systems of ultracold atoms National Tsing-Hua University Daw-Wei Wang

2. Temperature ? What we mean by “ultracold” ?

3. Why low temperature ? Ans: To see the quantum effects ! Uncertainty principle:

4. (after Nature, 416, 225 (’02))

5. How to reach ultracold temperature ? Normal pressure: He 4  4.2 K We need very low density to avoid strong binding, i.e. we need low “kinetic energy”, not low “potential energy” !

6. How to reach ultracold temperature ? 1. Laser cooling ! (1997 Nobel Price) Use red detune laser + Doppler effect

7. How to reach ultracold temperature ? 2. Evaporative cooling ! Reduce potential barrial +thermal equilibrium

8. Typical experimental environment MIT

9. How to do measurement ? Trapping and cooling Perturbing Releasing and measuring BEC (2001 Nobel Price)

10. What is Bose-Einstein condensation ? Therefore, when T-> 0, noninteracting bosons like to stay in the lowest energy state, i.e. BEC

11. How about fermions in T=0 ? Therefore, when T-> 0, noninteracting fermions form a compact distribution in energy level. E D(E) Fermi sea

12. BEC and Superfluidity of bosons Superfluid Normal fluid v repulsion Landau’s two-fluid model BEC = superfluidity uncondensate condensate (after Science, 293, 843 (’01))

13. Phonons and interference in BEC Phonon=density fluctuation Interference Matter waves ? (after Science 275, 637 (’97))

14. Vortices in condensate Vortex = topological disorder E L 1320 Vortices melting, quantum Hall regime ? (after Science 292, 476 (’01)) (after PRL 87, 190401 (’01))

15. Spinor condensation in optical trap Na B E F=2 F=1 (see for example, cond-mat/0005001)

16. Boson-fermion mixtures Sympathetic cooling collapse E D(E) Interacting fermi sea Fermions are noninteracting ! rf-pulse phonon-mediated interaction fermion phonon (after Science 291, 2570 (’01)) (after Nature 412, 295 (’01))

17. Feshbach Resonance (i) Typical scattering: (ii) Resonant scattering: B a

18. Molecule and pair condensate (JILA, after Nature 424, 47 (’03)) (MIT group, PRL 92, 120403 (’04)) (Innsbruck, after Science 305, 1128 (’04))

19. Optical lattice 3D lattice 1D lattice Entanglement control other lattice

20. Mott-Insulator transition (after Nature 415, 39 (’02)) n=1 n=2 n=3 superfluid

21. Atom laser Bragg scattering Continuous source for coherent atoms

22. Transport in 1D waveguide Interference ? Finite temperature + semiconductor technique wave guide wire

23. Interdisciplinary field Ultracold atoms Traditional AMO Quantum Information Nonlinear Physics Precise measurement Condensed matter