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Martin Zwierlein

TOPS, MIT, Cambridge, June 24 th , 2009. Pairs and Loners in Ultracold Fermi Gases. Martin Zwierlein. Massachusetts Institute of Technology Center for Ultracold Atoms at MIT and Harvard $$$: NSF, AFOSR- MURI, Sloan Foundation. Bosons vs Fermions. E F. Bosons. Fermions.

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Martin Zwierlein

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  1. TOPS, MIT, Cambridge, June 24th, 2009 Pairs and Loners inUltracold Fermi Gases Martin Zwierlein Massachusetts Institute of Technology Center for Ultracold Atoms at MIT and Harvard $$$: NSF, AFOSR- MURI, Sloan Foundation

  2. Bosons vs Fermions EF Bosons Fermions e.g.: e-, 3He, 6Li, 40K e.g.: 1H, 23Na, 6Li2

  3. Degenerate gases de Broglie wavelength ~ Interparticle spacing Want lifetime > 1s Ultradilute Ultracold Good news: Bosons condense at

  4. Effusive beam Effusive atomic beam Gas How to measure temperature?

  5. Effusive beam Effusive atomic beam Gas How to measure temperature?

  6. Observation of the atom cloud Trapped Expanded Lens Atom cloud CCDCamera Laser beam Shadow imageof the cloud 1 mm

  7. BEC phase transition BEC @ MIT, 1995 (Sodium)

  8. Superfluidity in Bosonic Gases BEC @ JILA, Juni ‘95(Rubidium) BEC @ MIT, Sept. ‘95 (Sodium) ENS • Superfluidity 1999/2000Frictionless flow,quantized vorticity MIT JILA • BEC 1995All atoms occupy samemacroscopic wavefunction MIT • Phase coherence 1997

  9. Fermions – The Building Blocks of Matter Lithium-6 Harvard-Smithsonian Center for Astrophysics

  10. Can we have superfluidityin a Fermi gas?

  11. 1911: Discovery of Superconductors • Discovery of Superconductivity in Metals HeikeKamerlingh-Onnes Resistance Temperature Nobel prize 1913

  12. Superfluids Superconductors Flow without friction Current without resistance • No energy loss • persistent currents • expels magnetic fields • No energy loss • persistent flow • Doesn’t want to rotate Onnes 1911Müller & Bednorz 1987 Onnes 1908,Kapitza, Allen & Misener 1938

  13. What are superconductors? • Apparently the electrical current flows without friction • But: Carrier of electrical current are Electrons  Electrons are Fermions

  14. What are superconductors? • Apparently the electrical current flows without friction • But: Carrier of electrical current are Electrons  Electrons are Fermions L. Cooper (1956) (45 years after Onnes): Pairing of electronsPairs are Bosons  Superconductivity: Condensation of Electron Pairs J. Bardeen, L. Cooper, R. Schrieffer (BCS), 1957, Nobel prize 1972

  15. Fermionic Superfluidity John Bardeen Leon N. Cooper John R. Schrieffer Condensation of Fermion Pairs Superconductors: Charged superfluids of electron pairs Frictionless flow  Resistance-less current

  16. High-temperature Superconductors J. Georg Bednorz K. Alex Müller Critical temperature: 35 K above Absolute Zero (-238 °C) Record today: 138 K (-135 °C) Nobel prize 1987

  17. Room temperature superconductors? • Today: • ~5-10% energy loss only due to transport of energy • The hope: • Superconducting cables • No resistance No energy loss during transport We need: A model system for superconductors Ultracold atomic gases The problem: High-temperature superconductivity not really understood Electrons interact so strongly that it’s hard to model

  18. Can we do this with atoms? YES! The ultracold Fermi gas at MIT: • Lithium-6 (3p, 3n, 3e-) is a fermion • The atoms form pairs likeelectrons in a superconductor • Size of pairs isfreely controllable • The gas becomes superfluid

  19. How can you distinguish a superfluid from a normal one?

  20. Rotating buckets • Rotating bucket Super Normal Fluid Fluid

  21. Rotating superfluid Superfluid does not want to rotate Only possibility:Vortices, “Mini-Tornados”, “Quantum whirlpools” Superfluids are described by matter wave The wave has to close in itself(Example: Vibrating rubber band) Only full wavelengths lare allowed Circulation is only possible in certainunits (“Quanta”), carried by the Vortices

  22. Vortex structure Look from top into the bucket

  23. Vortex structure Look from top into the bucket Aleksei A. Abrikosov Nobel prize 2003 Abrikosov lattice (honeycomb lattice)

  24. Vortex latticesin bosonic gases/fluids Berkeley (R.E. Packard, 1979) Helium-4 ENS (J. Dalibard, 2000) Rubidium BEC

  25. Rotation of a neutral Fluid Coriolis Force Superconductor in a magnetic field Lorentz Force U. Essmann and H. Träuble,Physics Letters A, 24, 526 (1967)

  26. Demonstration of superfluidity in a Fermi gas Ultracold gas

  27. Vortices in the BEC-BCS Crossover Vortex lattices • Demonstration of superfluidity in a gas of atom pairs • A high-temperature superfluid - 0.7 B Pair size Scaled to the density of electrons in a metal, the gaswould become superfluid far above room temperature M.W. Zwierlein, J.R. Abo-Shaeer, A. Schirotzek, C.H. Schunck, W. Ketterle, Nature 435, 1047-1051 (2005)

  28. Fermionic Superfluidity withImbalanced Spin Populations What if there are too many singles?

  29. Fermionic Superfluidity with Imbalanced Spin Populations |1> |2> 0% 6% 12% 22% 30% 56% 90% 94%

  30. What is the Nature of the Imbalanced State?

  31. Direct observation of the density difference Cooling Down Normal Superfluid Y. Shin, M.W. Zwierlein, C.H. Schunck, A. Schirotzek, W. Ketterle, PRL 97, 030401 (2006)

  32. Reconstruction of 3D density profile Only assumption: cylindrical symmetry d = 0.6 Phase Separation ! Fermionic Superfluidity does not tolerate loners

  33. Gallery of superfluid Gases Atomic Bose-EinsteinCondensates (Sodium) Molecular Bose-EinsteinCondensates (6Li2) Pairs of fermionic atoms(6Li)

  34. Ultracold Atoms As Model systems: • How does matter work?new quantum states,development of new materialsQuantum computer, Quantum simulators (Bose and Fermi gases) As measuring device: • Development of highly sensitive sensors gravitational gradient sensors (important for mining, geophysics),sensors for navigation • New highly accurate atomic clocks as time standardbasis of all GPS-systems, more accurate positioning, faster telecommunication requires accurate clocks

  35. The team BEC 1: Andre Schirotzek Ariel Sommer Fermi 1: Cheng-Hsun Wu Ibon Santiago Dr. Peyman Ahmadi Undergraduates: Caroline Figgatt Jacob Sharpe Sara Campbell Kevin Fischer 39K 40K 6Li

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