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Ultracold Atoms, Mixtures, and Molecules

Subhadeep Gupta. UW Physics 528, 25 Feb 2011. Ultracold Atoms, Mixtures, and Molecules . Ultracold Atoms. Formation of a Bose- Einstein condensate (BEC). High sensitivity ( large signal to noise, long interrogation times in a well known atomic system )

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Ultracold Atoms, Mixtures, and Molecules

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  1. Subhadeep Gupta UW Physics 528, 25 Feb 2011 Ultracold Atoms, Mixtures, and Molecules

  2. Ultracold Atoms Formation of a Bose- Einstein condensate (BEC) High sensitivity (large signal to noise, long interrogation times in a well known atomic system) Precision measurements (spectroscopy, fund sym, clocks) Sensing (accelerations, gravity gradients) Many-body aspects Quantum Fluids Condensed Matter Physics Nuclear Physics Quantum Engineering (Potentials and Interactions) Quantum Information Science Quantum Simulation Ultracold Molecules (through mixtures)

  3. Ultracold Atoms and Molecules at UW A dual-species experiment (Li-Yb) for making and studying ultracold polar molecules and for probing strongly interacting Fermi gases Development of precision BEC interferometry (Yb) for fine structure constant a and test of QED

  4. Quantum Degeneracy in a gas of atoms N atoms V volume T temperature (Dp)3 ~ (m kB T)3/2 (Dx)3 ~ V h3 h3 n ~ 1 (m kB T)3/2 1 atom per quantum state (available position space) (available momentum space) Number of atoms = Quantum Phase Space Density (n=N/V) Air n ~ 1019/cm3, Tc ~ 1mK Stuff n ~ 1022/cm3, Tc ~ 0.1K Dilute metastable gases n ~ 1014/cm3 Tc ~ 1mK !! Ultracold !! Everything (except He) is solid and ~ non-interacting

  5. Laser cooling Evaporative cooling - - 6 9 1 1 0 0 ABSOLUTE TEMPERATURE (log Kelvin scale) s u r f a c e o f s u n 3 1 0 r o o m t e m p . l i q u i d Nitrogen BCS superconductors, 4He superfluid, CMB fractional quantum hall effect 0 1 0 J o u l e - T h o m p s o n e x p a n s i o n 3 4 H e - H e d i l u t i o n 3 s u p e r f l u i d H e - 3 1 0 d i l u t e B p-wave threshold a d i a b a t i c d e m a g n e t i z a t i o n Degenerate Gas d i l u t e B E C Depth of atom traps atomic interactions Zero point energy

  6. Laser Cooling P S => COOLING ! z I s- s- s+ x s- s+ s+ y I Magneto-Optical Trap (MOT) “Workhorse” of laser cooling Atom Source ~ 600 K; UHV environment (Need a 2 level system)

  7. Evaporative Cooling in a Conservative Trap V 2 -1/2V Optical Dipole Trap pre collision postcollision wL << wres mK V  0 Depth ~ I/D; Heating Rate ~ I/D2

  8. Evaporative Cooling in a Conservative Trap V 2 -1/2V Optical Dipole Trap pre collision postcollision wL << wres mK V  0 Depth ~ I/D; Heating Rate ~ I/D2

  9. Imaging the Atoms Imaging atoms (Formation of a Rb BEC, UC Berkeley 2005)

  10. Landmark achievements in ultracold atomic physics Superfluidity / observation and study of a vortex lattice (Dalibard, Ketterle, Cornell) Bose-Einstein condensation (JILA, MIT, Rice….) Macroscopic coherence (Ketterle) Superfluid to Mott-insulator quantum phase transition (Hansch)

  11. Landmark achievements in ultracold atomic physics Degenerate Fermi gas Molecular Bose-Einstein condensate (Jin, Hulet, Thomas, Ketterle, Grimm) Superfluidity of Fermi pairs

  12. Ultracold Polar Molecules Realization of new quantum gases based on precise particle manipulation and strong, long-range, anisotropic, interparticle dipole-dipole interactions (1/r3 vs 1/r6 “contact” potential) Quantum Computing and Simulation Enhanced electric dipole moment sensitivity for tests of fundamental symmetries Precision Molecular Spectroscopy for clocks, time variations of fundamental constants, others. Cold and ultracold controlled Chemistry

  13. Polar (diatomic) Molecules from Ultracold Atoms

  14. New degrees of freedom bring with them scientific advantages New degrees of freedom bring with them technical issues Unequal sharing of electrons Polarizable at relatively low field Polar (diatomic) Molecules from Ultracold Atoms

  15. Ultracold Atom Menu Very different mass, very different electronic structure  strong dipole moment

  16. Selected Molecular Constituents Various species-selective manipulation methods Interaction tuning through Feshbach resonances Yb as an impurity probe of the Li Fermi superfluid. Large mass difference mixture of interacting fermions Photo- and magneto-association as starting point for making diatomics Several Fermi/Bose isotopes available

  17. Selected Molecular Constituents Large difference in electronic structure and mass  Large electric dipole moment and strong, anisotropic interactions Bosonic or Fermionic Molecules can be formed Paramagnetic + Diamagnetic Atom  Molecular ground state will also have magnetic moment. Can be magnetically manipulated and trapped. Paramagnetic ground state, heavy component  candidate for electron EDM search Quantum computing candidate

  18. Dual Species Apparatus Pump Area Yb Zeeman Slower Yb Oven Ultrahigh Vacuum (UHV < 10-10 Torr) Main Chamber Li Zeeman Slower AGENDA Cool and trap Li and Yb Study interacting mixture Induce controlled interactions Form molecules Li Oven

  19. 2-species Magneto-Optic trap Sequential Loading Ytterbium – green, Lithium - red The 2 MOTs are optimized at different parameters of magnetic field gradient and also exhibit inelastic interactions

  20. Optical Dipole Trap Absorption image of optically trapped lithium atoms together with uncaptured atoms released from a MOT

  21. Evaporative Cooling of Bosonic 174Yb Temperature evaluated from size of absorption imaged atoms after variable time of flight With forced evaporative cooling, can cool towards quantum degeneracy s-wave scattering length = 5.5nm

  22. “Feshbach molecule” formation Strong Interactions in Fermionic Lithium Feshbach resonance between |1> and |2>

  23. Collisional Properties of the LiYb Mixture Ytterbium Lithium Elastic interactions dominate forming a stable mixture. From the timescale of the thermalization process, we extract the interspecies collisional cross-section and s-wave scattering length magnitude of 13 bohrs. Establishment of a new two-species mixture.

  24. Sympathetic Cooling of Lithium by Ytterbium T/TF = 0.7 With improvements to cooling procedures (in progress), double degeneracy should be possible

  25. Ultracold Molecules through PhotoAssociation Scan Trap loss measurement in the 6Li system Provides information on excited potential First step towards ground LiYb molecule

  26. Future Li-Yb Work UltracoldStable Mixture Simultaneous degeneracy Yb as probe of Feshbach molecules Yb as probe of Fermi superfluid Induce strong Li-Yb interactions Photoassociation in LiYb system Scan 2 photon PA + 2 photon Raman Ground state polar molecules through multiple2-photon processes,

  27. neutron interferometry h/mn ac Josephson effect Quantum Hall effect g-2 of electron + QED atomic physics route - 2 5 0 - 2 0 0 - 1 5 0 - 1 0 0 - 5 0 0 5 0 1 0 0 1 5 0 2 0 0 æ - 1 a i n p p b – 1 ç - 1 a è 9 8 Precision Measurement of Fine Structure Constant a Cross-field comparisons Precision test of QED (2000) (2008)

  28. motivation2 BEC is a bright coherent source for atom interferometry QED-free Atomic Physics Route to  0.008 ppb: hydrogen spectroscopy, (Udem et al.,1997; Schwob et al.,1999) Penning trap mass spectroscopy Frequency comb - Cs (Berkeley) Rb (Paris) 0.7 ppb: penning trap mass spectr. (Beier et al., 2002)

  29. The phase of the matter wave grating is encoded in oscillating contrast. The phase of the contrast signal for various T gives rec. Contrast Interferometry with a BEC principle2 • Advantages: • no sensitivity to mirror vibrations, ac stark shift, • rotation, magnetic field gradients • quadratic enhancement with additional momenta • (x N2) • single shot acquisition of interference pattern

  30. Contrast Interferometry with a BEC principle2 Na BEC 2002 The phase of the matter wave grating is encoded in oscillating contrast. The phase of the contrast signal for various T gives rec.

  31. Contrast Interferometry with a BEC principle2 Na BEC 2002 With Na BEC experiment 7ppm precision achieved, but inaccuracy at 200ppm, attributed to mean field.

  32. Contrast Interferometry with a BEC Scale Up Increase sensitivity by increasing momenta of 1 and 3 by 20-fold and increasing T We then expect sub-ppb precision in less than a day of data. Use of a Yb BEC – no B field sensitivity and multiple isotopes for systematic checks At this level, have to very carefully account for atomic interactions and the mean field shift. Theoretical analysis performed in collaboration with Nathan Kutz (AMath). Gearing up for the experiment - expect the next generation result in 2-3 years.

  33. UW Ultracold Atoms Team $$$ - NSF, Sloan Foundation, UW RRF, NIST Undergrad Students: Jason Grad, Jiawen Pi, Eric Lee-Wong Grad Students: Anders Hansen, Alex Khramov, Will Dowd, Alan Jamison Post-doc: Vladyslav Ivanov

  34. One- and Two- Electron Atoms 6Lithium

  35. Yb (Crossed)Beam Spectroscopy Fluor [arb] Freq [MHz] Fluor [arb] Freq [MHz]

  36. Magneto-Optical Trapping of Li Fluor (arb) Size (mm) few x 108 atoms loaded in a few seconds Temp ~ 400mK Load time (s) Expansion time (ms)

  37. Ultracold Mixtures of Lithium and Ytterbium Atoms Preliminary Evidence of Elastic Interactions

  38. Ultracold Atoms High sensitivity (large signal to noise, long interrogation times in a well known atomic system) Precision measurements (spectroscopy, fund sym, clocks) Sensing (accelerations, gravity gradients) Many-body aspects Quantum Fluids Condensed Matter Physics Nuclear Physics Quantum Engineering (Potentials and Interactions) Quantum Information Science Quantum Simulation Ultracold Molecules (through mixtures)

  39. Some major achievements in ultracold atomic physics Bose-Einstein condensation (JILA, MIT, Rice….) Macroscopic coherence Superfluidity / observation and study of a vortex lattice Degenerate Fermi gas

  40. Evaporative Cooling of Fermionic Lithium vacuum limited lifetime ~ 40 secs

  41. Evaporative Cooling of Bosonic 174Yb Plain evaporation at B=0 N ~ up to 106 (here ~ 3 x 105) Side view of released Yb N ~ 50,000 With forced evaporation, can reach sub-microKelvin Here, temp X 2 above degeneracy for 50,000 atoms

  42. Dual Species Apparatus 1 inch

  43. Optical Dipole Trap Shallow angle (10 degrees) crossed beam dipole trap 1064nm, up to 50 Watts

  44. LiYb Molecule: Theory ~ 0.4 Debye Electric dipole moment Svetlana Kotochigova, Temple Univ/ NIST preliminary results Peng Zhang, ITAMP Harvard

  45. Fermi Degeneracy in 6Li TF T (calc) T (meas) Top view of Trapped Li With evaporation at 300 G, can achieve T/TF ~ 0.5 Size gets clamped by the Fermi Diameter DF

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