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

Einstein condensate (BEC) 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) Formation of a Bose- Einstein condensate (BEC) Verifying known Hamiltonians, generating new Hamiltionians, quantum simulations, new entities 2

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

Dilute metastable gases n ~ 1014/cm3 Quantum Degeneracy in a gas of atoms 1 atom per quantum state N atoms V volume T temperature (Dx)3 ~ V (Dp)3 ~ (m kB T)3/2 (available position space) (available momentum space) Number of atoms = h3 n (m kB T)3/2 h3 ~ 1 Quantum Phase Space Density (n=N/V) Density n=N/V. Thinner than air. Make equations explicit. Metastable -> gas for a while -> if within this time you can cool it down to a microK, you’re set… 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

ABSOLUTE TEMPERATURE (log Kelvin scale) f a c e o f s u n 3 1 Laser cooling Evaporative cooling r o o m t e m p . l i q u i d Nitrogen BCS superconductors, 4He superfluid, CMB fractional quantum hall effect J o u l e - T h o m p s o n e x p a n s i o n 1 3 H e - 4 H e d i l u t i o n s u p e r f l u i d 3 H e - 3 1 d p-wave threshold i l u t e B a d i a b a t i c d e m a g n e t i z a t i o n Introduce s-wave scattering length with p-wave threshold. The scattering length can be manipulated using internal energy tricks. Introduce ease of manipulation with energy scales. Gauss, Bohr magneton, optical trapping. Sufficient trap depth obtained with modest magnetic fields and detuned light. Atomic interactions can be tuned up as well. Mention at this point that the range of control offered by atomic physics techniques – trapping, dimensionality, temperature, spin composition etc. 1 - 6 d Degenerate Gas i l u t e B E C Depth of atom traps atomic interactions 1 - 9 Zero point energy

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

Evaporative Cooling in a Conservative Trap pre collision post collision Optical Dipole Trap wL << wres Depth ~ I/D; Heating Rate ~ I/D2 Usually DC magnetic, now optical quite common, AC magnetic, RF and microwave dressing, etc. mK

Evaporative Cooling in a Conservative Trap Optical Dipole Trap wL << wres Depth ~ I/D; Heating Rate ~ I/D2 pre collision post collision mK V  0

Imaging the Atoms (Formation of a Rb BEC, UC Berkeley 2005) Imaging atoms Imaging the Atoms Stolen from post-doc days Procedure takes about 1 minute. Formation of a dense dark core at sufficiently low (few hundred nK) temp. mention pulsed experiment. As temperature is lowered etc.. This sort of imaging is destructive - all the work descrived here (Formation of a Rb BEC, UC Berkeley 2005)

Landmark achievements in ultracold atomic physics Bose-Einstein condensation (JILA, MIT, Rice….) Macroscopic coherence (Ketterle) Superfluidity / observation and study of a vortex lattice (Dalibard, Ketterle, Cornell) Coherent and Superfluid! 2001 Nobel Prize Superfluid to Mott-insulator quantum phase transition (Hansch)

Landmark achievements in ultracold atomic physics Degenerate Fermi gas Molecular Bose-Einstein condensate Mention myself with respect to strongly interacting fermions. Recently, - other branches of physics: Efimov states, Kosterliz-Thouless transition – note that Efimov and Thouless are both at Washington. (Jin, Hulet, Thomas, Ketterle, Grimm) Superfluidity of Fermi pairs

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 Refer Krems, Shapiro, Madison, other folks… really don’t need this motivational slide in this milieu, nonetheless for the sake of completeness

Polar (diatomic) Molecules from Ultracold Atoms Need to draw energy levels versus electric field. Simple case of diatomic

Polar (diatomic) Molecules from Ultracold Atoms Unequal sharing of electrons Polarizable at relatively low field New degrees of freedom bring with them scientific advantages New degrees of freedom bring with them technical issues Shifting Gears picture… You have to indulge me a bit…. Need to draw energy levels versus electric field.

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

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

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 Distinctions from bi-alkalis.

Dual Species Apparatus Li Oven Li Zeeman Slower Yb Oven Yb Zeeman Main Chamber Pump Area Ultrahigh Vacuum (UHV < 10-10 Torr) Bucket windows for magnetic quadrupole and Feshbach coils. Photo of installed magnetic coils. AGENDA Cool and trap Li and Yb Study interacting mixture Induce controlled interactions Form molecules

Ytterbium – green, Lithium - red 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

Optical Dipole Trap More Li in trap pictures. Showing original position of atoms. Absorption image of optically trapped lithium atoms together with uncaptured atoms released from a MOT

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

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

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.

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

Ultracold Molecules through PhotoAssociation Scan Great success in bi-alkali KRb system (JILA) Trap loss measurement in the 6Li system Provides information on excited potential First step towards ground LiYb molecule

Ground state polar molecules 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 Scan 2 photon PA + 2 photon Raman Photoassociation in LiYb system Ground state polar molecules through multiple2-photon processes,

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

BEC is a bright coherent source for atom interferometry QED-free Atomic Physics Route to  motivation2 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) BEC is a bright coherent source for atom interferometry

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

principle2 Contrast Interferometry with a BEC 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.

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

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.

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

One- and Two- Electron Atoms 6Lithium

Yb (Crossed)Beam Spectroscopy Fluor [arb] Freq [MHz] Label all the transitions? Note the linewidths. Fluor [arb] Freq [MHz]

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

Ultracold Mixtures of Lithium and Ytterbium Atoms Preliminary Evidence of Elastic Interactions Yb lifetime is a bit lower than otherwise.hg

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) Verifying known Hamiltonians, generating new Hamiltionians, quantum simulations, new entities

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

Evaporative Cooling of Fermionic Lithium vacuum limited lifetime ~ 40 secs

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

Dual Species Apparatus Omitting up-down beams for clarity 1 inch

Optical Dipole Trap Shallow angle (10 degrees) Omitting up-down beams for clarity Shallow angle (10 degrees) crossed beam dipole trap 1064nm, up to 50 Watts

LiYb Molecule: Theory ~ 0.4 Debye Electric dipole moment Exotic molecule – unknown spectrum. Preliminary ab-initio theory. First help from Roman Krems. Unknown spectrum. Svetlana Kotochigova, Temple Univ/ NIST preliminary results Peng Zhang, ITAMP Harvard

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