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“When freezing cold is not cold enough - new forms of matter close to absolute zero temperature” Wolfgang Ketterle Massachusetts Institute of Technology MIT-Harvard Center for Ultracold Atoms 9/2/09 Meridian Lecture Space Telescope Science Institute Baltimore Quantum Gases The coldest matter in the universe What is temperature? A measure of energy One form of energy is motion (kinetic energy). Cold particles move slowly Hot particles are fast What is the lowest temperatures possible? Zero degree Kelvin (-273 degrees Celsius, -460 degrees Fahrenheit) is the zero point for energy The highest temperature is infinite (In principle it is possible for particles to have arbitrarily high kinetic energies – until they become so heavy (due to E=mc2) that they from a black hole – at the Planck temperature of 1032 K) What is the difference in temperature between summer and winter? 20 % How cold is interstellar space? 3K How cold is it in our laboratories? Nanokelvin: A billion times colder than interstellar space Why can you make new discoveries at cold temperatures? What happens to atoms at low temperatures? They slow down 600 mph (300 m/sec) 1 cm/sec They march in lockstep Matter made of waves! Population per energy state What is Bose Einstein Condensation? Bose-Einstein distribution T=Tc Energy Population per energy state What is Bose Einstein Condensation? T<Tc Condensate! Bose-Einstein distribution Energy Population per energy state What is Bose Einstein Condensation? T<Tc Condensate! Bose-Einstein distribution Energy Ordinary light Photons/atoms moving randomly Laser light Photons/atoms are one big wave * 1925 Gases (Atoms and Molecules) 1 n( ) e ( ) k BT 1 1 e k BT 1 Black-Body Radiation “Photons” Max Planck The cooling methods • Laser cooling • Evaporative cooling Hot atoms Hot atoms Laser beams Hot atoms Fluorescence Laser beams Fluorescence Laser beams If the emitted radiation is blue shifted (e.g. by the Doppler effect) …. Cold atoms: 10 – 100 K Fluorescence Laser beams Chu, Cohen-Tannoudji, Phillips, Pritchard, Ashkin, Lethokov, Hänsch, Schawlow, Wineland … Laser cooling 2.5 cm Evaporative cooling Phillips et al. (1985) Pritchard et al. (1987) One challenge … experimental complexity Sodium laser cooling experiment (1992) Sodium BEC I experiment (2001) Dan Kleppner Tom Greytak Dave Pritchard I.I. Rabi PhD Norman Ramsey PhD Dan Kleppner PhD PhD PhD Dave Pritchard Postdoc Bill Phillips PhD Eric Cornell Undergraduate Postdoc Wolfgang Ketterle Randy Hulet Carl Wieman Key factors for success: • Funding • Technical infrastructure • Excellent collaborators • Tradition and mentors How do we show that the Bose-Einstein condensate has very low energy? The condensate • a puff of gas • 100,000 thinner than air • size comparable to the thickness of a hair • magnetically suspended in an ultrahigh vacuum chamber How to measure temperature? Gas Effusive atomic beam Kinetic energy mv2/2 = kBT/2 How to measure temperature? Gas Effusive atomic beam Kinetic energy mv2/2 = kBT/2 CCD CCD Ballistic expansion: direct information about velocity distribution CCD Ballistic expansion: direct information about velocity distribution Absorption image: shadow of atoms The shadow of a cloud of bosons as the temperature is decreased (Ballistic expansion for a fixed time-of-flight) Temperature is linearly related to the rf frequency which controls the evaporation Distribution of the times when data images were taken during one year between 2/98-1/99 Key factors for success: • Some funding • Technical infrastructure • Excellent collaborators • Tradition and mentors Key factors for success: • Some funding • Technical infrastructure • Excellent collaborators • Tradition and mentors • Physical endurance How can you prove that atoms march in lockstep? Atoms are one single wave Atoms are coherent One paint ball on a white wall Two Paint does not show wave properties One laser beam on a white wall Light shows wave properties One laser beam on a white wall Two Fringe pattern: Bright-dark-bright-dark Light shows wave properties Two condensates ... 50 m Interference of two Bose-Einstein condensates Andrews, Townsend, Miesner, Durfee, Kurn, Ketterle, Science 275, 589 (1997) How do we show that the gas is superfluid? Rigid body: Vortices in nature Spinning a Bose-Einstein condensate The rotating bucket experiment with a superfluid gas 100,000 thinner than air Rotating green laser beams Two-component vortex Boulder, 1999 Single-component vortices Paris, 1999 Boulder, 2000 MIT 2001 Oxford 2001 J. Abo-Shaeer, C. Raman, J.M. Vogels, W.Ketterle, Science, 4/20/2001 Current Research BEC on a microchip Loading sodium BECs into atom chips with optical tweezers 44 cm BEC arrival BEC production T.L.Gustavson, A.P.Chikkatur, A.E.Leanhardt, A.Görlitz, S.Gupta, D.E.Pritchard, W. Ketterle, Phys. Rev. Lett. 88, 020401 (2002). Atom chip with waveguides Splitting of condensates 1mm One trapped 15ms condensate Expansion Two condensates Splitting of condensates 1mm Trapped 15ms expansion Two condensates Splitting of condensates Two condensates Y. Shin, C. Sanner, G.-B. Jo, T. A. Pasquini, M. Saba, W. Ketterle, D. E. Pritchard, M. Vengalattore, and M. Prentiss: Phys. Rev. A 72, 021604(R) (2005). Splitting of condensates Two condensates Atom interferometry: The goal: Matter wave sensors Use ultracold atoms to sense Rotation Navigation Gravitation Geological exploration Current Research Cold molecules Cold fermions Can electrons form a Bose-Einstein condensate and become superfluid (superconducting)? Two kinds of particles • Bosons: Particles with an even number of protons, neutrons and electrons • Fermions: odd number of constituents Only bosons can Bose-Einstein condense! Can electrons form a Bose-Einstein condensate and become superfluid (superconducting)? Two kinds of particles • Bosons: Particles with an even number of protons, neutrons and electrons • Fermions: odd number of constituents Only bosons can Bose-Einstein condense! How can electrons (fermions) condense? They have to form pairs! Can we learn something about superconductivity of electrons from cold atoms? Yes, by studying pairing and superfluidity of atoms with an odd number of protons, electrons and neutrons BEC of Fermion Pairs (“Molecules”) These days: Up to 10 million condensed molecules Boulder Innsbruck MIT Paris Rice, Duke Nov ‘03 Nov ‘03, Jan ’04 Nov ’03 March ’04 M.W. Zwierlein, C. A. Stan, C. H. Schunck, S.M. F. Raupach, S. Gupta, Z. Hadzibabic, W.K., Phys. Rev. Lett. 91, 250401 (2003) Gallery of superfluid gases Atomic Bose-Einstein condensate (sodium) Molecular Bose-Einstein condensate (lithium 6Li2) Pairs of fermionic atoms (lithium-6) Ultracold atoms A “toolbox” for designer matter Normal matter • Tightly packed atoms • Complicated Interactions • Impurities and defects Ultracold atoms A “toolbox” for designer matter Matter of ultracold atoms • 100 million times lower density • Interactions understood and controlled • no impurities • exact calculations possible Need 100 million times colder temperatures
