Quantum Physics & Ultra-Cold Matter

Quantum Physics & Ultra-Cold Matter Seth A. M. Aubin Dept. of Physics College of William and Mary December 16, 2009 Washington, DC

Outline • Quantum Physics: Particles and Waves • Intro to Ultra-cold Matter  What is it ?  How do you make it ?  Bose-Einstein Condensates  Degenerate Fermi Gases • What can you do with ultra-cold matter

Quantum Physics Summary or “take home message”: 1. It’s weird  defies everyday common sense.

Quantum Physics Summary or “take home message”: 1. It’s weird  defies everyday common sense. 2. LIGHT behaves as both a PARTICLE and a WAVE.

Quantum Physics Summary or “take home message”: 1. It’s weird  defies everyday common sense. 2. LIGHT behaves as both a PARTICLE and a WAVE. 3. Matter (i.e. atoms) behaves as both a PARTICLE and a WAVE.

Quantum Physics Summary or “take home message”: 1. It’s weird  defies everyday common sense. 2. LIGHT behaves as both a PARTICLE and a WAVE. 3. Matter (i.e. atoms) behaves as both a PARTICLE and a WAVE. 4. If something is in 2 PLACES AT ONCE, then it will INTERFERE.

Quantum Physics Summary or “take home message”: 1. It’s weird  defies everyday common sense. 2. LIGHT behaves as both a PARTICLE and a WAVE. 3. Matter (i.e. atoms) behaves as both a PARTICLE and a WAVE. 4. If something is in 2 PLACES AT ONCE, then it will INTERFERE. 5. Quantum physics is science’s most accurate theory.

Electron’s g-factor: ge = 2.002 319 304 362 12-digits [Wikipedia, 2009] Quantum Accuracy Theory and experiment agree to 9 digits.

Light as a wave LASER source Screen

Path A Path B  Light as a wave LASER source

LASER source screen Light as a wave

Also works for single photons !!! [A. L. Weiss and T. L. Dimitrova, Swiss Physics Society, 2009.] Experiment uses a CCD camera (i.e. sensor in your digital camera).

LASER source path A screen path B Photons follow 2 paths simultaneously

… but, Matter is a

mK μK nK p p p x x x What’s Ultra-Cold Matter ? • Very Cold  Typically nanoKelvin – microKelvin  Atoms/particles have velocity ~ mm/s – cm/s • Very Dense … in Phase Space Different temperatures Same phase space density Higher phase space density

[priceofoil.org, 2008] How cold is Ultra-Cold? 1000 K room temperature, 293 K K Antarctica, ~ 200 K mK Dilution refrigerator, ~ 2 mK μK Ultra-cold quantum temperatures nK

Room temperature Quantum régime Ultra-cold Quantum Mechanics • Room temperature: • Matter waves have very short wavelengths. • Matter behaves as a particle. • Ultra-Cold Quantum temperatures: • Matter waves have long wavelengths. • Matter behaves as a wave.

Quantum Statistics Bosons Fermions Integer spin: photons, 87Rb. ½-integer spin: electrons, protons, neutrons, 40K. Bose-Einstein Condensate (BEC) All the atoms go to the absolute bottom of trap. Degenerate Fermi Gas (DFG) Atoms fill up energy “ladder”.

How do you make ULTRA-COLD matter? Two step process: 1. Laser cooling  Doppler cooling  Magneto-Optical Trap (MOT) 2. Evaporative cooling  Micro-magnetic traps  Evaporation

Magneto-Optical Trap (MOT) ~ 100 K

Iz [Figure by M. Extavour, U. of Toronto] Micro-magnetic Traps • Advantages of “atom” chips: • Very tight confinement. • Fast evaporation time. • photo-lithographic production. • Integration of complex trapping potentials. • Integration of RF, microwave and optical elements. • Single vacuum chamber apparatus.

Remove most energetic (hottest) atoms Wait for atoms to rethermalize among themselves Evaporative Cooling Macro-trap: low initial density, evaporation time ~ 10-30 s. Micro-trap: high initial density, evaporation time ~ 1-2 s.

P(v) Remove most energetic (hottest) atoms v Wait for atoms to rethermalize among themselves Evaporative Cooling Wait time is given by the elastic collision rate kelastic =n  v Macro-trap: low initial density, evaporation time ~ 10-30 s. Micro-trap: high initial density, evaporation time ~ 1-2 s.

RF@1.660 MHz: N=1.4x105, T<Tc RF@1.725 MHz: N = 6.4x105, T~Tc RF@1.740 MHz: N = 7.3x105, T>Tc 87Rb BEC

RF@1.660 MHz: N=1.4x105, T<Tc RF@1.725 MHz: N = 6.4x105, T~Tc RF@1.740 MHz: N = 7.3x105, T>Tc Surprise! Reach Tc with only a 30x loss in number. (trap loaded with 2x107 atoms)  Experimental cycle = 5 - 15 seconds 87Rb BEC ~ 500 nK

1925: A. Einstein predicts a low temperature phase transition, in which particles condense into a single quantum state. 1924: S. N. Bose describes the statistics of identical boson particles. 1995: E. Cornell, C. Wieman, and W. Ketterle observe Bose-Einstein condensation in 87Rb and 23Na. BEC History

“Iceberg” BEC Fermi Sea Fermions: Sympathetic Cooling Problem: Cold identical fermions do not interact due to Pauli Exclusion Principle.  No rethermalization.  No evaporative cooling. Solution: add non-identical particles  Pauli exclusion principle does not apply. We can cool fermionic 40K atoms sympathetically with an 87Rb BEC.

Sympathetic Cooling Low temperature Quantum Behavior “High” temperature

Atom Interferometry Spatial interferometry  Precision measurements of forces. Time-domain interferometry  atomic clock.

BEC Interferometry

D1 Path A Path B D2 Spatial Atom Interferometry IDEA: replace photon waves with atom waves.  atom photon Example: 87Rb atom @ v=1 m/s  atom  5 nm. green photon  photon  500 nm. 2 orders of magnitude increase in resolution at v=1 m/s !!! Mach-Zender atom Interferometer:

Atomic Clocks • Special type of atom interferometer. • Temporal interference, instead of spatial. • Most accurate time keeping devices that exist. • State-of-the-art: accuracy of 1 part in 1016 … 16 digits !!! • Applications: • Keeping time. • GPS Navigation. • Deep space navigation.

Summary • Quantum Physics. • Ultra-cold atom technology. • Matter-wave interferometry.

Francesca Fornasini Prof. Seth Aubin Lab: room 15 Office: room 333 saaubi@wm.edu Austin Ziltz Yudistira Virgus Jim Field Ultra-cold atoms group Brian Richards Megan Ivory

Colors: Staff/Faculty Postdoc Grad Student Undergraduate S. Myrskog L. J. LeBlanc M. H. T. Extavour A. Stummer T. Schumm B. Cieslak J. H. Thywissen D. McKay Thywissen Group

Quantum Physics & Ultra-Cold Matter