1. Comparison of Methods to Load a Mirror Magneto-Optical Trap Date: 14 May 2009 Author: C. Erin Savell Advisors: Dr. Shaffer and Arne Schwettmann Acknowledgement: Jonathan Tallant, Adrienne Wade, Herbert Grotewohl, Ernest Sanchez Capstone Talk PHYS 4300

2. Outline Motivation Atom Interferometry Magneto Optical Trap (MOT) Cooling and trapping transition Mirror MOT My work o Measuring MOT characteristics o Measuring MOT loading rates o Discussion of results Questions http://weblogs.newsday.com/sports/watchdog/blog/satellite-radio.jpg http://www.aerospaceweb.org/aircraft/fighter/f22/f22_09.jpg

3. Motivation To streamline MOT formation process; better MOTs allow better atom chip experiments Atom chip allows faster, cheaper BEC (Bose-Einstein Condensate) formation o requires less equipment and gets steeper magnetic field gradients Atom interferometry can beat current methods used for inertial navigation by orders of magnitude, but systems need to be compact

4. Graphic courtesy of H. Grotewohl What is an Interferometer? Interferometer: instrument that separates beam of light into two and recombines them resulting in an interference pattern Resulting pattern can be used to measure wavelength, index of refraction, or astronomical distances (Measures Phase shifts -> phase to intensity conversion) A high precision method to measure speed of light and acceleration

5. Can be used for navigation gyroscope for inertial guidance o Will replace laser interferometers/gyroscopes Atom Interferometry more sensitive than with light = BETTER o Atoms move at finite speed << c o Longer sampling time o more time to experience inertial changes Atom Interferometry: Why Mirror assembly for laser interferometer www.answers.com/topic/michelson-interferometer Ring laser gyroscope Fiber optic gyroscope www.aerospaceweb.org/question/ weapons/q0187.shtml

6. Atom Interferometry: How Atom well formed in MOT or other similar means Radio frequency (RF) current passed through a nearby wire o Causes wavefunctions in trap to change shape, spliting from “single well” of atoms to “double well” Atom wavefunctions recombine o Absorption imaging can detect resulting interference pattern Graphic courtesy of H. Grotewohl Atomic Wave Functions (split-> superposition)

7. MOT Cooling and trapping: o Lasers create “Optical Molasses”: atoms absorb photon from one direction, then emit in all directions; repeats o Reduction of momentum and kinetic energy of atoms results = “cooling” o Magnetic field gives a spatially dependent absorption = “trapping” Graphic courtesy of H. Grotewohl Laser Orientation in a MOT (red= laser)

8. Photon ΔPΔP Atom ΔPΔP ΔPΔP Animation courtesy of Ernie Sanchez MOT Animation

9. Mirror MOT Same principle as a basic MOT, but uses a mirror to reflect the laser Easier for trapping atoms near a surface Provides good source of cold atoms for loading of atom chip microtraps o Atom chips can be used as the mirror in a mirror MOT Schmiedmayer Paper, p. 4 Atom chip surface Mirror MOT on atom chip (red= laser, gray=chip/mirror) Graphic courtesy of H. Grotewohl

10. Cooling and Trapping Transitions of Rb-87 http://jilawww.colorado.edu/pubs/thesis/du/ Cooling laser: red-detuned to compensate for Doppler shift Repumping laser: recycles atoms from ground state back into cooling transition

11. Our Mirror MOT Image courtesy of Arne Schwettmann MOT Future cooling block location Mirror (or atom chip mount) Rb-85 atoms in mirror MOT Located 4.8mm below mirror surface No chip in chamber yet; just mirror T=~200μK FWHM 1.6mm vertically, 0.6mm horizontally

12. Mirror MOT Chamber Setup CCD Camera Main Chamber Anti-Helmholtz Coils

13. Factors Affecting MOT Stability Background Pressure: ambient pressure inside chamber o Pressure too low -> smaller number of atoms in MOT o Pressure too high -> increased atom collisions shorten MOT lifetime by knocking atoms out of trap Laser Lock: o Necessity to minimize signal noise o Stable lock = stable MOT o No lock = no MOT

14. Rubidium Source Saes Getters S. p. A Catalog, p. 10 Image courtesy of Arne Schwettmann Source controlled by current Normally ~5.3A Attaches by a mount on a flange that has electrical feed-throughs Releases Rb from solid state to a gaseous state

15. My Work Goal: to make higher quality MOT for loading chip trap Count number of atoms in MOT o The more atoms the better Measure density of atoms in MOT o Denser is better Measure loading rate of MOT o Will compare rate and background pressure of 3 different MOT loading methods MOT in Shaffer Lab Image courtesy of Arne Schwettmann

16. Atom Number and Density in a MOT Calibrate photodiode with power meter (measure in volts) Measure intensity of light (power, P) emitted from MOT and detuning of laser beams with power meter Solve for P TOT Deduce the number of atoms by calculation Number of atoms and MOT volume used to calculate density VariableDescription a =lens focal length d =lens diameter α =reduction factor of glass P =measured power P a = P TOT = power per atom (constant) power emitted by MOT N =number of atoms in MOT

17. Photodiode Calibration Setup irislinear polarizerbeam splitter beam direction power meter photo diode

18. MOT Loading Rate Measurement Fast loading rate and low background pressure are goals Compare rates and background pressure of 3 loading methods: o Continuous: source on nonstop o Pulsed: source pulsed on/off o UV-LIAD (Ultra-violet Light Induced Adsorption Desorption): UV lamp used to desorb Rubidium atoms from windows/sides of chamber Diode lasers from MOT setup

19. Building a UV LED Array for UV-LIAD Built UV-LED array Assembled circuit to support LED array Tested circuit and assembled it in front of chamber window UV LED array circuit

20. Rubidium Source Continuously “on” Utilizes lower current (~3A) Slower, more controlled loading rate UV LIAD Rates Rubidium source switched off UV LED array switched on for entire loading period Rb atoms on chamber walls become excited, adsorb from walls into gas, load MOT

21. Pulsed Source Two separate pulse timing schemes considered: o 4s on, 16 seconds off with 5A current o 2s on, 18 seconds off with 10A current More intense current will induce faster loading rate Shorter pulse time keeps background pressure low, reducing background collisions of atoms in MOT Fast; allows for more experiments per block of time

22. Experimental Parameters The laser lockpoint was maintained at δ =-10.7±1.6MHz from the trapping transition 85 Rb 5 S 1/2 F = 3 5 P 3/2 F = 4 Background pressure of chamber was maintained near 2.0x10 -10 Torr Image courtesy of Arne Schwettmann F= 2 & 4 F= 3 & 4 F= 4

23. RESULTS

24. UV-LIAD, Continuous, and Background MOT Loading Methods Background rate is slowest UV-LIAD improves atom number by factor of 2 Continuous source best of the three Background fitted curve UV LIAD fitted curve UV LIAD Background pressure Continuous *Error in all data points measured is +/- 13%

25. Pulsed Source MOT Loading Methods 10A current pulse gives fastest loading rate o 10 times faster than continuous, fastest overall 5A current half has fast, twice as long, smaller atom number present in trap 2s pulse fitted curve 4s pulse fitted curve 4s pulse 2s pulse *Error in all data points measured is +/- 13%

26. Questions?

27. Winky says goodbye!

28. http://jilawww.colorado.edu/pubs/thesis/du/

31. Outline Background and Motivation What is a laser interferometer? Why use an atom interferometer? The Experiment Laser cooling and trapping Mirror MOT Wire trapping and evaporative cooling RF current application Absorption imaging The Apparatus My Part Questions

32. Our MOT Image courtesy of Arne Schwettmann Atom chip mount / mirror MOT Future cooling block location

33. If light interferometers are so great, why use atoms? Atom interferometers are more precise than the laser interferometers currently in use o because atom wavelengths are much shorter than photon wavelengths Ultra-cold atoms have great range of applications in aviation http://weblogs.newsday.com/sports/watchdog/blog/satellite-radio.jpg http://www.aerospaceweb.org/aircraft/fighter/f22/f22_09.jpg

34. The Experiment Atom sample must be ultra-cold Procedure needed to prepare sample: o Laser cooling and trapping of gaseous atoms: detuned lasers and magnetic fields o Mirror Magneto-optical trap (MOT): atoms trapped close to surface of atom chip o Wire trap: a stronger magnetic field applied to compress atoms closer together using current in small wires on surface o Evaporative cooling: cools atom sample to μK temperatures Graphic courtesy of H. Grotewohl Schmiedmayer Paper, p. 4 Mirror MOT on atom chip (red= laser, gray=chip)

35. The Apparatus

36. My Part Used Mathematica to model magnetic fields from wires and the resultant trapping potentials Align and lock lasers for MOT Work on experiment (atom chip design and assembly, absorption imaging, etc.)

37. Final statements Atom interferometers are more precise than the laser interferometers currently in use Future experiments for the apparatus: To form and manipulate a Bose-Einstein Condensate (BEC) of rubidium near the surface of an atom chip MOT in Shafer Lab