COLLISIONS IN ULTRACOLD METASTABLE HELIUM GASES

1. G. B. Partridge, J.-C. Jaskula, M. Bonneau, D. Boiron, C. I. Westbrook Laboratoire Charles Fabry de l’Institut d’Optique, Palaiseau France COLLISIONS IN ULTRACOLD METASTABLE HELIUM GASES

2. Methods, apparatus, He*. Experiments: 4-wave mixing of matter waves Outline • Motivation and Background • -Optics, atomoptics, quantum optics, quantum atom optics… Optical Trapping andRelative Number Squeezing Spin Mixtures

3. T. Pfau (Stuttgart) L. Deng et al. (NIST) Andrews et al Science,275 ,637,1997 Strecker et al. (Rice) Motivation, atom optics… Optics : Photons, waves… wave particle duality. Atomic physics  atom optics : i.e – slits, interferrometers, etc Bec  coherent atom optics: Atom Laser, fringes, + nonlinear atom optics (interactions): 4wm , solitons… Quantum atom optics? -ex’s correlations, squeezing, entanglement, teleportation… Use counting, single particles, statistics… -- Key is detection: metastable Helium (He*).

4. He* : What’s it hiding? The 23S1 state of He has a decay time ~ 8000 s !* *single atom ~ spin polarized (So what?) The stored energy of the metastable state is 19.8 eV/atom. e- This energy can kick off electrons & ionize atoms of surfaces that the atom meets. + Add in a potential, get an avalanche of electrons.  High gain amplifier = single atom sensitivity.

5. I I Trapping and Cooling He* • Laser cooling helium? • Behaves a lot like an alkali-metal. • (Cycling Optical Transition, magnetically trappable )

6. Single Atom Detection Use a micro-channel plate (many e- avalanche detectors in parallel) to give position information. Gather resulting electric pulses using crossed delay lines. Use relative arrival times to reconstruct atoms’ positions (time of flight) in 3D.

7. magnetic optical A new tool for He* Statistical measurements: 1000’s of repetitions. magnetic trap was not engineered for this… (although we try anyway) Long term: favors Optical Trap Also, better geometry: aligns long axis of potential ( short TOF, short correlation length) w/ high resolution direction, Z. TOF Gives freedom to try spin mixtures… First step towards more complicated potentials for He* (lattices, disorder etc.)

8. BEC of He* in the optical trap Transfer from magnetic trap after some pre-cooling: N = 5 x 106, T = 15 K Evaporate by reducing intensity of trap laser over ~ 4 sec. N0 = 105 r = 1.5 kHz, z = 8 Hz G. B. Partridge, J.-C. Jaskula, M. Bonneau, D. Boiron, C. I. Westbrook, Phys. Rev. A 81, 053631 (2010).

9. Quantum Optics: photon pairs

10. kS kS k0 k0 k0 k0 Matter Wave FWM: atom pairs Create an m = 0 condensate w/ raman pulse. Split BEC into two momentum components with Bragg pulse: +/- k0 S-wave interactions lead to spherical shell of scattered atoms at k=kS  spontaneous FWM

11. P(Δt) 0 Δt kS kS k0 k0 The “intuitive” result Scattered pairs are correlated… Like in photon pairs: “Enhanced coincidence rate when phase matching condition is met.”

12. (per atom) kS kS k0 k0 kS kS k0 k0 Beyond Optics: smaller sphere “energy balance” Energy gain from removal of atom from condensate mode Energy Cost to put atom into scattered mode (still overlapped w/ condensate). < |kS| < |k0| V. Krachmalnicoff, J.-C. Jaskula, M. Bonneau, V. Leung, G. B. Partridge, D. Boiron, C. I. Westbrook, P. Deuar, P. Zin, M. Trippenbach, K. Kheruntsyan, Phys. Rev. Lett. 104,150402 (2010).

13. Lesson Learned: Do Q.O. experiments using atoms, but be careful about simple 1:1 intuition. There are differences, for better or worse… Plus, the sphere’s not a sphere • After colliding, atoms still have to get out of the region of the condensates. • i.e. they roll down the mean field hill: V = 2g(r,t) • But the hill is collapsing out from under them. Anisotropy of BEC’s leads to directional acceleration Analogy? ponderomotive force in high harmonic generation (Balcou et al PRA 1997) Phys. Rev. Lett. 104,150402 (2010).

14. A B Heidmann et al. PRL 59 2555 (1987) Intermediate Q.O.: Relative N Squeezing Measurement of intensity noise between “twin” beams. Reduction in noise, 30% below the shot noise limit!

15. Back-to-Back Correlations: 3600 shots New Atom Pairs RF + Bragg pulse. Optical Trap BEC Collision along long axis + better repeatability gives improved S/N. Now what about squeezing?

16. 1 16 zones Matter Wave N Squeezing Divide scattered halo into sections, compare number difference in geometrically opposing zones to that of non-opposing zones. (for uncorrelated N, i.e. shot noise) M

17. Details… Detail 1: Raw data ~ -0.5 dB squeezing Why isn’t it perfect? (partly b/c its an experiment) Detail 2: Effect of of correlation length: ~Measurement bandwidth Specifically, the detector efficiency, , limits the measured variance. Perfect correlations: M = (1- ) • = 0.6 (“open area”) : -3 dB • = .13 (best estimate): -13 dB

18. What’s next?

19. RF transfers: spin mixtures Alternate Future: spin mixtures With optical trap, we can think about using different spin states (mJ = +1,-1,0) spin mixtures, spinor condensates … But!Trapped He* gases are prone to loss due to Ionization-enhanced inelastic loss processes. Spin Polarization in the mJ = 1 provides stabilization by ~5 orders of magnitude. What about other states and combinations of states? State specific loss constants unconfirmed experimentally (only mJ = 1 is magnetically trappable)

20. Loss Rates in a spin mixture • Inelastic Loss Experiment 1: • Put them all together and see what survives… “Large” loss rate: 00, ±1 “Small” loss rate: 01, 0-1, 11, -1-1 G. B. Partridge et al., Phys. Rev. A 81, 053631 (2010).

21. Quantitative Loss Rates Inelastic Loss Experiment 2: Make careful measure of the dominant processes 00 ±1. • 00 = 6.6(4) × 10 −10 cm3/s • ±1 = 7.4(10) × 10 −10 cm3/s.  Not necessarily prohibitive! (for certain things…) G. B. Partridge et al., Phys. Rev. A 81, 053631 (2010).

22. Summary • Quantum Atom Optics: Spontaneous FWM of deBroglie matter waves. • Don’t forget they’re atoms. • Relative Number Squeezing for correlated atom pairs. • Atomic version of a Quantum Optics Classic. • Spin Mixtures in of He* ? • Stay tuned…

23. Thanks! Questions?