Sympathetic Laser Cooling of Molecular Ions to the μK regime C. Ricardo Viteri and Kenneth Brown Georgia Institute of Technology, School of Chemistry and Biochemistry and Computational Science and Engineering Division Atlanta, GA 30332, USA June 17, 2008

Chemistry and Ion Traps Takashi Baba and Izumi Waki Jpn. J. Appl. Phys., 35, L (1996) 24 Mg + + air  NH + 4, H 3 O +, C 2 H 5 +, COH +, N 2 H +, O 2 + (~7 K) o M. Welling, et al., Int. J. Mass Spectrom. Ion Processes, 172, 95 (1998) 24 Mg + + C 60 (collision energies up to 200 eV.) o K. Mølhave and M. Drewsen, Phys. Rev. A, 62, R (1998) Mg + (3p) + H 2 (D 2 )  MgH 2 + (MgD 2 + ) ~ 100 mK o H. A. Schuessler et al., Phys. Rev. A, 74, (2006) 24 Mg + + C 60 (~14 K) It may not be possible to find closed optical pumping cycles to laser cool molecules. Sympathetic cooling has been extensively used to spatially confine molecules making possible to perform many molecular physics experiments.

Chemistry and Ion Traps Future: High resolution spectroscopy State selective studies of chemical reactions Prepare molecules in specific internal quantum state Coherent manipulation of internal and external degrees of freedom Use molecular internal degrees of freedom in an ensemble to perform logic operations (quantum computation processes). More recently: S. Willitsch, M.T. Bell, A. D. Gingell, S.R. Procter, and T.P. Softley, Phys. Rev. Lett., 100, (2008) (115 mK) A. Ostendorff et al., Phys. Rev. Lett., 97, (2006)

Doppler (mK) and Sideband Cooling (  K) + + CM  z- : BM  z+ : To achieve Doppler limit, minimize micromotion using DC bias on rods to compensate the trap, see: D. J. Berkeland, et al., Journal of Applied Physics, 83, 5025 (1998) Hence, potential energy of two ions Coulomb crystal: At T D the expected quantum of vibrational motion, Cooling beyond Doppler limit Raman type transitions to cool crystal to

Ion trap D. J. Berkeland, Review of Scientific Instruments, 73, 2856 (2002) R = 0.5 mm 2Z 0 = 6 mm U 0 ~100 V V rf ~ V  rf = MHz U 1, U 2, U 3, U 4 ~-100 mV Stainless Steel Macor Polyimide

Ion trap McMaster-Carr GTRI Machine shop Kimball Physics

Ca oven e-gun z y x leak valve Ion trap

Ca + Laser system Ions loaded by optically selected photoionization of neutral 40 Ca: 1 S 0 – 1 P 1 : 423nm (TOPTICA) 1 P 1 – above threshold: 375 nm (NICHIA) 40 Ca + D 3/2 S 1/2 P 1/2 Doppler Cooling 397 nm (7.7 ns) (1.08 s) (94.3 ns) High Power Frequency Doubled Tunable Diode Laser: 397nm tunable diode laser tapered amp. AOM SHG 866 nm Grating Stabilized Diode Laser: 866 nm All lasers used to cool 40 Ca + are commercially available (TOPTICA) 1S01S0 1P11P1 423 nm 40 Ca 375 nm

Ca + Laser system D 3/2 397 nm 866 nm S 1/2 P 1/2 40 Ca + Sideband Cooling Grating Stabilized Diode Laser: 854 nm Diode laser system narrowed by fast electronics: 729 nm Home made Fabry-Perot cavity to lock laser frequency Finesse ~200 Linewidth ~15KHz grating stabilized diode laser 729 nm (1.045 s) D 5/2 P 3/2 854 nm (101 ns) (7.4 ns) AOM Invar cavity

729 nm (1.045 s) D 5/2 P 3/2 854 nm (101 ns) (7.4 ns) Ca + Laser system D 3/2 S 1/2 P 1/2 40 Ca + Sideband Cooling Grating Stabilized Diode Laser: 854 nm Diode laser system narrowed by fast electronics: 729 nm ULE temperature stabilized high finesse cavity in vacuum Finesse > 100K grating stabilized diode laser AOM

Ion Trap Table Lens system M = 5.4x Vacuum chamber at 5.5x torr Magnetic field: 3-6 G along x-axis RF amplitude ~ V at MHz z y x z y x Helmholtz coil 866 & 854 nm 397 nm 423 nm 729 nm leak valve ion pump CCD camera PMT helical resonator

Doppler Cooling 40 Ca + D 3/2 397 nm 866 nm S 1/2 P 1/2 40 Ca + T D ~ 570  K 160  m  rf =14.13 MHz V rf = 134 V U 0 = 95 V I 397 = 230  W I 866 = 550  W Compensation voltages: U 1 = -100 mV U 2 = -100 mV U 3 = -320 mV U 4 = -135 mV  = 22 MHz 80  m

Reaction of O 2 with 40 Ca + at mK Load two 40 Ca + ions 71  m 59  m D 3/2 397 nm 866 nm S 1/2 P 1/2 40 Ca + Tickle U 3 rod: mV pp to measure radial secular frequency,  r /2  amu x 1216 kHz kHz m = = 56.2 amu CaO + Open leak valve, pressure 5x10 -9 torr Wait ~ 5 min.

Ions are separated by 27.2  m. Expected axial secular frequency:  z1 = 115 KHz M. Drewsen, et al. PRL, 93, (2004) CM  z- = 104 KHz BM  z+ = 185 KHz 40 Ca Ca 16 O + D 3/2 397 nm 866 nm S 1/2 P 1/2 40 Ca + Tickle 2 of the U 0 end caps: 4-6 V pp to measure axial secular frequency,  z /2  Reaction of O 2 with 40 Ca + at mK 40 Ca Ca 16 O + 71  m 59  m 40 Ca Ca +  z- = 104 KHz  z1 = 115 KHz

Sideband Cooling Spin Polarization (Optical Pumping Zeeman levels) m = 1/2 S 1/2 m = -1/2 m = -3/2 m = -5/2 D 5/2 P 3/2 m = -1/2 m = -3/2 729 nm 854 nm Remove quanta of vibration (Anti-Stokes transition on two-ions system) 729 nm 854 nm n n -1 S 1/2 m = -1/2 n -1 n Ca + -Ca +  z1 = 115 KHz Ca + -CaO +  z- = 104 KHz P 3/2 m = -3/2 D 5/2 m = -5/2 Zeeman components ~25 MHz (B = 3G) m’ = -1/2 m = 3/2 m’ = -1/2 m = -5/2 S 1/2 D 5/2  z ~100 kHz  rf =14.13 MHz 729 frequency

Sideband Cooling and Temperature Measurement D 3/2 S 1/2 P 1/2 729 nm D 5/2 P 3/2 397 nm 866 nm 854 nm Cycle repeated 100 times for each  729 (10 KHz/step). Optimum time pulse widths from Rabi oscillations  Rabi ~ 50 KHz   t Zl,  t sb ~  s DDS boards RF amps, FPGA, attenuators

Sideband Cooling and Temperature Measurement D 3/2 S 1/2 P 1/2 88 Sr nm D 5/2 P 3/2 422 nm 1092 nm 1033 nm J. Labaziewicz, et al. PRL, 100, (2008) Heating rates in cryogenic surface-electrode ion traps using 88 Sr +

Conclusions 80  m We have built a linear Paul trap to perform single ion/molecule reactions at low temperatures (< mK) Single 40 Ca + ions are laser cooled close to Doppler limit ( T D ~ 570  K) Laser excitation schemes to cool the 40 Ca Ca 16 O + crystal to its vibrational ground state (T < 100  K) We observe the product of the reaction of O 2 with single 40 Ca + ions at mK by measuring vibrational excitation frequencies of the atom-molecule crystal

Acknowledgments Professor Kenneth Brown Dr. Richart Slusher Director of GT-Quantum Institute GTRI Machine Shop Start-up funds Ion trap construction & vacuum: James Goeders Electronics: Yatis Dodia, Grahame Vittorini, Claire Tornow, Jamie Hodges High finesse cavity: Grahame Vittorini, James Goeders 729 lock: Ken Wright Lasers & optics: Claire Tornow, Craig Clark Data acquisition: Craig Clark 12 Dec. 2007