Experiments with ultracold RbCs molecules

1. Experiments with ultracold RbCs molecules Cs Rb Peter Molony

2. The RbCs team: Peter Molony, Phil Gregory, Michael Koeppinger, ZhonghuaJi, Bo Lu and Simon Cornish (PI) Theory: Caroline Blackley, Ruth Le Sueur, Jeremy Hutson

3. Goal: A quantum array of polar molecules Caesium Rubidium Mott Insulator Transition Convert to ground state RbCs molecules RbCs: Stable against reactive collisions d = 1.25 D, Brot = 0.5 GHz Induced deff = d /3 for E = Brot /d = 0.8 kV/cm Jakschet al., PRL 89, 040402 (2002) Damskiet al. PRL 90, 110401 (2003)

4. RF The experiment Evaporation in quadrupole trap Load quadrupole trap Atoms collected in MOT Dipole trap loaded by reducing field gradient Reduce the beam intensity to lower the trap depth Levitated dipole trap 2-species BEC! Phys. Rev. A 87 013625 (2013) Apply a magnetic gradient to tilt the trap

5. Atomic State Potential Energy Convert atoms Molecular to molecules Bound State Magnetic Field (B) The experiment • Create a high phase space density atomic sample. 2. Associate weakly-bound molecules via a Feshbach resonance. Magneto-association 3. Transfer Feshbach molecules to the rovibrational ground state using stimulated Raman adiabatic passage (STIRAP). Stimulated Raman Adiabatic Passage (1)3P ~1560nm Free Atoms Feshbach Molecule a3S+ 6S1/2 ~980nm X1S+ Deeply Bound Molecule

6. 87RbCs trapping Cs Rb Phys. Rev. A 89 033604 (2014) ~4000 optically trapped molecules

7.   1 2 87RbCs STIRAP P S P S   3 Relative linewidth of the two lasers D L.P. Yatsenkoet al., PRA 65, 043409 (2002)

8. 87RbCs STIRAP High intensity Intensity control Narrow linewidth L.P. Yatsenkoet al., PRA 65, 043409 (2002)

9. 87RbCs spectroscopy Find suitable intermediate state Excited state with mixed singlet – triplet character Good Franck–Condon overlap for both transitions Our laser: 6330 → 6711 cm-1 Figure: M. Debatin, PhD Thesis, Innsbruck (2013) Data: S. Kotochigova and E. Tiesinga, J. Chem. Phys. 123, 174304 (2005) O. Docenkoet al., PRA 81, 042511 (2010) STIRAP: W.C. Stwalley, EPJD 31, 221-225 (2004)

10. 1556 nm DL Pro EOM 87RbCs STIRAP optical setup Wavemeter Molecules Cavity EOM 980 nm 1556 nm Fibre Coupler l/2 Waveplate l/4 Waveplate Optical Isolator Polarising Beam Splitter Glan-Thompson Polariser AOM Shutter Dichroic Mirror Photo Diode Experiment 980 nm Experiment Cavity 980 nm DL Pro EOM 1556 nm

11. 87RbCs STIRAP optical setup

12. 87RbCs spectroscopy 7 transitions found so far: v’=38 J’=3 192560.47(2) GHz v’=38 J’=1 192556.62(2) v’=37 J’=1 191827.53(2) v’=35 J’=1 190789.15(2) v’=29 J’=3 192577.55(2) v’=29 J’=2 192574.54(2) v’=29 J’=1192572.09(2)

13. Ground state spectroscopy

14. Ground state rotational constant Brot= 0.016352(1) cm-1= 490.23(4) MHz Theory = 0.016(3) J PhysChem A 116,11101 (2012) v=1 state 50 cm-1 higher

15. Outlook Summary • 4000 87RbCs molecules in optical dipole trap. • Magnetic moment of 87RbCs in different internal states measured. • Spectroscopy on electronically excited states. • Absolute ground state found by spectroscopy. • Setup ready for STIRAP. Cs Rb

16. Outlook Outlook • Measure dipole moment of ground state 87RbCs molecules (electrodes ready) • Transfer molecules into absolute ground state (STIRAP) • Produce 85RbCs molecules in new dipole trap • New experimental setup Phys. Rev. A 87 010703(R) (2013)

17. Goal: A quantum array of polar molecules Caesium Rubidium U12 < (U11 + U22)/2 U12 > (U11 + U22)/2 Immiscible Miscible Mott Insulator Transition Convert to ground state RbCs molecules RbCs: Stable against reactive collisions d = 1.25 D, Brot = 0.5 GHz Induced deff = d /3 for E = Brot /d = 0.8 kV/cm Jakschet al., PRL 89, 040402 (2002) Damskiet al. PRL 90, 110401 (2003)

18. Last time Cs2 Feshbach molecules

19. Last time

20. Last time

21. Last time

22. Last time

23. Magnetic moment

24. Magnetic moment

25. Trapped Cs2 molecules

26. 87RbCs Feshbach molecules

27. 87RbCs Feshbach Molecules Cs Rb ~5000 RbCs molecules

28. RbCs molecules • Magnetic moment measurement • Keep molecules in the same position since the magnetic moment • changes while the molecules are falling • Vary magnetic field gradient • Measure position after different period of time mmol,181G = -0.84(1) mB

29. 87RbCs magnetic moment

30. Next step RbCs excited state spectroscopy Excited state potential through Fourier transform spectroscopy (FTS) (O. Docenkoet al., PRA 81, 042511 (2010)) Ground state potential measured using laser-induced fluorescence combined with Fourier transform spectroscopy (LIF-FTS) (C.E. Fellows et al., J. Mol. Spectrosc. 197, 19 (1999))

31. Next step RbCs excited state spectroscopy Resonances at ~ 1556 nm DFWHM ~ 2p x 5 MHz M. Debatinet al., Phys. Chem. Chem. Phys. 13, 18926 (2011)

32. First identify a suitable intermediate state with sufficient oscillator strength with both connected levels Excited state potential from PRA 81, 042511 (2010) Ground state potential from J. Mol. Spectrosc. 197, 19 (1999) • Single photon excited state spectroscopy: • Irradiate molecules only with L1 for 10 ms to 10 ms • Gamma can be calculated detuning the laser • Rabi frequencies can be calculated using the decay during irradiation • Two photon dark state resonance spectroscopy: • Simultaneous irradiation with rectangular light pulses of L1 and L2 • 10 – 100 ms irradiation time • WL2 << WL1 (more 980 nm light) • Vary detuning of L1 (1550 nm) and keep L2 in resonance How do I know DL2 = 0 ???