Thulium atom for optical lattice clock applications

1. Thulium atom for optical lattice clock applications N. Kolachevsky D. SukachevE. Kalganova G.VishnyakovaS. FedorovV. Sorokin P.N. Lebedev Physical Institute National Metrology Institute VNIIFTRI Moscow Institute of Physics and Technology

2. Thulium Project Using of Thulium atoms as a candidate for optical clocks was first proposed in 1997 by S. Kanorsky (P.N. Lebedev Physical Institute). Laser cooling scheme and the candidate for clock transition at 1.14 mm were suggested. Progress started after 2007 when laser system for a first-stage cooling was developed. We will report on recent progress at P.N. Lebedev Physical Institute

3. Laser cooling of Lanthanides Electronic structure of lanthanides (Yb, Dy, Er, Tm) is similar to alkali-earth elements (Ca, Sr, Mg) due to a closed outer electronic s-shell. Laser cooling of lanthanides is more challenging because of the absence of closed strong cooling transitions. All of strong transitions possess decay channels. Requirements for an efficient laser cooling transition: • strongrate > 107 s-1 • cycled • accessible for laser sources withapowerof > 1 mW

4. Редкоземельные элементы(группа лнтаноидов)

5. Applications • Significant progress in laser cooling and trapping of lanthanides, including hollow-shell ones, is achieved recently. They are intensively studied and successfully implemented in • precision spectroscopy and optical frequency metrology • study of interactions in quantum regime, study of quantum gases

6. Ytterbium optical lattice clock are unprecedentedly stable Comparison of two identical Yb clocks is performed at NIST, 2013 in the group of Andrew Ludlow N. Hinkley at al., Science Vol. 341 no. 6151 pp. 1215-1218 (2013)

7. Magnetic gases Cr: dipole-dipole interactions T. Lahaye,et al., Phys Rev Lett. 080401 (2008) Optical lattice+microscopefor degenerate gases? W. S. Bakr, J. I. Gillen, A. Peng, S. Foelling, M. Greiner Nature 462, 74-77 (2009)

8. Hollow-shell Lanthanides Vacancies in the hollow 4f-shell (e.g. Er, Dy, Tm) provide big magnetic moment in the ground state. Magnetic moment of Dy equals 10 mB, of Er 6mB. Strong dipole-dipole interactions between ground state atoms. Dipole-interacting condensates and quantum simulators. Feshbach resonance in Er M. Lu, N.Q. Burdick, S.H. Youn, and B.L. Lev Phys. Rev. Lett. 107 190401 (2011) K. Aikawa et al. Phys. Rev. Lett. 108 210401 (2012)

9. Thulium electronic structure Tm: • - one vacancy in the 4 f shell • relatively simple level structure • fine splitting of the ground state Large J causes large magnetic moments of the ground state

10. Optical lattice Similar polarizabilities of the ground-state fine structure components M1 transition  =1.14 m, ~ 1 Hz (V.D. Ovsyannikov, 2010 ) To what extent the transition frequency remains unperturbed?

11. Preliminary calculations

12. Shielding of the4fshell levels Because of the closed 6s2 shell, the inner shells are shielded to the external perturbations. The shileding was first demonstrated experimentally by E.B. Alexandrov in 1983 J. Doyle at al. measured for He-Tm collisions (Nature, 2004) For Tm-Tm collisions in specific magnetic state the shielding disappears (PRA, 2010) Tm collisions E.B.Aleksandrov et al., Opt. Spektrosk., 54, 3, (1983) C.I. Hancox et al. Nature 431, 281 (2004) C.B.Connolly et al., Phys. Rev. A 81, 010702 (2010)‏ He

13. Cooling transitions in Tm

14. Oven (1100 K) Zeeman slower MOT chamber

15. Zeeman slowing

16. Magneto-optical trap (2010) 106 atomsTm-169

17. The life time of Tm atoms in the MOT • Binary collisions in the MOT •  “Dark” MOT implemented • Temperature of atoms 1= 22(6) s-1 t, seconds 5 times more atoms

18. Temperature measurements 5 time, ms 0 Ballistic expansion of the atomic cloudto measure temperature

19. Temperature in Tm MOT TD = 240 K Temperature mK Tmin = 25 K Temperature mK Detuning d Saturation parameter

20. Magnetic field Doppler: Due to specific level structure of Tm atom (degeneracy of the Landé g-factors) sub-Doppler mechanism IS EFFICIENT even in the presence of magnetic field sub-Doppler

21. 10 20 30 100 300 500 t, ms Magnetic trap for Tm MOT  B = 0 0 5 10 t, ms • MT • B ≠0 20 G/cm 40 000 atoms, life time 0.5-1s, T~ 40 K

22. Magnetic trap(in presence of gravitation) z

23. Magnetic trap(in presence of gravitation) z

24. Second stage cooling First stage cooling at 410 nm TD=240 mK Second stage cooling at 530.7 nm TD=9 mK Frequency-doubled laser diode radiation is used

25. Second stage cooling • Efficient cooling recapture directly from • Zeeman slower • Number of atoms similar to blue MOT due • to Zeeman slower design • Recapture efficiency from blue MOT 100% • To reach lower temperatures we need to narrow the diode laser line width (lower than 100 kHz)

26. Clock lasers at Lebedev Institute Ultra stable cavitites Instability~ 10-15 (1-100 s) Finesse (~200000)

27. Stabilized laser system Second stage cooling: 1.06 mm Clock laser: 1.14 mm

28. First observation of clock transition Clock laser scan @ 1.14 mm Cloud spectroscopy T= 100 mK Signal

29. Clock transition linewidth FWHM(P0) = 0.5 MHz Doppler broadening at100 mK Optical lattice needed! (Lamb-Dicke regime)

30. Optical trapping Red detuning Blue detuning

31. One trapping beam • Loading from MOT at 100 mK • Laser Verdi G-12 blue detuned! • Optical trap depth 1 mK • Strong blue transitions mainly contribute to the polarizability • About 1% of atoms is recaptured 530.7 nm trapping 530.660 nm Optical lattice • Loading from MOT at 100 mK • Laser Verdi V-8 red detuned! • Optical trap depth 1 mK • Optical trapping is more efficient for red detuning • Trapping depends on polarization => lattice effect! 530.7 nm trapping 532.0 nm

32. CONCLUSIONS and OUTLOOK • Clock transition at 1.14 mmis observed for the first time • - Tm atoms are trapped in an optical lattice and prepared for spectroscopy of clock transition at 1.14 mm • Temperature of atoms is still too high for efficient recapture into the shallow lattice => further cooling is necessary • Narrow line lasers for second stage cooling (530.7 nm) and studying of metrological transition (1.14 mm) • - Increasing of the number of atoms

33. GaN diode lasers @ 410.6 nm DiodePHR-803T (HD-DVD, Blue-Ray) +70 oC Shuji Nakamura Fraction of power in a single frequency >95% Saturation absorption signal in Tm Signal Tm cloud trapped by diode laser radiation time [s] Injection locking gives up to 150 mW @ 410.6 nm

34. Thank you for attention!