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Thulium atom for optical lattice clock applications. N. Kolachevsky. D. Sukachev E. Kalganova G.Vishnyakova S. Fedorov V. Sorokin. P.N. Lebedev Physical Institute National Metrology Institute VNIIFTRI Moscow Institute of Physics and Technology. Thulium Project.

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thulium atom for optical lattice clock applications
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

slide2

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

slide3

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
slide5

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
slide6

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)

slide7

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)

slide8

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)

slide9

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

slide10

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?

slide12

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

slide14

Oven

(1100 K)

Zeeman slower

MOT chamber

slide17

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

temperature measurements
Temperature measurements

5

time, ms

0

Ballistic expansion of the atomic cloudto measure temperature

temperature in tm mot
Temperature in Tm MOT

TD = 240 K

Temperature mK

Tmin = 25 K

Temperature mK

Detuning d

Saturation parameter

magnetic field
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

magnetic trap for tm

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

second stage cooling
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

second stage cooling1
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)
slide26

Clock lasers at Lebedev Institute

Ultra stable cavitites

Instability~ 10-15 (1-100 s)

Finesse (~200000)

slide27

Stabilized laser system

Second stage cooling: 1.06 mm

Clock laser: 1.14 mm

slide28

First observation of clock transition

Clock laser scan @ 1.14 mm

Cloud spectroscopy T= 100 mK

Signal

slide29

Clock transition linewidth

FWHM(P0) = 0.5 MHz

Doppler broadening

at100 mK

Optical lattice needed!

(Lamb-Dicke regime)

optical trapping
Optical trapping

Red detuning

Blue detuning

slide31

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

slide32

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
slide33

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