x=47.19 mm
Towards a Strontium Optical Lattice Clock
N. Poli, A. Alberti, R. Drullinger, G. Ferrari, V. Ivanov, M. Prevedelli, M. Schioppo, F. Sorrentino, G.M. Tino
LENS and Department of Physics, Istituto Nazionale Fisica Nucleare, Istituto Nazionale
Fisica della Materia - CNR, Polo scientifico - University of Florence, 50019 Sesto Fiorentino, Italy
www.lens.unifi.it/tinogroup/Sr/
Abstract
Strontium atom
We report on our progress toward the realization of an optical frequency
standard referenced to strontium intercombination lines. While first
frequency measurement of the weakly allowed 1S0 - 3P1 transition was done
with saturation spectroscopy on a thermal beam, we are preparing the
experimental setup for high resolution spectroscopy on ultracold atoms of
the doubly-forbidden 1S0 - 3P0 line. Our current setup allows the capture
more than 107 atoms at 1 mK in 500 ms in two stages of magneto-optical
trapping. We also demonstrated the dipole trapping of ultracold strontium
isotopes for accurate spectroscopy and collisional measurements. For high
resolution spectroscopy of doubly forbidden transition we have also
prepared a 698 nm ‘clock’ laser stabilized on high finesse symmetrically
suspended cavity and an high power 813 nm light source for the optical
lattice trap at the ‘magic’ wavelength.
- Optical clock using narrow
intercombination transitions
0-1
7p 1P 1
1
6p P 1
1
fast all-optical cooling
dipole trapping
degenerate Fermi & Bose gases
6 s S0
293 nm
110 kHz
TD
t
Isat
460.86
1 mK
770 mK
5 ns
42mW/cm2
689.45
460 nK
180 nK
20 ms
3 mW/cm2
717nm
25MHz
6p 3P J
5p P 1
4d 1D 2
amax
(m/s2)
495 103
78
3
2
1
497 nm
2.3 MHz
1.8mm
450Hz
2
1
0
671nm-4
1.5 10 Hz
- Inertial sensors for measurements at micrometer scale
5d 3D J
707nm
679nm
1
2
1
0
6 s 3S 0
6.5mm
620Hz
461nm
461
32 MHz
3
4d D J
3
2
1
3
5p P J
698 nm87
1 mHz ( Sr)
1
S
Sr Isotope
Natural
Abundance
88
Nuclear Spin
I
0
87
9/2
7,0 %
86
0
9,8 %
84
0
0,56 %
82,6 %
689 nm
7.6 kHz
5 s 2 1S 0
Spectroscopy on ultranarrow Sr transition
Tr
257 nm
240 kHz
0-0
0-2
- Physics of ultracold atoms
l(nm)
1
P
1
D
3
3
S
P
3
D
Optical lattice clock
88
Sr-86Sr 1S0-3P1 intercombination lines
- Trapping neutral atoms at “magic” wavelenght for 1S03
P0 transition
(compensation of AC Stark Shift effect on ground and
excited state)
- Spectroscopy in Lamb-Dicke regime (no mechanical
effect of the interrogating light on the atoms, Doppler,
recoil effect, ... )
M. Takamoto et al., Nature 435, 321-324 (2005)
Servo1
Detector
~
ECDL
OI
AOM1
PZT
OI
EOM
RC
QWP
AOM2
Slave
OI
GPS referenced
oscillator
AOM3
-
Sr - 86Sr isotope shift measurement : 163 817.4 (0.2) kHz [1]
- Negligible effect due to higher order polarizability for 87Sr
doubly forbidden transition (<10-18)
88
Servo2
Atomic beam
spectroscopy
Frequency
comb
:
434 829 121 311 (10) kHz [1]
- Absolute frequency of 88Sr intercombination
line
-11
(relative accuracy 2*10 )
A.Brusch et al., Phys. Rev. Lett. 96, 103003 (2006)
86
- Absolute frequency of Sr intercombination line: 434 828 957 494 (10) kHz [1].
G. Ferrari et al., Phys. Rev. Lett. 91, 243002 (2003)
88
Sr-87Sr 1S0-3P0 doubly-forbidden transitions
Compact high power 813 nm laser
Spectrosocopy on ultra-narrow 1S0-3P0
intercombination transitions
- multiple ground state sublevels
- large sensitivity to magnetic fields (MHz/T)
and lattice polarization (Hz/rad)
Odd isotope (87Sr)
- mHz natural linewidth transitions (hyperfine
coupling, I=9/2)
- direct spectroscopy
- non-degenerate ground state
- small magnetic field dependency
- already demonstrated on Yb
- Master oscillator (ECDL) + tapered
amplifier
- 600 mW single mode (813 nm)
- 1D optical lattice at magic wavelength
Even isotopes (88Sr, ...)
- doubly forbidden (no hyperfine coupling, I=0)
- new spectroscopy schemes (magnetic fieldinduced spectroscopy, EIT, four-wave mixing, ..)
ECDL
PMF
to atoms
Optical lattice clock goals
- frequency stability sy(t) ~ 10-16 t-1/2
- accuracy ~ 10-17 -10-18
OI
AOM
OI
P = 600 mW
w0 = 30mm
MOPA
U0 = 30 mK
G = 0.6 s-1
106
N=
t=5s
- 50% of output power coupled into the fiber
- laser source mounted on a 50 cm * 50 cm
optical breadboard
A. V. Taichenachev et al., Phys. Rev. Lett. 96, 083001 (2006)
Clock laser
Horizontally symmetric suspended cavities
Laser prestabilization
The lasers to excite the forbiddentransitions are
spectrally narrowed by phase and frequency
stabilization onto passively isolated and high
finess opticalcavities
- Pound-Drever-Halllocking (~3 MHz BW)
The reference cavity
- ULE spacer (~ 10-9/K) (l. = 10 cm, f =10 cm)
- SiO2 mirror (T ~ 3 ppm, finesse ~ 5 105)
- horizontal symmetric mount (frequency response to
accelerations ~ 15 mHz/mg)
689 nm laser source (1S0 - 3P1 transition Dn ~ 7 kHz)
FEM simulations
Spectral noise density (Hz2/Hz)
- Simulation of cavity length changes and mirror tilt due to
mechanical vibrations
laser unlocked
cavity lock
cavity lock (damping on)
atomic signal lock (<5 Hz bw)
10
10
109
108
107
106
105
104
103
102
101
100
10-1
10-2 -1
10
- Frequency noise spectra measured
with a resonance mode of a second
independent cavity.
- Optimized geometry for the cavity suspension (T. Rosenband,
J. Bergquist)
- Laser linewidth (Dn ~ 20 Hz)
100
101
102
103
104
105
Frequency (Hz)
698 nm laser source (1S0 - 3P0 transition Dn < 1 mHz)
Two step stabilization of698 nm ECDL on high finesse
cavities
- first step stabilizationon 104 finesse tunablecavity (Dn <
1 kHz)
- second step stabilization on high finesse symmetrically
suspended optical cavity (Dn < 1 kHz)
Cooling and trapping Strontium atoms
oven
Measuring cavity sensitivity to vibrations
-Measurement performed with two identical cavities placed on
independent tables. First cavity used to pre-stabilize the laser,
while the second is used as a test cavity.
Blue MOT (1S0-1P1- 461 nm)
- 100 ms capture
- 5 ms blue molasses
About 2*108 88Sr atoms
at 2 mK - t ~ 100 ms
Transverse
cooling stage
Red MOT (1S0-3P1- 689 nm)
- Broad-band recapture (Dt~ 100 ms)
- Single frequency MOT (Dt~ 10 ms)
r
g
- Sensitivity measured both with single tone shaking
(loudspeaker @ ~500 Hz) and with broadband vibration noise
(noisefloor of the laboratory)
Zeeman slower
7 88
Up to ~10
Sr atoms @ 1 mK
88
Dipole trapping (single isotopes, Sr mixtures)
86
Sr isotopic
Trap region
N. Poli et al. Phys. Rev. A 71, 061403(R) (2005)
- Collisional properties of 88Sr and 86Sr samples and
88
Sr and 86Sr mixture
88
- Production of ultracold Sr samples (r = 0.1)
G. Ferrari et al. Phys. Rev. A 73, 023408 (2006)
Future prospect...
- Optical frequency reference on Sr transitions
- Compact and transportable experimental setup
Financial support
- Optical clocks for Earth and Space applications
ASI CONTRACT 1/013/06/0 (2006)
ESA CONTRACT 19838/06/F/VS (2006)
ESA CONTRACT MAP (2006)