Laser Cooling of Thulium Atomspower1.pc.uec.ac.jp/~toru/AEP/kolachevsky/notes/Tm_UEC.pdf · Laser...
Transcript of Laser Cooling of Thulium Atomspower1.pc.uec.ac.jp/~toru/AEP/kolachevsky/notes/Tm_UEC.pdf · Laser...
Laser Cooling
of Thulium Atoms
P.N. Lebedev Physical Institute
Moscow Institute of Physics and Technology
Russian Quantum Center
N. Kolachevsky
D. Sukachev
E. Kalganova
G.Vishnyakova
A. Sokolov
A. Akimov
V. Sorokin
optical atomic clocks – a new era
of clocks
Laboratory frequency measurements
10-9
10- 01
10- 11
10- 21
10- 31
10- 41
10-15
10-16
1950 1960 year
rela
tive u
ncert
ain
ty
1970
Cs fountain
Cs beam
Re-definition of the second
1980 1990 2000 2010
Cs Essen
iodine stabilized He-Nelaser
H
Ca
H
HYb
+Hg
+
Sr+
SrHg
+
Hg+ vs Al
+
Al+ vs Al
+
Sr
10-17
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.
• strong rate > 107 s-1
• cycled
• accessible for laser sources with a power of > 1 mW
Requirements for an efficient laser cooling transition:
Редкоземельные элементы(группа лнтаноидов)
Very recently a significant progress in laser cooling and
trapping of some lanthanides, including hollow-shell
ones, is achieved. They are intensively studied and
successfully implemented in
• precision spectroscopy and optical frequency
metrology
• study of interactions in quantum regime, study of
quantum gases
Applications
Ytterbium optical lattice clock are
unprecedentedly stable
N. Hinkley at al., arXiv:1305.5869v1
Comparison of two identical
Yb clocks is performed at
NIST, 2013 in the group of
Andrew Ludlow
Magnetic gases
Cr:
dipole-dipole
interactions
T. Lahaye,et al., Phys Rev Lett.
080401 (2008)
Optical
lattice+microscope for
degenerate gases?
W. S. Bakr, J. I. Gillen, A. Peng, S.
Foelling, M. Greiner
Nature 462, 74-77 (2009)
Rb
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.
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)
Feshbach resonance in Er
134 f 26sTm:
shell s p d f
L 0 1 2 3
- one vacancy in the 4 f shell
- relatively simple level structure
- fine splitting of the ground state
3
1 2
L
S
Large J causes large magnetic moments of the ground state
Thulium electronic structure
4ground Bm m
7 / 2J
5/ 2J
Similar polarizabilities of the ground-state fine structure components
To what extent the transition frequency remains
unperturbed? Calculations needed!
(V.D. Ovsyannikov, 2010 )
Optical
lattice
L S
L S
M1 transition = 1.14 mm, ~ 1 Hz
2f Ry
Shielding of the 4f shell levels
26s4 nf
collisions
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)
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)
5410in el -
He
Tm
The M1 transition in Tm atom
Spectroscopy on the ground state sublevels in lanthanides
is not yet performed
Thulium: = 1.14 mm, ~ 1 Hz
- suppression of the external electric fields perturbations
- small black-body shift
- loading in the optical lattice with small perturbation of
the clock transition
- strong -dependency 2f Ry
Laser cooling of Thulium
13 24 6f s 7/ 2J
13 24 6f s 5/ 2J
M1
transition
5d , =9/26s J
5d , =7/26s J
5d , =11/26s J
5d , =9/26s J
5d , =7/25/26s2
J
6s26p , =11/21/2 J
2 9413 cm-1
2 8733 cm-1
22560 cm-1
23335 cm-1
22468 cm-1
22420 cm-1
{
decay9/ 2J
410 nm17ns
Cooling
transitions
13 2
3/24 5 6f d s
Cooling transitions in Tm
531 nm440 ns1.14 mm
12 2
5/ 24 5 6f d s
Oven
(1100 K)
Zeeman slower
MOT
chamber
temperature Co
vap
or
pre
ssure
, m
bar
melt
boil
Zeeman slowing
slower
2D molasses
oven
410 nm
initial beam ~ 10 at/s9
slowing 1% atoms
beam size 1 cm2
flux (typ) 10 at/s cm7 2
~v4
0 200 400 600 800
0
2
4
6
co
unts
[10
]6 s
-1
velocity [m/s]
4 - 5
3 4-
beam 45
Dopplerprofilewithoutslowing
slowedatoms25 m/s
Slower operation
Oven design
Magneto-optical trap (2010)
106 atoms Tm-169
t, seconds
310 cm
3(2) 10s
-
The life time of Tm atoms
in the MOT
Binary collisions in the MOT
“Dark” MOT implemented
Temperature of atoms
0 1 2 3 4 5
0
1
2
3
4
0.5 red detuning
0.40.0
I0 [mW/cm ]2
dec
ay r
ate
[s
]t
-1-1
28 s-1
24 s-1
G 18 1 s-1
G0 [ s-1
]
0.5
1.0
1.5
G1= 22(6) s-1
5 times more atoms
Temperature measurements
time, ms0 5
Ballistic expansion of the atomic cloud
to measure temperature
Temperature in Tm MOT
IT
F
IT
F
min
240
25DT K
T K
m
m
Detuning
Tem
per
atu
re m
K
Saturation parameterT
emp
erat
ure
m
K
Tmin = 25 mK
TD = 240 мкК
Magnetic field
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
Doppler:
sub-Doppler
BD e
B
kgv
m
BS g
B
kgv
m
Role of Landé g-factors
Rb: gg = 1/2, ge = 2/3
M. Walhout, J. Dalibard, S.L.Rolston, and W.D. Phillips, J. Opt.Soc. Am. 9, 1997 (1992)
Tm: gg = 1.14, ge = 1.12
(2% difference) (30% difference)
Magnetic trap for Tm
MOT
B = 0
MT
B ≠ 0
20 G/cm
t, ms0 5 10
t, ms10 30 500100 30020
40 000 atoms,
life time 0.5-1s,
T~ 40 mK
Magnetic trap(in presence of gravitation)
IF = 4
B
U
z
effectivepotential
m F = 4
m F = 4
I
E Bm -
z
Magnetic trap(in presence of gravitation)
IF = 4
B
U
z
effectivepotential
m F = 2
m F = 2
I
E Bm -
z
Magnetic trap profile
density [arb. un.]
0 50 100 150 200 2500
1
2
3
4
5
Ver
tica
l co
ord
inate
, m
m
g
Only atoms in mF=+2,3,4 states are trapped
time, ms
0 200 400 600 800 1000
tem
per
atu
re,
Km
0
20
10
30
40
50
60
Temperature
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 cooling
Second stage cooling
0 1 2 3 4 5 6 7 ms
• 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)
0 2 4 6 8 10 1230
40
50
60
70
red detuning,
0
tem
pe
ratu
re,
Km
Optical trapping
MOT
mirror
trapping
laser
w0=30 mm
Red detuning Blue detuning
Spectroscopy of Tm clock transition in
the optical lattice
Dipole optical trap with a
standing wave
Excitation of the clock
transition in trapped atoms
One trapping beam
Optical lattice
530.660 nm
532.0 nm
13 24 6f s 7/ 2J
530.7 nm
12 2
5/ 24 5 6f d s
trapping
• 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
13 24 6f s 7/ 2J
530.7 nm
12 2
5/ 24 5 6f d s
trapping
• 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!
Intermediate conclusions
- 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
Stabilized laser systems at Lebedev Institute
1 10
10-14
100 1000averaging time [s]
Alla
n d
evia
tion
10-13
Vertical cavity F=60000
Comparison of two systems
designed for 698 nm
Laser systems for optical clocks at Lebedev
InstituteTransportable setup
Vertical cavity
Compensation of temperature fluctuations
9 210 ( )cl l T T - -
ULE thermal expansion coefficient
8 10 12 14 16 18 20 22 24
50
55
60
65
70
75
80
Температура [ C]o
Tc
Частота
сигнала биений
МГц
[]
Изм
енение
длины
резонатора
нм
[]
0
5
10
15
45
Temperature [oC]
Be
atn
ote
fre
qu
en
cy M
Hz]
Ca
vity le
ng
th v
aria
tio
n [n
m]
Spectral line width
Fourier frequency [Hz]
Sp
ectr
al p
ow
er
density [arb
. un.]
0.5 Hz
Beatnote between two independent cavities(972 nm, for hydrogen spectroscopy)
J. Alnis, A. Matveev, N. Kolachevsky, Th. Udem, and T. W. Hänsch, Phys. Rev. A 77, 053809 (2008)
GaN diode lasers @ 410.6 nm
Diode PHR-803T
(HD-DVD, Blue-Ray)
+70 oC
Injection locking gives up to 150 mW @ 410.6 nm
Shuji Nakamura
Fraction of power in a single
frequency >95%
Saturation absorption signal in Tm
time [s]
Sig
nal
Tm cloud trapped by
diode laser radiation
slower
2D molasses
oven
410 nm
2D molasses for Tm beam collimation
• Slave diode SF-BW512P
• Max power 500 mW
• Central wavelength:
405 nm @ 25°C
410 nm @ 70°C
• Seed power < 1 mW
• Output power 120 mW
Power in 2D molasses, mW
nu
mb
er
of
ato
ms,
arb
.un
.
up to threefoldincrease in thenumber of atomsin the MOT
Thank you for attention!
Cooling transitions in Tm