spectroscopy of a forbidden transition in a 4 he bec and a 3 he degenerate fermi gas rob van rooij,...
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Spectroscopy of a forbidden transition in a 4He BEC and a 3He
degenerate Fermi gas
Rob van Rooij, Juliette Simonet*, Maarten Hoogerland**, Roel Rozendaal,
Joe Borbely, Kjeld Eikema, and Wim Vassen
Institute for Lasers, Life and Biophotonics, VU University, Amsterdam
* École Normale Supérieure, Laboratoire Kastler-Brossel, Paris, France ** University of Auckland, Auckland, New Zealand
0
5
10
15
20
eV
Singlet (S=0)Parahelium
Triplet (S=1)Orthohelium
0 1 2 0 1 2Orbital angular momentum
1s
2s
3s
3p2p
3d
2s
3s
3p2p
3d
First excited state: 19.8 eV
Always one 1s electron
No electric-dipole-allowed transitions between singlet and triplet states
He Level Scheme
He+
He Level SchemeLifetimes
2 1S0: 20 ms
2 3S1: 8000 s (He*)
0
20
22
eV
0 1 2 0 1 2Orbital angular momentum
1s
1s2s 1S0
2p
1s2s 3S1 (He*)
2p
He Level SchemeLifetimes
2 1S0: 20 ms
2 3S1: 8000 s (He*)
2 3S1 → laser cooling and trapping
0
20
22
eV
0 1 2 0 1 2Orbital angular momentum
1s
1s2s 1S0
2p
1s2s 3S1 (He*)
2p
He Level SchemeLifetimes
2 1S0: 20 ms
2 3S1: 8000 s (He*)
2 3S1 → laser cooling and trapping
2 3S1 → 2 1S0 (M1): 1557 nm
A21 = 9.1 x 10-7 s-1
Γ = 2π x 8 Hz
QED effects strongest for low-lying S states0
20
22
eV
0 1 2 0 1 2Orbital angular momentum
1s
1s2s 1S0
2p
1s2s 3S1 (He*)
2p
1557nm
He Level SchemeLifetimes
2 1S0: 20 ms
2 3S1: 8000 s (He*)
2 3S1 → laser cooling and trapping
2 3S1 → 2 1S0 (M1): 1557 nm
A21 = 9.1 x 10-7 s-1
Γ = 2π x 8 Hz
QED effects strongest for low-lying S states
2 3S1 can be trapped at 1557nm (23S→23P : 1083 nm)
0
20
22
eV
0 1 2 0 1 2Orbital angular momentum
1s
1s2s 1S0
2p
1s2s 3S1 (He*)
2p
1557nm
He Level SchemeLifetimes
2 1S0: 20 ms
2 3S1: 8000 s (He*)
2 3S1 → laser cooling and trapping
2 3S1 → 2 1S0 (M1): 1557 nm
A21 = 9.1 x 10-7 s-1
Γ = 2π x 8 Hz
QED effects strongest for low-lying S states
2 3S1 can be trapped at 1557nm (23S→23P : 1083 nm)
2 1S0 anti-trapped
0
20
22
eV
0 1 2 0 1 2Orbital angular momentum
1s
1s2s 1S0
2p
1s2s 3S1 (He*)
2p
1557nm
He Level SchemeLifetimes
2 1S0: 20 ms
2 3S1: 8000 s (He*)
2 3S1 → laser cooling and trapping
2 3S1 → 2 1S0 (M1): 1557 nm
A21 = 9.1 x 10-7 s-1
Γ = 2π x 8 Hz
QED effects strongest for low-lying S states
2 3S1 can be trapped at 1557nm (23S→23P : 1083 nm)
2 1S0 anti-trapped
Similar for fermionic isotope 3He
Isotope shift
0
20
22
eV
0 1 2 0 1 2Orbital angular momentum
1s
1s2s 1S0
2p
1s2s 3S1 (He*)
2p
1557nm
Experimental setup
Crossed optical dipole trap at 1557 nm
Bose-Einstein condensate of 4He*
Degenerate Fermi gas of 3He*
Dipole trap laser: 40 MHz detuned from
atomic transition
Experimental setup
Crossed optical dipole trap at 1557 nm
Bose-Einstein condensate of 4He*
Degenerate Fermi gas of 3He*
Absorption imaging
Dipole trap laser: 40 MHz detuned from
atomic transition
Experimental setup
Crossed optical dipole trap at 1557 nm
Bose-Einstein condensate of 4He*
Degenerate Fermi gas of 3He*
Absorption imaging
Dipole trap laser: 40 MHz detuned from
atomic transition
160
170
180
190
200
210Time of Flight
(ms)
MC
P S
ignal (a
.u.)
TOF on Micro-channel Plate (MCP)
Experimental setup
Crossed optical dipole trap at 1557 nm
Bose-Einstein condensate of 4He*
Degenerate Fermi gas of 3He* 160
170
180
190
200
210Time of Flight
(ms)
MC
P S
ignal (a
.u.)
TOF on Micro-channel Plate (MCP)
Absorption imaging
f spec .=f combmode+f beat+f AOM
Dipole trap laser: 40 MHz detuned from
atomic transition
Mode-locked erbium doped fiber laser (Menlo Systems)Referenced to a GPS-controlled Rubidium clock
Load a 4He BEC or 3He DFG from magnetic trap into optical dipole trap
Apply spectroscopy beam
Measurement sequence
Load a 4He BEC or 3He DFG from magnetic trap into optical dipole trap
Apply spectroscopy beam Turn off the trap and record MCP
signal Determine remaining atom number
Measurement sequence
160 170 180 190 200 210Time of Flight (ms)
MC
P S
ignal (a
.u.)
Load a 4He BEC or 3He DFG from magnetic trap into optical dipole trap
Apply spectroscopy beam Turn off the trap and record MCP
signal Determine remaining atom number Increment laser frequency via
Measurement sequence
f beat
FWHM: 90 kHz
60 60.1 60.2 60.3 60.4Beat frequency (MHz)
12010080
60
40
20
0
Rem
ain
ing a
tom
s (%)
160 170 180 190 200 210Time of Flight (ms)
MC
P S
ignal (a
.u.)
Systematics
Recoil shift, 20 kHz Mean field, < exp. uncertainty
ℏ k
p
Systematics
Recoil shift, 20 kHz Mean field, < exp. uncertainty Zeeman shift
ℏ k
p
2 3S1
MJ=+1MJ= 0
MJ=-1
MJ=+1
MJ=0
MJ=-1
fR FEnerg
y
0
B-field
Systematics
Recoil shift, 20 kHz Mean field, < exp. uncertainty Zeeman shift AC Stark shift:
Measure for various powers
Extrapolate to zero power
ℏ k
p
2 3S1
MJ=+1MJ= 0
MJ=-1
MJ=+1
MJ=0
MJ=-1
fR FEnerg
y
0
B-field
AC Stark shift 4He
Accounted for:– Recoil shift (20.1 kHz)– Mean field– Zeeman shift
192 510 702.150 4 (41) MHz
Relative uncertainty: 3 x 10-11
Preliminary result
Quantum statistical effect
4He* BEC
occupy ground state
fluctuating atom number
Quantum statistical effect
4He* BEC
occupy ground state
fluctuating atom number
3He*, low power
atoms fill up the trap
constant atom number
Quantum statistical effect
4He* BEC
occupy ground state
fluctuating atom number
3He*, low power
atoms fill up the trap
constant atom number
3He*, P > 300 mW
Trap depth large enough to accommodate full thermal distribution
Measured AC-Stark shift curve non-linear
100
200
300
400
500
600Power
(mW)
0.2
Fit T
em
pera
ture
(u
K)
0.6
0.4
AC Stark shift 3He
Accounted for:– Recoil shift (26.7 kHz)– Mean field– Zeeman shift
192 504 914.431 7 (14) MHz
Relative uncertainty: 8 x 10-12
Preliminary result
Results
Drake
Pachucki
Indirect expt.
Our result
f – 192510700 (MHz)
Helium 4 transition frequency
Results
Drake
Pachucki
Indirect expt.
Our result
f – 192510700 (MHz)
Helium 4 transition frequency
f – 192502660 (MHz)
Drake
Pachucki
Our result
Indirect expt.
Helium 3 transition frequency
Results
Drake
Pachucki
Indirect expt.
Our result
f – 192510700 (MHz)
Helium 4 transition frequency
f – 192502660 (MHz)
Drake
Pachucki
Our result
Indirect expt.
Helium 3 transition frequency
f – 8034 (MHz)
Drake
Pachucki
Our result
Isotope shift In isotope shift calculations
many terms cancel, reducing the theoretical uncertainty
Theoretical uncertainty dominated by nuclear charge radii determined from electron-nucleus scattering experiments
Summary
First time:
spectroscopy on ultracold trapped 4He* and 3He*
direct measurement between triplet and singlet states in He
observation of the 1557nm 2 3S → 2 1S transition
Observed quantum statistical effects in the dipole trap
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