spectroscopy of a forbidden transition in a 4 he bec and a 3 he degenerate fermi gas rob van rooij,...

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


1s

1s2s 1S0

2p

1s2s 3S1 (He*)

2p


2 1S0: 20 ms

2 3S1: 8000 s (He*)

2 3S1 → laser cooling and trapping

0

20

22

eV


1s

1s2s 1S0

2p

1s2s 3S1 (He*)

2p


2 1S0: 20 ms

2 3S1: 8000 s (He*)


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


1s

1s2s 1S0

2p

1s2s 3S1 (He*)

2p

1557nm


2 1S0: 20 ms

2 3S1: 8000 s (He*)


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


1s

1s2s 1S0

2p

1s2s 3S1 (He*)

2p

1557nm


2 1S0: 20 ms

2 3S1: 8000 s (He*)


2 3S1 → 2 1S0 (M1): 1557 nm

A21 = 9.1 x 10-7 s-1

Γ = 2π x 8 Hz



2 1S0 anti-trapped

0

20

22

eV


1s

1s2s 1S0

2p

1s2s 3S1 (He*)

2p

1557nm


2 1S0: 20 ms

2 3S1: 8000 s (He*)


2 3S1 → 2 1S0 (M1): 1557 nm

A21 = 9.1 x 10-7 s-1

Γ = 2π x 8 Hz



2 1S0 anti-trapped

Similar for fermionic isotope 3He

Isotope shift

0

20

22

eV


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




Absorption imaging


atomic transition

Experimental setup




Absorption imaging


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



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


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


Apply spectroscopy beam Turn off the trap and record MCP

signal Determine remaining atom number


160 170 180 190 200 210Time of Flight (ms)

MC

P S

ignal (a

.u.)


Apply spectroscopy beam Turn off the trap and record MCP

signal Determine remaining atom number Increment laser frequency via


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


4He* BEC

occupy ground state


3He*, low power

atoms fill up the trap

constant atom number


4He* BEC

occupy ground state


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)


f – 192502660 (MHz)

Drake

Pachucki

Our result

Indirect expt.


Results

Drake

Pachucki

Indirect expt.

Our result

f – 192510700 (MHz)


f – 192502660 (MHz)

Drake

Pachucki

Our result

Indirect expt.


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

spectroscopy of a forbidden transition in a 4 he bec and a 3 he degenerate fermi gas rob van rooij,...

Documents