Post on 16-Jan-2016
Ultracold 3He and 4He atoms near quantum degeneracy:
QED test and the size of the helion and -particle
Rob van Rooij, Joe Borbely, Juliette Simonet*, Maarten Hoogerland**, Kjeld Eikema, Roel Rozendaal and Wim Vassen
* École Normale Supérieure, Laboratoire Kastler-Brossel, Paris, France ** University of Auckland, Auckland, New Zealand
Outline
• What is quantum electrodynamics (QED)?
• Why use helium spectroscopy to test QED?
• How we tested QED (and also nuclear few-body physics)
What is quantum electrodynamics (QED)?
vacuum is never empty, but filled with virtual particles – appearing suddenly and then quickly disappearing
electron self energy
Dirac
relativity,electron spin
100 GHz
Lamb
10 GHz
QED2n
R
Modern era of QED began with the discovery of the Lamb shift in 1947 (Willis Lamb; hydrogen atom)
BohrEnergyn=1
(13.6 eV = 106 GHz)
1 GHz
proton spin
Hyper-finesplitting
0.01 GHz
proton size
Nuclear effects
2
tE Heisenberg uncertainty principle
vacuum polarization
Vacuum produces electron-positron pairs
A theory that describes how light and matter interactcontributions from empty space (the vacuum)
Shift:
Electrons interact with themselves
Why use helium spectroscopy to test QED?
• Next simplest atom (from a theoretical point of view) after atomic hydrogen• 2-electron atom (get electron-electron interactions)• 3-body system (electron, electron, nucleus)
First excited state: 1s2s 23S1
( n 2S+1LJ )
Ground state: 1s2 11S0
n=1,2,3,…S = s1+s2 , s=±½L = 0,1,2,… (S,P,D…)J = |L-S|,…,|L+S|
E = h x 5 130 494.9(9) GHzPrecision: 175 parts per billion (10-9)
3 years later…E = h x 5 130 495.04(17) GHzPrecision: 34 parts per billion (10-9)
Why use helium spectroscopy to test QED?
• Next simplest atom (from a theoretical point of view) after atomic hydrogen• 2-electron atom (get electron-electron interactions)• 3-body system (electron, electron, nucleus)
E = h x 5 945 204 212(6) MHzPrecision: 1 part per billion (10-9)
Why use helium spectroscopy to test QED?
• Next simplest atom (from a theoretical point of view) after atomic hydrogen• 2-electron atom (get electron-electron interactions)• 3-body system (electron, electron, nucleus)
E = h x 192 510 702 145.6(1.8) kHzPrecision: 8 parts per trillion (10-12)
Lifetimes (He*)
2 1S0: 20 ms , FWHM = 8 Hz
2 3S1: 8000 s
QED effects strongest for low-lying S states
Why use helium spectroscopy to test QED?
• Next simplest atom (from a theoretical point of view) after atomic hydrogen• 2-electron atom (get electron-electron interactions)• 3-body system (electron, electron, nucleus)
E = h x 192 510 702 145.6(1.8) kHzPrecision: 8 parts per trillion (10-12)
Extremely weak transition long interaction time
Modified from E. Eyler Science 333,164 (2011)
Particle accelerators
Sun (surface)
Supernova
Sun (centre)
Room temperature
Interstellar space
1557 nm laser light
1083 nm laser light
MCP
Same laser but different frequency detunings for:• collimation• slowing• cooling• trapping• detection
How we tested QED: Experimental setupEnergy
1s2s 1S0
1557 nm
1s2s 3P2
1s1s 1S0
1s2s 3S1
electron bombardment(20 eV)
1083 nm
1s2s 1S0
1s2s 3S1
1557 nm
1s2s 3P2
1s2s 1P1
1s1s 1S0
2 3S1 can be trapped at 1557 nm(red detuned from 23S1→23P2: 1083 nm)
2 1S0 anti-trapped(blue detuned from 21S0→21P1: 2060 nm)
How we tested QED: Optical trapping
Energy
How we tested QED: Experimental tools
Nobel prize in physics milestones:
• 2001: Eric A. Cornell, Wolfgang Ketterle, Carl E. Wieman achievement of Bose-Einstein condensation
• 2005: Roy J. Glauber, John L. Hall, Theodor W. Hänsch optical coherence / optical frequency comb
How we tested QED: Experimental toolsBose-Einstein condensate
Long-interaction times
W Ketterle2001 Nobel lecture
Frequency comb locked to an atomic clock
How we tested QED: Experimental toolsKjeld Eikema
XUV: < 100 nm IR: > 800 nm
Optical ruler
1014 Hz 107 HzOptical frequencies Microwave frequencies
beat note
Frequency Comb
Accurate timebase
Load atoms into the optical dipole trap
Determine remaining atom number
Apply spectroscopy beam
Turn off the trap and record MCP signal
2 3S1 2 1S0(trapped) (anti-trapped)
How we tested QED: Experiment procedure
Recoil shift: ~20 kHzhv
p
AC Stark shift: ~ 1 kHz / 1 mW
Mean field shift: < 1 kHz (collisional shift)
How we tested QED: Systematics
(Energy shift due to external laser light)
Frequency comb: ~ 0.4 kHz (uncertainty in the time base)
(Momentum transfer)
MJ=+1
MJ=0
MJ=-1
fR FEnerg
y
0
B-field
How we tested QED: Results
4He:
3He:
Agreement with QED theory BUT
QED 1000 times less precise(challenge for theorists)
Relative Precision
192 510 702 145.6 (1.8) kHz
192 504 914 426.4 (1.5) kHz
9 x 10-12
8 x 10-12
Our Result
GWF Drake: Can J Phys 86 45-54 (2008)
Measure “identical” transitions in different isotopes: 3He, 4He
QED terms independent of /M cancel
Radiative recoil ~ 10 kHzcontribute to the uncertainty
How we tested nuclear few-body theory
Nuclear charge radius
)()()()43()43(
4232 QEDExperimentcc
HeHeHeHe
ffkHerHer
Only relative charge radii can be deduced.
To determine absolute charge radii the radius of the reference nucleus, 4He, must be known with the best possible precision
rc (4He) = 1.681(4) fm elastic electron scattering from 4He nucleus
GWF Drake: Can. J. Phys. 83: 311–325 (2005)
Measure “identical” transitions in different isotopes: 3He, 4He
How we tested nuclear few-body theory
Helium spectroscopy + QED:
Nuclear theory + scattering:
1.961(4) fm
1.965(13) fm
calculate the radius of the proton and the neutron the distribution in the nucleus
Summary
First time:
spectroscopy on ultracold trapped 4He and 3He
observation of the 1557 nm 2 3S1 → 2 1S0 transition
Challenge for absolute QED energy calculations to 8 x 10-12
Determined the size of the 3He nucleus to 4 x 10-18 m
LaserLaB Amsterdam:Rob van Rooij, Joe Borbely, Juliette Simonet ‡, Maarten Hoogerland ¶, Kjeld Eikema, Roel Rozendaal‡ ENS, Paris ¶ University of Auckland, New Zealand
MaartenJoe Juliette WV
Science 333, 196 (July 2011)
The metrology team
Rob
1. The classical Hanbury Brown -Twiss effect:
light as an electromagnetic
wave
2. Quantum Optics interpretation of the HBT
effect: light as a beam of photons
3. The HBT effect for atoms: 4He bosons
4. What about fermions? The 3He case.
Hanbury Brown Twiss effect for ultracold bosons and fermions
Quantum Optics (Wikipedia):
the study of the nature and effects of light as quantized photons
Before 1960: light interference understoodin electromagnetic wave picture, i.e. phase differences in amplitude of electric field
1956: Robert Hanbury Brown and Richard Twiss extended intensity interferometry tothe optical domain
Physics Nobel Prize 2005:Roy Glauber, Jan Hall, Ted Hänsch
~1963: birth of Quantum Optics
First-order coherence
g(1) gives the contrast in amplitude interference experiments (Young’s double slit, Michelson interferometer, interfering Bose condensates)
22
*
)1(
)()(
)()(),(
rErE
rErErrg
First order (phase) coherence: correlations in the amplitude of the field
= statistical average
(= time average for stationary process)
Hanbury Brown and Twiss:
Intensity correlations:
HBT effect: (second-order) correlations between two photocurrents at two different points and times.
22*
**
)2(
)(
)()(
)()(
)()()()(),(
rI
rIrI
rErE
rErErErErrg
2
21)1(
21)2( );,(1);,( rrgrrg
Measuring intensity correlations gives information on phase coherence: g(2) deviates from 1 for r < lc (correlation length)
g(2)(0,0,0) = 2 Do photons bunch?How can they? Independentparticles, no interactions !
g(2)
r
Nature, January 7, 1956
2
21122211 DSDSDSDSP
Hanbury Brown and Twiss
Quantum Optics interpretation Quantum Optics interpretation (Glauber):(Glauber):
interference of probability amplitudes interference of probability amplitudes of of indistinguishableindistinguishable processes: processes:
(bosons)light for 2 classicalPP
Correlation length = detector separation for which interference survives
Sum over all pairs S1 and S2 in the sourcewashes the interference out unless d is small enoughd
1)()2( rg
For a laser:
(Glauber’s coherent states)
2)2(
)(
)()(),(
rI
rIrIrrg
Intensity correlations:joint probability of detecting two photons at locations r and r’
For all chaotic sources (so no laser):
Should also work for atoms !(BEC is like a laser)
2)1()2( )(1)( rgrg
Shot noise (independent particles)
Correlations due tobeat notes of random waves
1965, 1966: Armstrong, Arecchi1965, 1966: Armstrong, Arecchi
First experiment: Yasuda and Shimizu, Ne* MOT (1996), heroic experiment, T=100 K
Amsterdam
OrsayOrsay
MCP (He* detector)63 cm below trap
Measurement of correlation of two particles emitted at S1 and S2 to be detected at D1 and D2
Position-sensitive MCP from Orsay to Amsterdam
Science Science 310310, 648 , 648 (2005)(2005)
VU experiment:
Thermal 4He atoms show bunching
Fit: l=0.56 +/- 0.08 mm
; i
i ms
tl
t: drop time
Agrees very well with theory!
; 2i
Bi m
Tks
T=0.5 K
(above BEC, si >> T)
2
21122211 DSDSDSDSP
What about fermionic atoms ?
For fermions we need an antisymmetric wavefunction:
fermions )(identicalfor 0P
d
Does not really surprise us:
Pauli principle!
Interference takes place when particles arrive within the same phase space cell: Δx Δy Δz Δpx Δpy Δpz < h3
Pure effect of quantum statistics:no classical interpretation possible !
Expected correlation function g(2)
(0,0,z)for bosons and fermionsfor bosons and fermions
Bosons
Fermions
4He
3He
T=0.5 K
Fit:• l=0.75 +/- 0.07 mm• l=0.56 +/- 0.08 mm
(difference due to masses 3 and 4)
2i
Bi
ii
m
Tks
ms
tl
t: drop time
Jeltes et al., Nature 445, 402 (2007)
Comparison of the Hanbury Brown Twiss effect for bosons and fermions
The HBT team
John Martijn
ValentinaTom
WV
Laser Centre Amsterdam: Tom Jeltes, John McNamara, Wim Hogervorst
Orsay: Valentina Krachmalnicoff, Martijn Schellekens, Aurelien Perrin, Hong Chang, Denis Boiron, Alain Aspect, Chris Westbrook
Nature 445, 402 (2007)
KenBaldwin