optical clocks, present and future fundamental physics tests pierre lemonde lne-syrte
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Optical clocks, present and Optical clocks, present and future fundamental physics tests future fundamental physics tests
Optical clocks, present and Optical clocks, present and future fundamental physics tests future fundamental physics tests
Pierre Lemonde
LNE-SYRTE
Fractional accuracy of atomic clocksFractional accuracy of atomic clocksFractional accuracy of atomic clocksFractional accuracy of atomic clocks
Systematic effects-accuracySystematic effects-accuracySystematic effects-accuracySystematic effects-accuracy
• Zeeman effect: – Independent on the clock transition frequency
• Spectral purity, leakage,...: – Independent on the clock transition frequency
• Cold collisions: – Independent on the clock transition frequency
• Neighbouring transitions: – Independent on the clock transition frequency
• Blackbody radiation shift: differential in fountains– Cs: 1.7 10-14, Sr, Yb ~ 5 10-15, Hg : 2.4 10-16, Al+ 8 10-18
• Doppler effect: – Proportional to the clock frequency for free atoms, a trap is required
@ Optical frequencies all these effects seem controllable at 10-18 or better !
Potential gain 104
Potential gain 104
Potential gain 104
Potential gain 104
Potential gain 102
Ultimate gain on the frequency stability : 104
Ultimate gain on the frequency accuracy > 102
Key ingredients
-A « good » clock transition
-Ability to control external degrees of freedom.
-Ultra-stable lasers
Interest of optical clocksInterest of optical clocksInterest of optical clocksInterest of optical clocks
<10-18
Q~4 1014, N~106, Tc ~ 1s
Single ion clocks an neutral atom lattice clocks are two possible ways forward
Multipolar couplings: E2, E3
Intercombination transitions
Quantum references: ions or atomsQuantum references: ions or atomsQuantum references: ions or atomsQuantum references: ions or atoms
2P1/2
Sr+ (NPL,NRC)
=0.4Hz2S1/2
2P1/2
2D5/2
422 nm674 nm
2S1/2
2D3/2
2F7/2
Yb+(PTB, NPL)
369 nm 436 nm
467 nm
=3 Hz
=10-9 Hz
Other ions: Hg+ (NIST), Ca+(Innsbruck, Osaka, PIIM)
Sr (Tokyo, JILA, SYRTE,…), Yb (NIST, INRIM, Tokyo,…) Hg (SYRTE, Tokyo), In+
=1 mHz1S0
1P1
3P0
461 nm698 nm
=8 mHz1S0
1P1
3P0
167 nm267 nm
Al+ (NIST)
Quantum logic clockQuantum logic clockQuantum logic clockQuantum logic clock
One logic ion for cooling and detection
One clock ion for spectroscopy
External degrees of freedom are coupled via Coulomb interaction
Al+ clocksAl+ clocksAl+ clocksAl+ clocks
C. Chou et al. PRL 104 070802 (2010)
C. Chou et al. Science 329, 1630 (2010)
Al+ clock accuracy budgetAl+ clock accuracy budgetAl+ clock accuracy budgetAl+ clock accuracy budget
C. Chou et al. PRL 104 070802 (2010)
Ion clock with sub 10-17 accuracy
Trapping neutral atomsTrapping neutral atomsTrapping neutral atomsTrapping neutral atoms
Trapping : dipole force(intense laser)
-0.5
-0.25
0
0.25
0.5
0
0.5
1
-10
-7.5
-5
-2.5
0
-0.5
-0.25
0
0.25
0.5
0
0.5
1
/2
Confinement : standing wave
Optical lattice clocks
Trap shifts
> 10-10
reaching 10-18, effect must be controlled to within 10-8
Problems linked to trappingProblems linked to trappingProblems linked to trappingProblems linked to trappingTrap depth : light shift of clock states
3 parameters : polarisation, frequency, intensity
Trap depth required to cancel motional effects to within 10-
18 : at least 10 Er (i.e. 36 kHz, or 10-11 in fractional units for Sr)
Both states are shifted. The differential shift should be considered P. Lemonde, P. Wolf, Phys. Rev. A 72 033409 (2005)
Solution to the trapping problemSolution to the trapping problemSolution to the trapping problemSolution to the trapping problem
Polarisation : use J=0 J=0 transition, which is a forbidden by selection rules
Intensity : one uses the frequency dependence to cancel the intensity dependence
Such a configuration exists for alkaline earths 1S0 3P0
1S0
3D1
3S1
1P1
3P0
698 nm
461 nm2.56 µm
679 nmSr
M. Takamoto et al, Nature 453, 231 (2005)
1S0
3P0
m : "longueur d'onde magique"
E2-M1 Effects E2-M1 Effects E2-M1 Effects E2-M1 Effects
E1 interaction
Traps atoms at the electric field maxima
M1 and E2 interactions
Creates a potential with a different spatial dependence
E2-M1 Effects E2-M1 Effects E2-M1 Effects E2-M1 Effects
E1 interaction
Traps atoms at the electric field maxima
M1 and E2 interactions
Creates a potential with a different spatial dependence
This leads to a clock shift
E2-M1 effectsE2-M1 effects E2-M1 effectsE2-M1 effectsMeasurements
The shift is measured by changing n and the trap depth U0=100-500 Er
•The effect is not resolved, not a problem
•Upper bound 10-17 for U0=800 Er
Trap shiftsTrap shifts
•Hyperpolarisability
<1 µHz/Er2
•Tensor and vector shift. Fully caracterized and under control <10-17
•All known trap effects are well understood and not problematic <10-17
P.G. Westergaard et al., arxiv 1102.1797
8787Sr lattice clock accuracy budgetSr lattice clock accuracy budget8787Sr lattice clock accuracy budgetSr lattice clock accuracy budget
A. Ludlow et al. Science, 319, 1805 (2008)
• Frequency difference between Sr clocks at SYRTE <10-16
• 10-17 feasible at room temperature. BBR, a quite hard limit. Next step: cryogenic, Hg ?
Towards a Hg lattice clockTowards a Hg lattice clockTowards a Hg lattice clockTowards a Hg lattice clock
• First lattice bound spectroscopy of Hg atoms
• First experimental determination of Hg magic wavelength 362.53 (21) nm
L. Yi et al., Phys. Rev. Lett. 106, 073005 (2011)
Optical clocks worldwideOptical clocks worldwide
• Ion clocks– NIST (Al+, Hg+), PTB-QUEST (Yb+, Al+), NPL (Yb+, Sr+),
Innsbruck (Ca+)…
• Neutral atom clocks – Tokyo (Sr, Hg), JILA (Sr), SYRTE (Sr, Hg), NIST (Yb), PTB (Sr),
…
• Space projects– SOC project (ESA – HHUD, PTB, SYRTE, U-Firenze)– SOC2 (EU-FP7)– Optical clock as an option for STE-QUEST mission
Performing fundamental physics tests implies comparing these clocks
Clock comparisonsClock comparisons
• « Round-trip » method for noise compensation
Round-trip noise detection
LAB 1
AccumulatedPhase noise
Ultra-stable 1.542 µm laser
Noise correction
LAB 2P
P
Link instabilitymeasurement
Fiber
• Demonstrated at the 10-19 level over hundreds of km over telecom network
• Global comparisons = satellite based systems
•ACES-MWL 2014-2017 down to a few 10-17, L. Cacciapuoti (next talk)
•Mini-DOLL coherent optical link, K. Djerroud et al. Opt. Lett. 35, 1479 (2009)
Fundamental tests on groundFundamental tests on ground
• Stability of fundamental constants expected improvement by 2 orders of magnitude 10-18/yr limited by microwave clocks. Possible improvements if
nuclear transitions are used.
• Dependence of to local gravitational potential– Expected improvement by 2 orders of magnitude 10-8 (GM/rc2)
• Massive redondancy due to the large number of atomic species/transitions
Optical clocks in spaceOptical clocks in space
• Earth orbit– Highly elliptical orbit. x100 improvement on ACES goals– Optional optical clock for STE-QUEST mission (pre-selected as
M mission in CV2).
• Solar system probe – Outer solar system (SAGAS-like). Further improvement by 2
orders of magnitude on gravitational red-shift and coupling of to gravity. Probe long range gravity.
– Inner solar system. Probe GR in high field.
S. Schiller et al. Exp. Astron. (2009) 23, 573
P. Wolf et al. Exp. Astron. (2009) 23, 651
main requirements:1. compact design2. reliability3. low power consumption
optical breadboard 120 cm x 90 cm
Transportable Strontium Source (LENS/U.Firenze)-SOC projectTransportable Strontium Source (LENS/U.Firenze)-SOC project
main planning choices:1. compact breadboard for frequency production2. all lights fiber delivered3. custom flange holding MOT coils and oven with 2D cooling
Schioppo et al, Proc. EFTF (2010)
ConclusionsConclusionsConclusionsConclusions
Optival clocks with ions and neutrals now clearly outperform microwave standards. Present accuracy and long term stability 10-17 .
Where is the limit ?
Long distance comparisons techniques are progressing rapidly.
Different types of clocks, using different atoms and different kind of transitions allow extremely complete tests of fundamental physics: stability of fundamental constants, probing gravity and couplings to other interactions. Redondancy is important in case violations are seen.
Space projects.
Further improvements ? Higher frequencies (UV-X) ? Nuclear transitions ? Molecular transitions ?
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