optical clocks, present and future fundamental physics tests
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Optical clocks, present and future fundamental physics tests. Pierre Lemonde LNE-SYRTE. Fractional accuracy of atomic clocks. Systematic effects-accuracy. Zeeman effect: Independent on the clock transition frequency Spectral purity, leakage,...: - PowerPoint PPT PresentationTRANSCRIPT
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Optical clocks, present and Optical clocks, present and future fundamental physics tests future fundamental physics tests
Pierre Lemonde
LNE-SYRTE
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Fractional accuracy of atomic clocksFractional accuracy of atomic clocks
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Systematic 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
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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 clocks
<10-18
Q~4 1014, N~106, Tc ~ 1s
Single ion clocks an neutral atom lattice clocks are two possible ways forward
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Multipolar couplings: E2, E3
Intercombination transitions
Quantum 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)
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Quantum 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
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Al+ clocksAl+ clocks
C. Chou et al. PRL 104 070802 (2010)
C. Chou et al. Science 329, 1630 (2010)
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Al+ clock accuracy budgetAl+ clock accuracy budget
C. Chou et al. PRL 104 070802 (2010)
Ion clock with sub 10-17 accuracy
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Neutral atom clocksNeutral atom clocks
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Trapping 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
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Problems 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)
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Solution to the trapping problemSolution to the trapping problemPolarisation : 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"
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Experimental setupExperimental setup
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Ultra-narrow resonance
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Lattice clock comparison
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Trap effects
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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
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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
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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
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Trap 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
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8787Sr 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 ?
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Towards 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)
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Optical 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
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Clock comparisons
• « Round-trip » method for noise compensation
Round-trip noise detection
LAB 1
AccumulatedPhase noise
Ultra-stable 1.542 µm laser
Noise correction
LAB 2PP
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)
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Fundamental 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
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Optical 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
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main requirements:1. compact design2. reliability3. low power consumption
optical breadboard 120 cm x 90 cm
Transportable 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)
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ConclusionsConclusions
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 ?