Report

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 Potential gain 104 Spectral purity, leakage,...: – Independent on the clock transition frequency Potential gain 104 Cold collisions: – Independent on the clock transition frequency Potential gain 104 Neighbouring transitions: – Independent on the clock transition frequency Potential gain 104 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 Potential gain 102 @ Optical frequencies all these effects seem controllable at 10-18 or better ! • Doppler effect: – Proportional to the clock frequency for free atoms, a trap is required Interest of optical clocks Ultimate gain on the frequency stability : 104 Q~4 1014, N~106, Tc ~ 1s Ultimate gain on the frequency accuracy > 102 <10-18 -A « good » clock transition Key ingredients -Ability to control external degrees of freedom. -Ultra-stable lasers Single ion clocks an neutral atom lattice clocks are two possible ways forward Quantum references: ions or atoms Multipolar couplings: E2, E3 2P 2P 1/2 2D 3/2 1/2 2D 5/2 369 nm 422 nm d=3 Hz 674 nm 467 nm d=0.4Hz 2S 2F 7/2 436 nm 2S 1/2 d=10-9 Hz 1/2 Yb+(PTB, NPL) Sr+ (NPL,NRC) Other ions: Hg+ (NIST), Ca+(Innsbruck, Osaka, PIIM) Intercombination transitions 1P 1P 1 3P 461 nm 698 nm 1 3P 0 167 nm 267 nm d=1 mHz 1S 0 Sr (Tokyo, JILA, SYRTE,…), Yb (NIST, INRIM, Tokyo,…) Hg (SYRTE, Tokyo), In+ d=8 mHz 1S 0 Al+ (NIST) 0 Quantum logic clock One logic ion for cooling and detection One clock ion for spectroscopy External degrees of freedom are coupled via Coulomb interaction Al+ clocks C. Chou et al. Science 329, 1630 (2010) C. Chou et al. PRL 104 070802 (2010) Al+ clock accuracy budget Ion clock with sub 10-17 accuracy C. Chou et al. PRL 104 070802 (2010) Neutral atom clocks Trapping neutral atoms Confinement : standing wave Trapping : dipole force (intense laser) 1 0.5 0 Optical lattice clocks 0 -2.5 -5 -7.5 -10 Trap shifts -0.5 -0.25 0 0.25 0.5 l/2 D> 10-10 reaching 10-18, effect must be controlled to within 10-8 Problems linked to trapping Trap 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 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 3P 0 3S 1 Sr 679 nm 1S 1P 1 0 lm : "longueur d'onde magique" M. Takamoto et al, Nature 453, 231 (2005) 461 nm 1S 3D 1 3P 0 698 nm 0 2.56 µm Experimental setup Ultra-narrow resonance Lattice clock comparison Trap 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 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 effects Measurements 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 shifts •Hyperpolarisability d<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 87Sr 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 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 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 comparisons • « Round-trip » method for noise compensation Ultra-stable 1.542 µm laser Noise correction 2FP Fiber Accumulated Phase noise LAB 1 FP LAB 2 Round-trip noise detection Link instability measurement • 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 ground • Stability of fundamental constants a/a expected improvement by 2 orders of magnitude 10-18/yr m/m limited by microwave clocks. Possible improvements if nuclear transitions are used. • Dependence of a to local gravitational potential – Expected improvement by 2 orders of magnitude 10-8 d(GM/rc2) • Massive redondancy due to the large number of atomic species/transitions 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). S. Schiller et al. Exp. Astron. (2009) 23, 573 • Solar system probe – Outer solar system (SAGAS-like). Further improvement by 2 orders of magnitude on gravitational red-shift and coupling of a to gravity. Probe long range gravity. – Inner solar system. Probe GR in high field. P. Wolf et al. Exp. Astron. (2009) 23, 651 Transportable Strontium Source (LENS/U.Firenze)-SOC project main requirements: 1. compact design 2. reliability 3. low power consumption optical breadboard 120 cm x 90 cm main planning choices: 1. compact breadboard for frequency production 2. all lights fiber delivered 3. custom flange holding MOT coils and oven with 2D cooling Schioppo et al, Proc. EFTF (2010) Conclusions 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 ?