Lecture 3 Applications of Ultra-stable Clocks

Transcription

1 Lecture 3 Applications of Ultra-stable Clocks C. Salomon Laboratoire Kastler Brossel, Ecole Normale Supérieure, Paris BIPM Summer school, July 25, 2003

2 Outline 1) Cesium versus Rubidium fountain clocks 2) Frequency measurements in the optical domain Femtosecond laser 3) Search for variations of fundamental constants 4) Beyond fountains New types of clocks, clocks in space 5) Perspectives

3 A serious limit in Cesium fountains: Collisional Frequency Shift Shift proportional to density n, hence to number of detected atoms N at With Cs, extrapolation to N at = 0 is necessary Density is prop. to N at only if volume remains constant A new method to measure the collisional shift at 1% level: rapid adiabatic passage. Relative Frequency Shift (10-16 ) The ratio of density is 1/2-120 with a 1% accuracy (Pereira Dos Santos et al., PRL 2002) The method can reach a 0.1% accuracy Fit : September y= x January 2000 Fit : y= x Uncertainty on the slope < 10% 0 2e+5 4e+5 6e+5 8e+5 1e+6 Detected Atoms

4 87 Rb BNM-SYRTE 87 Rb fountain Based on 87 Rb BEC measurements, theoreticians predicted in 1997 that shift in Rb was 15 times smaller than in Cs

5 Collisional Shift in F=1,m 87 F =0 : 87 Rb vs 133 Cs SYRTE YALE Measurement frequency resolution : The 87 Rb shift is 70 times smaller than in 133 Cs

6 Applications of atomic clocks Navigation, Positioning GPS, GLONASS, deep space probes Geodesy Datation of millisecond pulsars VLBI Synchronisation of distant clocks TAI Fundamental physics tests Ex : general relativity Einstein effect, gravitational red-shift : Shapiro delay : Search for a drift of the fine structure constant α : α d α / dt at 10 / year 1 16

7 Long distance comparison between PTB and NIST Cesium Fountains Frequency Comparison NIST F1 - CSF1 (period of overlap, date of measurement) x y(f1 - CSF1) (15 days, August 2000) (10 days, July 2001) (20 days, November 2001) BIPM circular T data base of clock comparisons using GPS or TWSTFT Number of Measurement

8 A transportable cold atom clock

9 PHARAO in inparabolic flights in in ZeroG Airbus Mai 1997

10 PHARAO: a Transportable Fountain Measurement of 1S-2S transition of Hydrogen at Max Planck Institut für Quantenoptik in Garching atomic hydrogen cryostat Faraday cage 2S detector chopper vacuum chamber x nm dye laser time resolved photon counting ν 1S-2S = (46) Hz Accuracy : f dye 486 nm M. Niering et al, P.R.L. 85, June 2000 I 4/7 x f dye x4/7 x1/2 1/2 x f dye λ microwave interaction cold atom source Multiplication by of the cesium frequency to the UV range, 243 nm 70 fs Ti:sapphire mode locked laser 9.2 GHz detection

11 Femtosecond Laser Pulsed laser, repetition rate: 840 MHz J. Reichert et al. PRL 84, 3232 (2000), S. Diddams et al. PRL 84,5102 (2000) A. Brusch, D.B. Kolker, G.D. Rovera

12 Frequency comb ν Offset n f rep b ν at f rep = 840 MHz ν=0 ν at n n-1 n+1 ν = b+ n f + at rep ν offset 1) Bring ν offset to 0 2) Use fountain clock to drive the rep. rate

13 Einstein Equivalence Principle and the stability of fundamental constants In any free falling local reference frame, the result of a non gravitational measurement should not depend upon when it is performed and where it is performed. EEP ensures the universality of the definition of the second It implies the stability of fundamental constants: α=e 2 /hc, m e, m p, In particular: the ratio of the transition frequencies in different atoms and molecules should not vary with space and time The EEP can be tested by high resolution frequency measurements regardless of any theoretical assumption EEP revisited by modern theories: g µν g µν,ϕ, Fundamental constants depend upon local value of ϕ : α(ϕ), m(ϕ), Violations of EEP are expected at some level!! For instance: T. Damour, G. Veneziano, PRL 2002

14 Does the fine structure constant α varies with time? Because of large relativistic corrections, the hyperfine energy of an alkali atom depends upon Z and α=e 2 /ħc Search method for α drift: Compare hyperfine energy of rubidium and cesium as function of time

15 Present tests of cosmological Variations of α Oklo test : geochemical analysis of the natural fossil fission reactor in Oklo (Gabon, yr ago) : α now α Damour, Poliakov, Nucl. Phys. B 480, 37 (1996) Absorption spectroscopy from quasars: α α = Oklo α ( 0.72 ± 0.18 ) 10 (0.5< z< 3.5) J. Webb et al., PRL 87, (2001) α& 17 yr 1

16 Laboratory tests versus cosmological tests A priori loss of factor in sensitivity!! ~ 1 year versus years But: ultra-stable and accurate clocks: 10-15! repeatable measurements independent checks in various labs choice of hyperfine, fine and optical transitions See S. Karshenboim, Can. J. Phys , (2000), J.P. Uzan (2002)

17 87 87 Rb Cs Comparison over 5 years 10 Relative frequency (10-15 ) υ Rb = ( 12) Hz Year Within Prestage et al. theoretical framework : d υ Rb 16 ln = ( 0.2 ± 7) 10 / year dt υcs & α 16 = ( 0.4 ± 16) 10 / year α H. Marion et al., PRL (2003)

18 Beyond fountains Clock quality: ν 0 T Increase clock frequency: optical clocks Increase interrogation time Trapping atoms microgravity in a satellite: PHARAO project, ESA-CNES, BNM-SYRTE, ENS, ON PARCS project: NIST, JPL, NASA RACE project: Penn ST., JPL, NASA

19 Towards an optical clock Toward an optical cold atom clock with Cold cold Strontium strontium Atoms atoms P. Lemonde, I. Courtillot, A. Quessada, R. Kovacich, BNM-SYRTE λ = 689 nm

20 Towards an optical clock with fermionic Strontium : Sr 1 P nm (32 MHz) 671 nm (10-5 Hz) 3 P S nm (7.6 khz) 698 nm ( 87 Sr: 1 mhz) I. Courtillot, A. Quessada, R. Kovacich, A. Brusch, D. Kolker, J. J. Zondy, G. Rovera, and P. Lemonde arxiv:physics/

21 87 87 Sr optical clock Method: (H. Katori) Interrogate atoms in optical lattice without frequency shift Long interaction time Large atom number (10 8 ) Lamb-Dicke regime Excellent frequency stability Small frequency shifts: No collisions (fermion) No recoil effect (confinement below optical wavelength) Small Zeeman shifts (only nuclear magnetic moments)

22 Space Clocks ESA, CNES, SYRTE NASA, JPL, NIST

23 Atomic Atomic Clock Clock in in Space Space Thermal beam : v = 100 m/s, T = 5 ms ν = 100 Hz Fountain : v = 4 m/s, T = 0.5 s ν = 1 Hz PHARAO : v = 0.05 m/s, T = 5 s ν = 0.1 Hz

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25 Cooling zone Selection PHARAO cold atom clock Ramsey Interrogation Mass 91 kg Power 110 W L=1m detection Cesium reservoir Microwave cavity 3 Magnetic shields and solenoids Fountain : v = 4 m/s, T = 0.5 s PHARAO : v = 0.05 m/s, T = 5 s ν = 1 Hz ν = 0.1 Hz Ion pump

26 ACES: Atomic Clocks Ensemble in Space PHARAO H-MASER A cold atom Cs standard in space Worldwide access Fundamental physics tests

27 A Prediction of General Relativity ν ν U2 U1 c 2 = ( = 0 ) 10 U Terre h c Redshift measurement at : R. Vessot et al., 1976

28 E Relativity tests on ISS Red shift Comparaison of absolute frequencies of space clock ς S and ground clock ς E ν ν S E ν U = = + = + ν ν c E ( 1 α) ( 1 α) gh c 2 2 Einstein : α =0at (Vessot, Levine 76) At Η = 450kms : ς /ς = With clock accuracy of 10-16, the red-shift can be measured at Factor 25 improvement Second order Doppler effect: -1/2 v 2 / c 2 =

29 ACES on the ISS

30 ACES ON COLUMBUS EXTERNAL PLATFORM ACES M = 227 kg P = 450 W Launch date : end of 2006 Mission duration : 18 months

31 Atomic Clock Ensemble in in Space PHARAO : Cold Atom Clock in Space. CNES (France) A. Clairon, P. Laurent, P. Lemonde, M. Abgrall, S. Zhang, C. Mandache, F. Allard, M. Maximovic, F. Pereira, G. Santarelli, Y. Sortais, S. Bize, P. Rosenbusch, H. Marion, D. Calonico, N. Dimarcq, (BNM-SYRTE), C. Salomon (ENS) SHM : Space Hydrogen Maser. ON (Switzerland) A. Jornod, D. Goujon, L.G. Bernier, P. Thomann MWL : Microwave link. Kayser-Threde-Timetech (Germany) W. Schaefer, S. Bedrich, S. Fockersperger, F. Huber ACES payload: Astrium ACES is open to any interested scientific user W. Knabe, P. Wolf, L. Blanchet, P. Teyssandier, P. Uhrich, A. Spallici New members : 2001: UWA (Australia), A. Luiten, M. Tobar, J. Hartnett, C. Locke, R. Kovacich 2002: LENS (Italy), G. Tino, G. Ferrari, L. Caciapuotti ESA: MSM S. Feltham, F. Reina, I. Aguilar-Sanchez CNES: C. Sirmain + team of 20 engineers at CST, Toulouse

32 Perspectives (1) Microwave Clocks Rubidium fountains have the potential to surpass Cesium by one order of magnitude: Cs: stability per day, accuracy: ~ Rb: a few with cryogenic local oscillator Comparisons between distant clocks at using ACES in 2006 Currently, clock transport!! Or major improvements of microwave and optical links Wide domain of applications Fundamental physics, navigation, geodesy, Time and frequency metrology Clocks with entangled states? Demonstrated with two ions at NIST Stability as 1/N instead of 1/N 1/2

33 Clocks of the future < Q= ν/ ν= 2 ν T Increase the frequency: optical clocks Neutral atoms: Ca, Sr, Mg, Ag, better performance in space Trapped ions : Hg +, In +, Yb + In both cases: Ultra-stable lasers with emission linewidth << 1 Hz, B. Young et al., PRL 82, 3799 (1999) Frequency comb with femtosecond laser connects the microwave domain to visible domain with a simple device Large improvement of tests of variations of α, g p, M e / M p

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35 Laboratory tests of α variations using clocks Relativistic corrections : the energy levels of the frequencies of two different alkalis depend on α and Z 1, Z 2 The ratio of the hyperfine energies of different atomic species explicitely depends on α=e 2 /ħc d dt υ ln = υ 1 [ L F ( α, Z ) L F ( α Z )] 2 d rel 2 d rel, Hg+ vs H : Prestage et al., PRL 74, 3511 (1995) 1 & α = K α 21 & α α

36 The twin fountain Cs-Rb Simultaneous operation With Cs and Rb Better test over α Target: dα/dt at /year