Cold Atom Atom Clocks Clocks Cold Cold Atom Clocks and - PowerPoint PPT Presentation

Cold Atom Atom Clocks Clocks Cold Cold Atom Clocks and Fundamental Fundamental Tests Tests and and Fundamental Tests C. Salomon Laboratoire Kastler Brossel, Ecole Normale Supérieure, Paris http://www.lkb.ens.fr/recherche/atfroids/welcome TAM, Bled, Slovenia, August 2007

Participants Participants Participants M. Abgrall, S. Zhang, Y. Maksimovic, F. Allard, C. Vian, F. Chapelet, C. Jentsch, C. Mandache, S. Bize, P. Lemonde, P. Laurent, G. Santarelli, P. Rosenbusch, P. Wolf, A. Clairon Laboratoire National d’essais Systèmes de Références Temps-Espace, SYRTE Observatoire de Paris ACES Science Team And in particular: M. Tobar, J. Hartnett, A. Luiten, University of Western Australia D. Svehla, TU Muenchen, M. Ziebart, M. Rothacher L. Blanchet, P. Teyssandier, L. Lusanna P. Berthoud, M. Roulet (ON) ESA ACES project and L. Cacciapuoti CNES PHARAO team and C. Sirmain, D. Massonnet

Summary Summary Summary 1) What is an atomic clock ? Frequency stability Accuracy 2) Atomic fountains and optical clocks Performances 3) Fundamental tests with space clocks Redshift measurement Search for drift of fundamental constants 4) ACES applications Geodesy, GNSS

Time measurement measurement Time Time measurement Find a periodic phenomenon: 1) Nature: observation: Earth rotation, moon rotation, orbit of pulsars,.. 2) Human realization: egyptian sandstone, Galileo pendulum…. simple phenomenon described by a small number of parameters The faster the pendulum, The better is time resolution = π T l g 2 /

Time measurement measurement (2) (2) Time Time measurement (2) Electromagnetic field: Quartz oscillator,… vibration of crystal coupled to an electrical circuit Atomic Clock: Intrinsic stability of energy levels (Quantum Mechanics) Control of atomic motion Laser cooling: low velocities : 1 cm/s Long measurement time: Narrow atomic resonance Better clocks

Precision of Time Precision of Time 1s 1ms 1 μ s 1ns 100 ps ps/ /day day 100 10 ps ps/ /day day 10 1ps

E b Atomic Clock υ A h E a An oscillator of frequency ν produces an electromagnetic wave Δν which excites a transition a - b ν Α The transition probability a → b as a function of ν has the shape Atomic transition transition Atomic of a resonance curve centred in ν A = (E b -E a ) / h and of width Δν A servo system forces ν to stay equal to the atomic Oscillator Oscillator frequency ν A An atomic clock is an oscillator whose frequency is locked to that of an atomic transition The smaller Δν, the better is the precision of the lock system

Atomic clock Atomic clock Definition of the second : The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground electronic state of cesium 133 Intrinsic stability of atomic energy levels Laser cooling to 1 µK Corresponding to rms velocity of 7mm/s 1) Fountain geometry 2) Microgravity environment F=4 υ = 1. Stability 9 192 631 770 Hz 6 S 1/2 0 2. Accuracy F=3

Ramsey fringes fringes in in atomic atomic fountain fountain Ramsey Ramsey fringes in atomic fountain S/N= 5000 per point

Cesium clock Stability/Accuracy: State of the art Cesium clock Stability/Accuracy: State of the art Cesium clock Stability/Accuracy: State of the art ν clock (t) = ν cesium (1+ ε+ y ( t )) Where ν cesium is the transition frequency of a cesium atom at rest in absence of perturbation ε : frequency shift, ε = ε 1 + ε 2 + ε 3 +…. y(t): frequency fluctuations with zero mean value. Accuracy: ε To what extent does the clock realize the definition of the second? Cesium and rubidium fountains: ε ~ 3 10 -16 Frequency stability Measurement duration τ : y( τ ) averaged frequency instability For τ = 1s, y( τ ) = 1.4 10 -14 fundamental quantum limit For τ = 50 000 s , y( τ ) ~ 1.4 x 10 -16

Atomic Fountains Fountains Atomic Atomic Fountains 14 fountains in operation at SYRTE, PTB, NIST, USNO, JPL, Penn St, INRIM, NPL, ON. 6 with accuracy at 1 10 -15 . More than 10 under construction. PTB, D LNE-SYRTE, FR NIST, USA cs19

Comparison between two Cesium Fountains Comparison between two Cesium Fountains FO1 and FO2 (Paris) FO1 and FO2 (Paris) cs20 τ −1/2 S. Bize et al. τ τ C. Rendus Acad. Sciences 2004 SYRTE τ τ Measured Stability: 1.4 10 -16 at 50 000 s Best measured stability for fountains ! Factor 5-10/Hydrogen Maser Agreement between the Cesium frequencies: 4 10 -16

A transportable cold atom atom clock clock A transportable cold A transportable cold atom clock Transport to Bordeaux: 1997 MPQ:1999, 2003 PTB: 2002 Innsbruck 2007

PHARAO in parabolic parabolic flights flights PHARAO in PHARAO in parabolic flights in ZeroG ZeroG Airbus Airbus in in ZeroG Airbus Mai 1997

Frequency Comb Frequency Comb J. Reichert et al. PRL 84 , 3232 (2000), S. Diddams et al. PRL 84 ,5102 (2000)

Connecting microwaves microwaves to to Connecting Connecting microwaves to optical frequencies frequencies optical optical frequencies Measurement of 1S-2S transition of Hydrogen at MPQ in Hänsch lab Using the mobile cold atom fountain ν 1S-2S = 2 466 061 413 187 103 (46) Hz cryostat atomic hydrogen 2S detector Faraday cage Accuracy : 1.8 10 -14 vacuum chamber chopper M. Niering et al, P.R.L. 85 , (2000) x 2 243 nm time resolved M. Fischer et al., PRL, 92 (2004) photon counting dye laser Multiplication by 250 000 f dye 486 nm of the cesium frequency to the UV range, 243 nm x4/7 x1/2 microwave 4/7 x f dye 1/2 x f dye interaction I New limits on time change of fundamental constants, α and strong interaction constant λ cold atom source 70 fs Ti:sapphire detection mode locked laser 9.2 GHz

Search for variations of for variations of fundamental fundamental constants constants Search Search for variations of fundamental constants and Einstein Equivalence Principle Principle and Einstein Equivalence and Einstein Equivalence Principle 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 ensures the the universality universality of the of the definition definition of the second of the second EEP It implies the stability of fundamental constants: α =e 2 /4 πε 0 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 cs18

87 Rb - 133 Cs Comparison over 6 years 87 Rb - 133 Cs Comparison over 6 years 10 10 -15 ) -15 ) 5 5 Relative frequency (10 Relative frequency (10 0 0 -5 -5 -10 -10 ( ) Hz υ Rb = . 6 834 682 610 904 335 12 -15 -15 -20 -20 1997 1997 1998 1998 1999 1999 2000 2000 2001 2001 2002 2002 2003 2003 2004 2004 Year Year ⎛ ⎞ = − d υ ( ) ± × − Rb year 16 ⎜ ⎟ ln 0.5 5.3 10 / H. Marion et al., dt υ ⎝ ⎠ Cs PRL (2003), Bize 2004 Within Prestage et al . α � ( ) = ± × − / year 16 1.0 12 10 theoretical framework : α

Applications of atomic atomic clocks clocks Applications of Applications of atomic clocks • Navigation, Positioning GPS, GLONASS, deep space probes • Datation of millisecond pulsars • VLBI • Synchronisation of distant clocks TAI • Geodesy • Fundamental physics tests Ex : general relativity Einstein effect, gravitational red-shift : 10 -4 10 -6 Shapiro delay : 10 -3 10 -7 Search for a drift of fundamental constants such as the fine − − structure constant α : α α 1 1 7 d / d t a t 1 0 / y e a r

Fundamental Tests Tests with with space space Clocks Clocks Fundamental Fundamental Tests with space Clocks 1997

• A cold atom Cesium clock in space • Fundamental physics tests • Worldwide access ACES atomic clocks

ACES on the ISS ACES on the ISS ACES on the ISS H= 400km T= 5400 s V=7km/s

A Prediction Prediction of General of General Relativity Relativity A A Prediction of General Relativity Einstein gravitational gravitational shift shift Einstein Einstein gravitational shift U 1 U 2 U 2 − ⎛ ⎞ ν U U = − ⎜ ⎟ 2 2 1 1 ν ⎝ c ⎠ 2 1 Redshift : +4.59 10 -11 with 10 -16 clocks ACES: 2 10 -6 Factor 35 gain over GP-A 1976

ACES and variations of fundamental fundamental ACES and variations of ACES and variations of fundamental physical constants constants physical physical constants G, α elm , α strong , m e ,… Principle : Compare two or several clocks of different nature as a function of time Microwave clock/Microwave clock Very stringent limits on variations of α elm , α strong , m e /m p rubidium and cesium Sensitivity: 10 -17 /year Microwave / Optical clock Optical Clock / Optical clock Today: α/α < 1-3 10 -16 / year, Fortier et al. 2007