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Atomic Clocks in Space

Atomic Clocks in Space. L. Cacciapuoti ESA-ESTEC (SCI-SP). Local oscillator. Clock output. Correction. Atomic sample. Interrogation. Inaccuracy: e Fractional frequency fluctuations: y(t) Fractional frequency instability: Fluctuations of the transition probability:

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Atomic Clocks in Space

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  1. Atomic Clocks in Space L. Cacciapuoti ESA-ESTEC (SCI-SP)

  2. Local oscillator Clock output Correction Atomic sample Interrogation Inaccuracy: e Fractional frequency fluctuations: y(t) Fractional frequency instability: Fluctuations of the transition probability: Atomic quality factor: Transition probability Detuning Atomic Clocks: Basic Principles

  3. Cs-Rb fountain clock FO2 Nat ~ 109 s ~ 3 mm T ~ 1 mK v ~ 4 m/s H ~ 1 m 100 ms ≤ Tload ≤ 500 ms 1.1 s ≤ Tcycle ≤ 1.5 s Atomic Fountain Clocks

  4. Linewidth: 0.94 Hz Quality factor: Qat= 9.82109 S/N ratio: 1/sdP ~ 5000 Ramsey Fringes

  5. Fractional frequency instability Performances of FO2

  6. Thermal beam Cold atoms Cold atoms in microgravity Atomic Fountain Clocks in Space Benefits from Space • Weightlessness • Long interrogation times • Narrow clock transitions • Linewidth: 100 mHz • Instability: 710-14 at 1 s 310-16 at 1 day • Accuracy: ~ 10-16 • Low mechanical vibrations • Possibility of worldwide access

  7. The Mission

  8. MWL Ku- and S-band antennas PDU FCDP MWL PHARAO UGB Heat pipes XPLC SHM CU and PSU SHM RFU CEPA ACES base-plate SHM cavity assembly PHARAO laser source PHARAO accelerometer and coils control unit SHM HDA PHARAO tube The ACES Payload Volume: 1172x867x1246 mm3 Total mass: 227 kg Power: 450 W

  9. PHARAO: A Cold-Atom Clock in -gravity

  10. Power of the cooling laser at the fibers output Capture 3 x 14 mW + 3 x 12 mW Relative phase noise between the 6 cooling beams: ~0.25 mrad rms (100 Hz - 100 kHz) Detection system Standing wave (F=4) Pushing beam (F=4) Pumping beam (F=3) Standing wave (F=4) PHARAO Optical System

  11. Physics Package Microwave Cavity and Shields Assembly H2 Dissociator Low Noise Amplifier External Structure Ion Pumps High Voltage Unit Power Supply Unit Hydrogen DistributionAssembly Dissociator Power Amplifier Control Unit Electronic Package RF Unit SHM: An Active Maser for Space

  12. SHM Physics Package

  13. SHM Parameters Measured Parameters • Temperature stabilization of the microwave cavity: <1mK • Active oscillation: power level of -104 dBm (specified: -105 dBm) • Measurement of the atomic quality factor via the cavity pulling effect: 1.5109 (specified: 1.5109) • Cavity quality factor: (35487 ±164) Hz • Measurement of the spin-exchange tuning point: 8741 Hz • Characterization of the maser signal vs B-field • Frequency instability without ACT as expected • Magnetic shielding factor: 2105

  14. The ACES Clock Signal Short term servo loop Locks PHARAO local oscillator to SHM ensuring a better short and mid-term stability Long term servo loop Corrects for SHM drifts providing the ACES clock signal with the long-term stability and accuracy PHARAO Stability of the ACES clock signal: - 310-15 at 300s (ISS pass) - 310-16 at 1 day - 110-16 at 10 days Accuracy: ~110-16

  15. FCDP Engineering Model

  16. 100 10 1 0,1 PHARAO -1 0 1 2 3 4 5 6 7 10 10 10 10 10 10 10 10 10 SHM MWL [ps] ) t ( x s t [s] ACES Microwave Link • Time stability • 0.3 ps over 300 s • 6 ps over 1 day • 23 ps over 10 days • Clock comparisons at the 10-17 level on an integration time of 1 day possible

  17. 100 MHz Clock I/F S-Tx Delay Lock Loop Antennas of the microwave link space segment tested in Compensated Compact Range (CCR) System Timing MWL Status

  18. ACES Operational Scenario Common View Comparisons • Comparison of up to 4 ground clocks simultaneously • Uncertainty below 1 ps per ISS pass (~ 300 s) • Mission Duration: 1.5 years up to 3 years • ISS Orbit Parameters: • Altitude: ~ 400 km • Inclination: ~ 51.6° • Period: 90 min • Link According to Orbit Characteristics: • Link duration: up to 400 seconds • Useful ISS passes: at least one per day • MWL Ground Terminals • Located at ground clock sites • Distributed worldwide Non-Common View Comparisons: • ACES clocks as fly wheel • Uncertainty below 2 ps over 1000 s and 20 ps over 1 day

  19. ACES Mission Objectives I

  20. ACES Mission Objectives II

  21. From the -wave to the optical domain • Fractional frequency instability at the quantum projection noise •   1Hz, limited by the interaction time (effect of gravity) • Nat  106, limited by cooling and trapping techniques, collisional shift, etc. • Solution: increase 0optical transition show a potential increase of 5 orders of magnitude • -wave fountain clocks: • Optical clocks: • Accuracy  theoretical studies foresee the possibility of reaching the 10-18 regime • Major difficulties: • Measurements of optical frequencies (frequency-comb generator) • Recoil and first order Doppler effects • Downconversion noise of the interrogation oscillator (Dick effect)

  22. Principle of Operation of Optical Clocks from S.A. Diddams et al., Science 293, 825 (2001)

  23. Optical clocks Microwave clocks , Ca Accuracy of the Atomic Time

  24. Clocks in Space

  25. Illustration taken from: http://perso.wanadoo.fr/alain.calloch/images/daumier.GIF

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