Optical clock measurements beyond the geodetic limit

Transcription

1 Optical clock measurements beyond the geodetic limit Andrew D. Ludlow Optical Frequency Measurements Group National Institute of Standards and Technology Boulder, CO USA

2 Talk outline Atomic clock figures of merit Yb optical lattice clocks at NIST General description Uncertainty evaluation Clock stability at long times Measurements between the Yb clocks Optical frequency ratio measurements Towards portability

3 Figures of merit So how accurate is your clock?

4 Systematic Uncertainty UNCERTAINTY IN REALIZING UNPERTURBED EIGENFREQUENCY OF ATOM characterized with an uncertainty evaluation electric and magnetic fields, atomic collisions, observational and relativistic effects,

5 (In)stability HOW MUCH THE TIMEBASE VARIES OVER TIME sets the statistical precision afforded by the clock timebase averaged over longer times generally more stable

6 Reproducibility HOW WELL THE TIMEBASES OF TWO SIMILAR STANDARDS AGREE should be determined by systematic uncertainty and stability

7 Accuracy? Accuracy Systematic Uncertainty? Accuracy Syst. Uncertainty + Stability (rss)? Accuracy Reproducibility?

8 the Yb optical lattice clock ac Stark shift [MHz] ~759 nm 3 P 0 1 S H. Katori et al., PRL 91, (2003) Wavelength [nm]

9 the Yb optical lattice clock Brown et al., PRL 119, (2017)

10 the Yb optical lattice clock

11 the Yb optical lattice clock 3 P 0 clock transition 1 S 0

12 Systematic Uncertainty UNCERTAINTY IN REALIZING UNPERTURBED EIGENFREQUENCY OF ATOM characterized with an uncertainty evaluation electric and magnetic fields, atomic collisions, observational and relativistic effects,

13 Yb clock uncertainty budget Yb-1 (x10-18 ) Yb-2 (x10-18 ) Systematic effects Shift Uncertainty Shift Uncertainty BBR Stark Lattice statistical Lattice model Lattice traveling wave 0 < Second-order Zeeman Spin polarization purity <0.1 Cold collision Background gas collision DC Stark Probe AC Stark First-order Doppler Second-order Doppler 0 <0.1 0 <0.1 Tunnelling 0 < <0.01 Servo error Line Pulling 0 <0.1 0 <0.1 AO Phase Chirp (OFS) Total W. McGrew et al., in preparation

14 Radiative thermal environment Yb

15 Blackbody Blackbody Stark shift radiation shift Beloy et al, PRL (2014)

16 Blackbody Stark shift Beloy et al, PRL (2014) Beloy et al, in preparation

17 DC Stark shift x Shift (FF) -1.0x x Shift(Hz) -2.0x x Voltage (V) Direction uncertainty X Y Z Total Beloy et al, in preparation

18 (In)stability HOW MUCH THE TIMEBASE VARIES OVER TIME sets the statistical precision afforded by the clock timebase averaged over longer times generally more stable

19 Measuring stability M. Schioppo et al., Nat. Photonics (2017)

20 Measuring stability M. Schioppo et al., Nat. Photonics (2017)

21 Downsampling of Optical Noise sensitivity function time (s)

22 Even better stability: zero dead time Yb-1 Yb-2

23 Stability: zero dead time Yb clock M. Schioppo et al., Nat. Photonics (2017)

24 Limited by optical aliasing (Dick effect) Instability at 1 second M. Schioppo et al., Nat. Photonics (2017)

25 Stability at long times Short term stability detection and laser frequency noise Long term stability drifting systematics

26 Stability at long times W. McGrew et al., in preparation

27 Reproducibility HOW WELL THE TIMEBASES OF TWO SIMILAR STANDARDS AGREE should be determined by systematic uncertainty and stability

28 Reproducibility series of measurements to assess agreement between two Yb lattice clocks frequency measurements preceded by a series of parameter checks to ensure clocks expected to be in compliance with uncertainty evaluation blinding protocol: relative frequency difference between the two systems is not known until the end of measurement day.

29 Reproducibility: geodetic perspective Δh 6 cm 6 x 10-18

30 Interspecies optical clock comparisons

31 Intercontinental: ACES ISS mission Improved test of GR redshift Special relativity tests (isotropy of the speed of light) Fine structure constant variation through ground clock comparisons Ground clock comparisons at the level

32 Optical clock comparisons Optical frequency ratio measurements: Yb, Al +, Sr Collaboration: NIST Ion Storage, JILA Sr, NIST OFM, NIST FSA

33 Optical Two-Way Time and Frequency Transfer Bern ISSI, March 20, 2018 Nathan R. Newbury, Jean-Daniel Deschênes, Laura Sinclair, William Swann, Hugo Bergeron, Issac Khader, Esther Baumann,Martha Bodine NIST, Boulder, CO, USA OctoSig, Québec, QC, Canada the following 12 slides from Newbury et al.

34 Optical Two-Way Time and Frequency Transfer (TWTFT) Optical clocks/oscillators have femtosecond jitter & extreme frequency accuracy RF/Microwave links cannot transfer these signals faithfully need an Optical link for Optical clocks/oscillators Fiber optic links work but are not always (or even often) available Goal: Method for fs-level transfer of optical clock/oscillator signals over free-space Coherent Exchange of Frequency Comb Pulses Master optical clock/oscillator Cavity-stabilized laser or full atomic clock Remote clock / oscillator optical or rf

35 Why is this hard? Turbulence, platform motion Clock Frequency Comb Frequency Comb Clock 1) Amplitude noise & signal loss From turbulence (scintillation & beam wander) From obstructions & platform motion Well-known from free-space optical communications 2) Phase noise (time-of-flight variations) From turbulence ( piston effect ) From platform motion Relative velocity of 3 nm/sec v/c < Relative motion of 300 nm 1 femtosecond

36 Two-Way Time Transfer: Basic Concept Site A Site B t A =0 t B =0 Timer Timer t B A =T link - t AB t A B =T link + t AB t AB Clock Time Offset Requires a Reciprocal Link A single-mode optical link is reciprocal!

37 Two-Way Time Transfer + Feedback Synchronization Site A feedback Site B Timer Timer t B A t A B t AB Real-time calculation

38 Two-Way Time Transfer: With Combs Site A Site B Timer Timer t B A =T link - t AB t A B =T link + t AB Comb timing is at femtosecond level! But timing information lost in photodetection still picosecond level timing

39 Coarse Two-way & Comms Comb-based Synchronization CW Laser Coherent TX/RX System Timing Exchange CW Laser Coherent TX/RX Coarse Two-way & Comms Controller Synch. T Equation Hz Feedback BW Remote Comb Comb-based timing measurement Clock Output Clock Output Comb-based timing measurement Transfer Comb Master Comb Controller Three signals between sites: Phase modulated cw light for coarse two-way timing Comb light for fine two-way timing Coherent communication (to close the loop) Plus full calibration of each terminal delays for absolute time

40 4 km Turbulent Air Path

41 From 4 km to 11.6 km: NIST to Valmont Butte Valmont Butte current link 1 km NIST View from NIST Valmont Butte

42 Carrier-Phase OTWTFT Comb fiber link Oscillator A Oscillator B Θ A Two-way carrier-phase extraction Θ B t A Relative timing t B

43 Carrier Phase OTWTFT Allows Frequency Comparisons at sec Fractional Frequency Instability (Mod. Allan) Carrier phase OTWTFT Previous OTWTFT (pulse envelope only) 10X-30X improvement to 1 second Averaging Time (s)

44 Carrier Phase OTWTFT: Same improvement at higher turbulence levels Fractional Frequency Instability (Mod. Allan) carrierphase OTWTFT Previous OTWTFT 1% fades (low turbulence) 26% fades (high turbulence) Averaging Time (s)

45 Optical Two-Way Time Transfer: Summ Remote site Femtosecond Clock Network We can synchronize to femtoseconds: Over strong turbulence Through dropouts At velocities up to 50 mph with no degradation To 1 sec quartz oscillator or optical cavity Master Optical Oscillator/Clock Future work Longer distances Networks Atomic clock to atomic clock Higher velocities J. D. Deschenes et al., Physical Review X, (2016) L. Sinclair et al., Applied Physics Letters, 109, (2016) H. Bergeron et al, Optica, (2016) L. Sinclair et al., Physical Review Lett, 120, (2018)

46 Compact cold atom sources

47 Compact cold atom sources Collaboration with E. Riis, A. Arnold, P. Griffin et al., Univ. of Strathclyde Nshii et al., Nature Nanotechnology 8, (2013)

48 Perspective With additional development OLCs could eventually reach low total (statistical and systematic) uncertainty mm level geodetic accuracy? OLCs will reach stability at 1 second - Cryo-cavity lasers - Large atom numbers - Spin squeezing - Zero dead time D.G. Matei et al., Phys. Rev. Lett. 118,

49 Acknowledgments W. McGrew X. Zhang R. Fasano D. Nicolodi K. Beloy R. Brown M. Schioppo N. Hinkley T. H. Yoon N. Phillips G. Milani T. Fortier C. W. Oates S. Diddams T. Fortier H. Leopardi postdoc position available Fund. Phys. PECASE NIST Gebbie Laboratory