Optical Clocks at PTB

Transcription

1 Optical Clocks at PTB Outline Introduction to optical clocks An optical frequency standard with Ca atoms Improved reference cavity Yb + Ion Clock Sr optical lattice clock Optical frequency measurements European Australian Workshop on Quantum-Atom Optics, February 26 Physikalisch-Technische Bundesanstalt

2 Principle of Clocks Atome, neutral single absorber Moleküle atoms ion oder Ionen Oszillator oscillator Laser Detektor detector ν S ν ν fs frequency comb Regelungselektronik servo - electronics Fehlersignal error ds dν ν ν Absorptions- absorption signal

3 Why better clocks? Generation of more stable time scales secondary representations of the second future better definition of the second Tests of fundamental theories: General Relativity Cosmology Constance of fundamental constants Navigation Deep-space navigation Pioneer anomaly

4 Pioneer Anomaly unexplained acceleration α Pioneer = - (8.74 ± 1.33) 1-1 m/s 2

5 Laser Cooling of Calcium first stage: 4p3d 1 D 2 T 3 mk 1 P nm Quenchlaser quench laser 453 nm second stage: quench-cooling: T 1 µk Kühlübergang cooling 423 nm, 35 MHz 1 S 4s3d 1 D 2 3 P 1 Uhrenübergang clock transition nm, nm32 Hz 37 Hz count Zählrate (arb. (w. E.) units) v =,11 m/s v = 1,63 m/s Geschwindigkeit velocity (cm/s) (cm/s) T. Binnewies et al., PRL 87, (21)

6 Ca: Clock transition and cooling second stage cooling 4p3d 1 D 2 1 P 1 Quench 453 nm 1 S 3 P 1 Clock 657 nm 37 Hz T T T Freely expanding cloud of ultra cold atoms for atom-interferometry z N = atoms n = cm -3 T = 1 µk T. Binnewies et al., PRL 87, (21) t

7 Cold and Ultracold Atom Interferences 3mK 1 µk,6 Fluoreszenz 657 nm Fluorescence 657 nm Doppler width 3 MHz ν (MHz) > p e>,4,2, -,9 -,6 -,3,,3,6,9 Fourier width 1 MHz > ν (MHz) Doppler width.2 MHz

8 Optical frequency measurement of calcium Ca-Frequencystandard 456 THz Comparison frequency chain / frequency comb Primary Standard Cs-Fountain 9.2 GHz ν Ca Hz (Hz) NIST NIST 1997 Sep ' Jun '1 Oct '1 Oct '3 May ' PTB October 23 n Ca = Hz ± 5.5 Hz u y = Calcium is still the best neutral atom clock u y ~1-15 is possible but motion sets a limit

9 Uncertainty - Stability good clock: small uncertainty high stability small uncertainty low stability high stability low uncertainty Allan Variance: σ ( ν ν ) y ( τ ) = 2 i i+ 1 ν with ν i 1 = τ t + τ i t i ν (t) dt

10 Stability Quantum Projection Noise Limit: After the interrogation the number of excited atoms N e is measured i.e. the quantum state ψ is projected to either the state e> or g>. Ne N p e = cg g + c 2 = σ N = N p (1 p ) e e e e e 1 p e e> g> σ ( τ ) y ν ν T C N τ Itano et al., PRA 47,3554 (1993) T C : cycle time.5 ν ν ν Cs atoms, ν = 9.2 GHz, ν = 1 Hz : σ y (τ) ~ τ -1/2 Single Yb ion, λ = 436 nm, ν = 3.1 Hz: σ y (τ) ~ τ -1/2 1 7 Ca atoms, λ = 657 nm, ν = 4 Hz: σ y (τ) ~ τ -1/2

11 Interrogation Laser λ/4 to the Ca experiment AOM PBS phase modulator single mode fiber ECDL laser diode PZT mirror EOM Faraday isolator etalon grating Pol. Pol. ~ oscillator 1 MHz mixer vibration-isolation stage loop filter ULE resonator vacuum chamber PDHdetector Faraday isolator BS Pol. RAM-detector Resonance frequencies:.7 Hz vertical,.6 Hz horizontal H. Stoehr, F. Mensing, J, Helmcke, U. Sterr, Opt. Lett. March 23

12 Laser Linewidth relative optical power Hz FWHM resolution BW: 1 Hz acquisiton time 4 s g k /g S ν 1/2 (Hz/Hz 1/2 ) T c =3 ms T probe = 1 ms vibrations ν(hz) power spectrum of the beat f (Hz) spectral density of frequency noise weighting function laser linewidth 1 Hz, drift.6 Hz/s Dick effect: σ 2 ( τ ) = τ 2 y k = 1 S y ( kf c ) g g k 2 Present stability is imited by Dick effect because of the poor duty cycle to σ(τ) = τ -1/2

13 previous cavity mount Finite-Element calculations: point support on viton pieces from below z a y (m/s 2 ) khz/ms u z m 2 1 m a = 1 m/s 2 deformations magnified by mirror ν beat (khz) support points t (s)

14 new cavity mount The spacer is held in its horizontal symmetry plane -.1 nm uz.1 nm a = 1 m/s 2 deformations magnified by 1 7 see poster by Tatiana Nazarova z a y (m/s 2 ) ν beat (khz). support points -.2 mirror khz/ms -2 blind holes improvement by factor t (s)

15 171 Yb + Single-Ion Frequency Standard Ekkehard Peik, Christian Tamm 2 P 1/2 371 nm cooling and detection τ ~ 5 ms 436 nm 2 D 3/2 2 S 1/2 F=1 F= clock transition: 2 S 1/2-2 D 3/2 λ = 436 nm, ν = 3.1 Hz σ y (min) ~ s -1/2 Quantum jump probability Hz -4 4 Detuning at nm (Hz)

16 Frequency comparison between two ions Frequencies agree to 3.8(6.1)â1-16 (similar to best results of Cs-clocks) T. Schneider, E. Peik, Chr. Tamm, Phys. Rev. Lett. 94, 2381 (25) Instability of difference frequency: s y (1 s)= (similar to best results of cold atoms) E. Peik, T. Schneider, Chr. Tamm, J. Phys. B. 39, 145 (26)

17 Frequency Messurement of the Yb + -clock f(yb) Hz Date of Measurement (MJD) ν(yb + )= (2.2) Hz Cotributions to uncertainty budget of the measurements in 25: u A =.4 Hz (continuous measurement time of up to 36 h) u B (Cs)=1.82 Hz ( π/3π -problem) u B (Yb + )=1.5 Hz (Quadrupole-, Black-body-Stark-shift, line profile, influence of the trap fields)

18 Optical Lattice Clock Earth alkali elements Mg, Ca, Sr and Yb, Hg have metastable 3 P state Strontium accessible by 1 photon transition in isotopes with nuclear spin I ν ~ mhz in most abundant isotopes with I = transitions get allowed in magnetic field ν ~ µhz with B ~ 1 mt magic wavelengths dipole traps efficient cooling possible Cooling Cooling 698 nm Magic Wavelength Clock - no net light shift 1 7 neutral atoms estimated uncertainty u y < 1-16

19 Strontium Setup oven 2D deflection molasses Zeeman slower MOT chamber Sr-Atoms T = 5 mk loading time 1 ms

20 Optical Frequency Comb time domain: fs-laser with repetition frequency f rep 1/frep t frequency domain: comb of frequencies ν(m) ν(2m) 2ν(m) ν ceo f rep self-referencing to measure ν ceo ν(m) = ν ceo + m f rep ν ceo = 2ν(m) - ν(2m) ν(2m) = ν ceo + 2m f rep

21 fs Frequency Combs Ti:sapphire comb broad-band for calibration of lasers 633 nm, 532 nm.. Er:fiber comb frequency devider for optical clock comparison of Yb+ Ca Sr Universität Konstanz Fachbereich Physik

22 drift of an optical cavity For details: see poster by Gesine Grosche

23 optical clock ensemble atoms in an optical lattice short-term stability pendulum frequency comb time optical cavities pendulum clockwork accuracy

24 Conclusion Calcium clock vibrationally insensitive reference cavity relative frequency uncertainty Yb clock relative uncertainty Strontium lattice clock Reliable fiber based femtosecond comb Future: Uncertainty 1-17 with ions and atoms in lattice Clock with instability < 1-16 in one second New area at <1-16 : Gravitational red shift, Constancy of constants Thermal noise

25 Thanks to: Ca standard: Tatiana Nazarova Felix Vogt Christian Lisdat (U. Hannover) Christophe Grain Carsten Degenhard (now Aachen) Hardo Stoehr (now Lübeck) Sr standard: Thomas Legero Sundar Raaj Paul-Eric Pottie (now Paris) Fritz Riehle U.S. SFB 47: Quantum-limited measurements with photons, atoms and molecules Frequency measurements: Gesine Grosche Harald Schnatz Burghardt Lipphardt Yb + single ion: Christian Tamm Ekkehard Peik Tobias Schneider Funding: DFG EU CAUAC SFB 47