Atomic Clocks
Physical Seminar
- Quantum Optics and Nanophotonics Peter Deiml
20.05.2014
Table of contents
•
Why do we need an exact definition of time?
•
Current time standard
•
Spectroscopy
•
Ramsey-Spectroscopy
•
Caesium beam clock
•
(Laser Cooling)
•
Caesium fountain clock
•
Outlook: Optical Clock
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Why do we need an exact definition of time? [Bauch, 2003],[Bauch, 2012]
“The accurate measurement of time and frequency is vital to the success of many fields of science and
technology.” [Bauch, 2003]
Some scientific examples:
Some everyday examples:
• Other SI-units (e.g. meter)
• Global Positioning System
based upon the second
(GPS)
• Spectrum of atoms (QM,QED)
• Telecommunication
• „Proof“ of equivalence
• Supply of energy
principle, SR, GR (Hafele-Keating-/
Maryland-experiment)
• Gravitational waves
• Fine structure constant
Fig. 2: NAVSTAR
satellite [Wiki GPS, 2014]
Fig. 1: Hafele, Keating
& stewardess aboard
airplane with two
atomic clocks
[Wiki HKE, 2014]
constant?
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Current time standard
Definition of the second (1967)
„The second is the duration of 9192631770 periods of the radiation corresponding to the transition
between the two hyperfine levels of the ground state of the caesium 133 atom“
[BIPD, 2006]
• Why atomic properties?
• Why the Cs-133 atom?
• Why hyperfine levels?
• Why exactly 9192631770 periods of the
radiation?
→ value equals to ephimerises second
Quantum Optics and Nanophotonics
Fig. 3: Solar system with sun and the nine planets (not
true to scale) [SeaSky, 2014]
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Current time standard
Why atomic properties? [Bauch, 2012]
„ Zeit [ist] die Stellung des kleinen Zeigers meiner Uhr “ [Einstein, 1905]
• Every frame of reference has its own time
• Atomic properties determined by natural constants (in rest frame of
the atom)
Fig. 4: Spacetime in special relativity
Time determined by natural constants!
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[Wiki SR, 2014]
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Current time standard
Why the Cs-133 atom? [PTB]
• Small thermal velocity due to large mass
(later: Doppler effect → 0)
• Technology for measuring the resonance frequency was available in 1967
• The only natural isotope of caesium
• Only two hyperfine levels in the ground state
• Transition has small natural line width
• Small boiling point (670°C)
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Current time standard
Why hyperfine levels? [Audoin et al., 2005]
Quantum number configuration of the outermost
electron of Cs-133:
• No fine structure (J)
• Transition for time standard: F = 3 ↔ F = 4
Fig. 6: Cutting of the hyperfine structure of Cs-133
[Bauch, 2003]
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Spectroscopy
General idea
Investigation of the answer of atoms or molecules to a laserbeam
Perfect method for measurement of the second
Examples:
• Information about structure of stars
Fig. 7: UVES on the very large
telescope on Cerro Paranal
(Chile)
• Scientific applications: medicine (MRT),
[Wiki SpC, 2014]
[Wiki SpC, 2014]
chemistry, biology
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Fig. 8: Dispersion of
white light by a prism
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Spectroscopy
Broadening mechanisms [Meschede, 2007]
Natural line width:
Fig. 9:
spectrum of
low-pressure
mecury bulb
[Wiki NLW, 2014]
Doppler effect:
Fig. 10:
Gauß-Voigt
profile with
underlying
natural line width
[Meschede, 2007]
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Spectroscopy
Broadening mechanisms [Meschede, 2007]
Time-of-flight (TOF) broadening [Meschede, 2007]
Fig. 11: Scheme of spectroscopy experiment
[Wiki TOF, 2014]
Other broadening mechanisms [Audoin et al., 2006]
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Ramsey-Spectroscopy
Young‘s double slit (Position space):
Fig. 12: Scheme of Young‘s double slit [Wiki YDS, 2014]
Quantum Optics and Nanophotonics
Fig. 13: Distribution of intensity [Wiki YDS,2014]
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Ramsey-Spectroscopy
Fig. 15: See frame 11
Fig. 14: Scheme of Ramsey-spectroscopy
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Caesium beam clock
Caesium beam tube [Bauch, 2003],[Audoin et al., 2006]
• Analyzer deflects F = 4
atoms towards detector
Fig. 16: Scheme of the magnetically deflected caesium beam tube [Bauch, 2003]
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Caesium beam clock
The CS2 clock at the Physikalisch Technische Bundesanstalt (PTB)
Fig. 18: See frame 13
Fig. 17 : Vertical section of the vacuum chamber of PTB‘s primary clock CS2
[Bauch, 2003]
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Caesium beam clock
Function of Polarizer/Analyzer [Audoin et al., 2006]
Fig. 19: Energy of the hyperfine levels via the magentic flux density
[Audoin et al., 2006]
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Caesium beam clock
C field inside the cavity [Riehle, 2004]
Fig. 20: See frame 12
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Caesium beam clock
Frequency response of a caesium beam tube [Audoin et al., 2006]
Fig. 21: Scheme of the resonance of the central
part [Bauch, 2003]
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Caesium beam clock
Frequency response of a caesium beam tube [Audoin et al., 2006]
Fig. 22: See frame 17
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Laser cooling [Weyers et al., 1999]
Fig. 23: Order of laser beams, their
polarisation in an optical molasse
Fig. 24: Order of laser beams, their
polarisation in a magneto-optical trap
[Weyers et al., 1999]
[Weyers et al., 1999]
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Caesium fountain clock
General structure [Weyers et al., 1999]
• Charge of magneto-optical trap
• State-selection, Ramsey cavity and C-field analogeously to
caesium beam clock
• Difference: Preparation of F = 4 atoms
• Only one interaction zone is needed
• Different detection method with
lasers
Fig. 25: Simplified
setup of the
atomic fountain
clock [Wynands et
al., 2005]
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Caesium fountain clocks
Results of caesium fountain clock [Weyers et al., 1999]
Figure 21 (CSF1):
Fountain clocks more precise than beam clocks
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Outlook
Optical clocks
Fig. 27: Temporal development of
frequency uncertainty [Udem et al.,2009]
Optical clocks need the frequency comb technology
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Take-home message
Current time standard:
•
Exact definition is needed
Caesium beam/fountain clock:
•
Definition of the second & its justification
•
General setup
•
Functional principle and task of all
components
Spectroscopy:
•
Method for realization of time standard
•
Broadening mechanisms
•
Frequency response signal
•
Fountain clock more precise than beam clock
Ramsey-Spectroscopy:
Optical clocks:
•
Double slit in time space
•
More precise than caesium clocks
•
Strong analogy to Young‘s double slit in
•
Frequency comb technology is nessecary
position space
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Hallo
Thank you for your attention
and
feel free to ask questions!
(after the next presentation  )
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Appendix
Detection and measurement of transition [Weyers et al., 1999]
• Measurement of flourescence by two detectors (photodiodes)
Fig. 20: Scheme of the detection zone [Weyers et al., 1999]
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References
[Audoin et al., 2006]
[PTB 1]
Audoin C., Guinot B., The measurement of time, Cambridge University Press,
2001
Bauch A., Caesium Atomic Clocks: Function, Performance and Applications, Measurement
Science and Technology 14, 1159-1173 (2003)
Bauch A., Zeitmessung in der PTB, PTB Mitteilungen 122, 2012
Bauch A., Fischer B., Heindorff T., Schröder R., Performance of the PTB reconstructed
primary clock CS1 and an estimate of ist current uncertainty, Metrologia 35, 829-845, 1998
Bureau international des poids et mesures, Organisation interfouvernementale de la
Convention du Mètre. Le Système international d‘unités, 8e édtion, 2006
Demtröder, W., Experimentalphysik 3, Atome, Moleküle und Festkörper, 3. Auflage,
Springer Verlag, Berlin, Heidelberg, New York, 2005
Einstein A., Zur Elektrodynamik bewegter Körper, Annalen der Physik und Chemie. 17, S.
891 – 921, 1905
Fließbach T., Allgemeine Relativitätstheorie, Spektrum, 2006
Meschede D., Optics, Light and Lasers, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim,
2007
Physikalisch-Technische Bundesanstalt, Wie funktioniert eine Atomuhr?
[PTB 2]
Physikalisch-Technische Bundesanstalt, Optische Atomuhren
[Bauch, 2003 ]
[Bauch, 2012]
[Bauch et al., 1998]
[BIPD, 2006]
[Demtröder, 2005]
[Einstein, 1905]
[Fließbach, 2006]
[Meschede, 2007]
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References
[Riehle, 2004]
[Udem et al., 2009]
[Weyers et al., 1999]
[Wynands et al., 2005]
Riehle F. Frequency Standards: Basics and Applications, Wiley-VCH Verlag GmbH & Co.
KGaA, Weinheim, 2006
Udem T., Holzwarth R., Hänsch T. W., Femtosecond optical frequency combs, European
Journal of Physics – Special Topis 172,69-79, 2009
Weyers S., Griebsch D., Hübner U., Schröder R., Tamm C., Bauch A., Die neue
Caesiumfontäne der PTB, PTB-Mitteilungen 109, 483-491, 1999
Wynands R., Weyers S., Atomic fountain clocks, Metrologia 42, 64-79, 2005
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Web references
[Wiki SR, 2014]
http://en.wikipedia.org/wiki/Special_relativity, 02.05.2014
[Wiki GPS, 2014] http://de.wikipedia.org/wiki/Global_Positioning_System, 02.05.2014
[Wiki SC, 2014]
http://de.wikipedia.org/wiki/Bahnhofsuhr, 02.05.2014
[Wiki MBD, 2014] http://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution, 02.05.2014
[Wiki SpC, 2014] http://en.wikipedia.org/wiki/Spectroscopy, 02.05.2014
[Wiki NLW, 2014] http://de.wikipedia.org/wiki/Linienbreite, 02.05.2014
[Wiki TOF, 2014] http://de.wikipedia.org/wiki/Flugzeitverbreiterung, 02.05.2014
[Wiki YDS, 2014] http://de.wikipedia.org/wiki/Doppelspaltexperiment, 09.05.2014
[SeaSky, 2014]
http://www.seasky.org/solar-system/solar-system.html, 18.05.2014
[Spiegel, 2013]
http://www.spiegel.de/wissenschaft/technik/zeitmessung-physiker-bauen-zuverlaessigste-uhraller-zeiten-a-917409.html, 18.05.2014
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