Cold cesium frequency standard

• Research unit: METAS
• Project number: 216.99.01

Key words (German)

Internationales Einheitensystem, Sekundenrealisierung, Zeit- und Frequenznormal, Laserkühlung

Key words (English)

International system of units, Realization of the second, time and frequency standard, laser cooling, cesium fountain

Short description (German)

Die Sekunde ist die mit Abstand am genausten realisierte Einheit im SI-System. Die weltum-spannenden Kommunikations- und satellitengestützten Navigationssysteme sind die direkten Nutzniesser dieser Genauigkeit. Ihre zukünftige Entwicklung ist mit dem Fortschritt auf dem Gebiet der Frequenz- und Zeitmetrologie eng verknüpft. Die Realisierung der Sekunde basiert auf einem atomaren Übergang im Cäsium-Atom, dessen Frequenz in einem Frequenznormal auf die Frequenz eines externen Oszillators übertragen wird.
Die Genauigkeit von konventionellen Cäsium-Normalen wird durch die thermische Bewe-gung der Atome begrenzt. Mit der Entwicklung der Laserkühltechnik ist es möglich geworden, thermische Atome einzufangen und beinahe auf den absoluten Nullpunkt abzukühlen. Da sich kalte und damit langsame Atome viel länger beobachten lassen, kann mit dieser Technik die Genauigkeit von Frequenznormalen stark verbessert werden.
Das Observatorium Neuenburg baut zusammen mit dem METAS ein Frequenznormal, das auf einem kontinuierlichen Strahl von lasergekühlten Cäsiumatomen basiert.

Short description (English)

The second is by far the most accurately realised unit in the SI System. The world-wide communications and satellite-supported navigation systems are the direct beneficiaries of this precision. Any further development of theseis systems in the future is dependent on progress in theis field of frequency and time metrology.
The realisation of the second is achieved by the use of so-called cesium atomic clocks. Their accuracy is limited by the thermal movement of the atoms. With the help of lasers, it has become possible to capture thermal atoms and cool them to very close to the absolute zero point. Since cold and therefore more slowly moving atoms can be observed much more accurately, this technology allows a considerable improvement to be achieved in the accuracy of frequency standards.
The Neuenburg Observatorium, in conjunction with the METAS, is building a frequency standard which is based on a continuous fountain of laser-cooled cesium atoms.

Project aims (German)

Das EAM entwickelt in Zusammenarbeit mit dem Observatorium Neunenburg ein Primärnormal für Zeit und Frequenz auf der Basis eines kontinuierlichen Strahls von lasergekühlten Cäsium-Atomen. Das Ziel für die relative Frequenzgenauigkeit liegt bei 10-15, dasjenige für die Kurzzeitstabilität bei 7•10-14. Das neue Normal soll nach seiner Vollendung einen bedeutenden Beitrag an die Realisierung der Sekunde und der Atomzeitskala TAI leisten.

Project aims (English)

A primary frequency standard based on a continuous beam of laser cooled cesium atoms is developed. The accuracy goal for the frequency is 10-15 with a short term stability of 7•10-14. At the end of its development, the new standard should make a significant contribution to the realization of the second and the international atomic time scale TAI.

Abstract (German)

In einer Zusammenarbeit zwischen METAS und dem Observatorium Neuenburg wurde ein Primärfrequenznormal entwickelt. Als weltweit einziges Instrument basiert die Fontaine Continue au CéSium (FOCS-1) auf einem kontinuierlichen Strahl lasergekühlter Cäsiumatome. Die Kontinuität des Atomstrahles führt zu wichtigen metrologischen Vorteilen, zumal sich das Unsicherheitenbudget anders zusammensetzt als bei den sonst üblichen gepulsten Cäsium-Springbrunnen anderer Metrologieinstitute. Die zur Zeit beste gemessene Kurzzeitinstabilität mit FOCS-1 beträgt 2.5·10-13 in einer Sekunde, etwas mehr als einen Faktor 3 höher als ursprünglich anvisiert. Die relative Frequenzgenauigkeit wurde noch nicht vollständig evaluiert. Testmessungen zeigen jedoch, dass das anvisierte Niveau von 10-15 mit dem Gerät erreicht werden sollte.
Da alle Untersysteme des Aufbaus aber funktionieren und zumindest auch das Ziel der Genauigkeit in Reichweite ist, kann der Grad der Zielerreichung des Projektes mit 95% angegeben werden.

Abstract (English)

In a collaboration with the Observatory of Neuchatel, a primary frequency standard was designed, assembled and tested. As the only device world-wide, this instrument, labeled FOCS-1, is based on a continuous beam of laser cooled cesium atoms. The continuity of the cold atomic beam yields important metrological advantages, since the uncertainty budget builds up differently than with pulsed fountains in operation in other National Metrological Institutes (NMIs). At present, the best measured short term instability of FOCS-1 is 2.5·10-13 in one second, roughly a factor of 3 higher than initially planned. As for the accuracy, the ultimate goal of 10-15 has not yet been tested. However, all test measurements conducted so far indicate that the design is compatible with the initial accuracy goal.
All sub-systems of the FOCS-1 work properly and at the accuracy goal is within reach. Therefore, the degree of achievement of the goals of the project can be indicated as 95 %.

Transfer and application (German)

Mit FOCS-1 verfügt METAS, und somit die Schweiz, erstmals über ein Primärfrequenznormal.
Mit diesem Instrument kann zum einen in Zukunft das Ensemble der kommerziellen Atomuhren am METAS kalibriert werden. Dies vereinfacht die Rückverfolgbarkeitskette für Kalibrierungen wesentlich, da mit FOCS-1 die SI-Sekunde direkt am METAS realisiert wird. Die für eine Kalibrierung der Frequenz des Ensembles nötigen Instrumente sind bereits vorhanden.
Zum andern wird FOCS-1 aber auch zur Realisierung der SI-Basiseinheit Sekunde beitragen und dem Zeit- und Frequenzlabor von METAS zu einem höheren Stellenwert im internationalen Vergleich verhelfen. Zu diesem Zweck wurden parallel zum vorliegenden Projekt zwei Frequenztransferprojekte (GeTT und TWSTFT) vorangetrieben. Über diese Hilfsmittel wird FOCS-1 in Zukunft mit Primärfrequenznormalen anderer Nationaler Metrologieinstitute verglichen.

Transfer and application (English)

FOCS-1 is the first primary frequency standard of METAS, and thus of Switzerland. With this device it will be possible to calibrate the ensemble of commercial atomic clocks operated at METAS. This will facilitate the traceability chain for calibrations, since FOCS-1 will realize the SI-second at METAS. The equipment necessary for the calibration of the ensemble of atomic clocks is already operational in the laboratory.
In addition, FOCS-1 shall also contribute to the realisation of the SI-second, thereby improving the international visibility of METAS in this domain. To integrate results of FOCS-1 in the international network, two other projects are presently conducted (GeTT and TWSTFT) to build up frequency transfer facilities at METAS. By these means, FOCS-1 shall in the near future be compared with primary frequency standards of other NMIs.

Publications / Results (German)

Artikel in Fachzeitschriften und Konferenzbeiträge :
- A Joyet, N Castagna, P Thomann, G Dudle, C Mandache, T Acsente, Metrological Aspects of the ON-METAS continuous fountain standard, Proc. of the joint meeting IEEE-FCS/17th EFTF, Tampa, Florida, 2003
- A Joyet, N Castagna, G Mileti, P Thomann, C Mandache, T Acsente, G Dudle, Preliminary evaluation of the ON-METAS continuous fountain, 16th European frequency and time forum, St Petersburg, Russia, 2002
- A Joyet, G Mileti, P Thomann, G Dudle, Stability and accuracy results with the ON/METAS continuous cesium fountain, Conference Digest CPEM, Ottawa, Canada, 2002
- G Dudle, A Joyet, P Berthoud, G Mileti, P Thomann, First results with a cold cesium continuous fountain resonator, IEEE Trans. IM 50, 510 - 514, 2001
- A Joyet, G Mileti, P Thomann, G Dudle, Recent developments on the ON/METAS continuous Cs fountain standard, Proc. 15th European frequency and time forum, Neuchâtel, Switzerland, 72 - 76, 2001
- A Joyet, G Mileti, P Thomann, G Dudle, Continuous fountain Cs standard: stability and accuracy issues, Proc. 6th symposium on freq. stand & metrology, St. Andrews, Scotland, 273 - 280, 2001
- A Joyet, G Mileti, G Dudle, P Thomann, Theoretical Study of the Dick Effect in a Continuously Operated Ramsey Resonator, IEEE Trans. IM 50, 150 - 156, 2001
- G. Dudle, G. Mileti, A. Joyet, E. Fretel, P. Berthoud, P. Thomann; An alternative cold cesium frequency standard: the continuous fountain; IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 47, no. 2; pp. 438-442; 2000.
- G. Mileti, A. Joyet, P. Thomann, G. Dudle; Development of the ON/OFMET continuous Cs fountain standard: a progress report; 14th European frequency and time forum, 14.-16. March 2000, Torino.
- A. Joyet, G. Mileti, P. Thomann, G. Dudle; Theoretical study of the Dick effect in a continuously operated Ramsey resonator; 14th European frequency and time forum, 14.-16. March 2000, Torino.
- P. Berthoud, E. Fretel, A. Joyet, G. Dudle, P. Thomann; Towards a primary frequency standard based on a continuous fountain of laser-cooled cesium atoms; IEEE Trans. Instrum. Meas.; IM-48; 516-519; 1999.
- Valentin, N. Dimarcq, E. Fretel, A. Joyet, P. Thomann, G. Dudle; Numerical simulations of atomic behaviour for several configurations of cold cesium atoms; 13th European Time and Frequency Forum, Besancon; Proc.; 1999.
- G. Dudle, A. Joyet, E. Fretel, P. Berthoud, P. Thomann; An alternative cold cesium frequency standard: the continuous fountain; 13th European Time and Frequency Forum, Besancon; Proc.; 1999.
- P. Berthoud, A. Joyet, G. Dudle, N. Sagna and P. Thomann; A continuous beam of slow, cold cesium atoms magnetically extracted from a 2D magneto-optical trap; Europhys. Lett. ; 41(2); 141-146; 1998.
- Dudle, N. Sagna, P. Berthoud and P. Thomann; Anisotropic magneto-optical trapping of atoms: capture efficiency and induced drift velocities; J. Phys. B; 29; 4659-4673; 1996.
- N. Sagna, G. Dudle and P. Thomann; The capture process in spherical magneto-optical traps: experiment and 1D magnetic field models; J. Phys. B ; 29; 3213-3224; 1995. 

Publications / Results (English)

Publications in scientific journals and conference proceedings:
- A Joyet, N Castagna, P Thomann, G Dudle, C Mandache, T Acsente, Metrological Aspects of the ON-METAS continuous fountain standard, Proc. of the joint meeting IEEE-FCS/17th EFTF, Tampa, Florida, 2003
- A Joyet, N Castagna, G Mileti, P Thomann, C Mandache, T Acsente, G Dudle, Preliminary evaluation of the ON-METAS continuous fountain, 16th European frequency and time forum, St Petersburg, Russia, 2002
- A Joyet, G Mileti, P Thomann, G Dudle, Stability and accuracy results with the ON/METAS continuous cesium fountain, Conference Digest CPEM, Ottawa, Canada, 2002
- G Dudle, A Joyet, P Berthoud, G Mileti, P Thomann, First results with a cold cesium continuous fountain resonator, IEEE Trans. IM 50, 510 - 514, 2001
- A Joyet, G Mileti, P Thomann, G Dudle, Recent developments on the ON/METAS continuous Cs fountain standard, Proc. 15th European frequency and time forum, Neuchâtel, Switzerland, 72 - 76, 2001
- A Joyet, G Mileti, P Thomann, G Dudle, Continuous fountain Cs standard: stability and accuracy issues, Proc. 6th symposium on freq. stand & metrology, St. Andrews, Scotland, 273 - 280, 2001
- A Joyet, G Mileti, G Dudle, P Thomann, Theoretical Study of the Dick Effect in a Continuously Operated Ramsey Resonator, IEEE Trans. IM 50, 150 - 156, 2001
- G. Dudle, G. Mileti, A. Joyet, E. Fretel, P. Berthoud, P. Thomann; An alternative cold cesium frequency standard: the continuous fountain; IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 47, no. 2; pp. 438-442; 2000.
- G. Mileti, A. Joyet, P. Thomann, G. Dudle; Development of the ON/OFMET continuous Cs fountain standard: a progress report; 14th European frequency and time forum, 14.-16. March 2000, Torino.
- A. Joyet, G. Mileti, P. Thomann, G. Dudle; Theoretical study of the Dick effect in a continuously operated Ramsey resonator; 14th European frequency and time forum, 14.-16. March 2000, Torino.
- P. Berthoud, E. Fretel, A. Joyet, G. Dudle, P. Thomann; Towards a primary frequency standard based on a continuous fountain of laser-cooled cesium atoms; IEEE Trans. Instrum. Meas.; IM-48; 516-519; 1999.
- Valentin, N. Dimarcq, E. Fretel, A. Joyet, P. Thomann, G. Dudle; Numerical simulations of atomic behaviour for several configurations of cold cesium atoms; 13th European Time and Frequency Forum, Besancon; Proc.; 1999.
- G. Dudle, A. Joyet, E. Fretel, P. Berthoud, P. Thomann; An alternative cold cesium frequency standard: the continuous fountain; 13th European Time and Frequency Forum, Besancon; Proc.; 1999.
- P. Berthoud, A. Joyet, G. Dudle, N. Sagna and P. Thomann; A continuous beam of slow, cold cesium atoms magnetically extracted from a 2D magneto-optical trap; Europhys. Lett. ; 41(2); 141-146; 1998.
- Dudle, N. Sagna, P. Berthoud and P. Thomann; Anisotropic magneto-optical trapping of atoms: capture efficiency and induced drift velocities; J. Phys. B; 29; 4659-4673; 1996.
- N. Sagna, G. Dudle and P. Thomann; The capture process in spherical magneto-optical traps: experiment and 1D magnetic field models; J. Phys. B ; 29; 3213-3224; 1995.