LKB - Ultracold Fermi Gases

PHARAO/ACES

LKB Permanent Members
Christophe Salomon
Christine Guerlin

SYRTE Permanent Members
Philippe Laurent
Peter Wolf
Frederic Meynadier
Pacôme Delva
Christophe Leponcin-Lafitte

SYRTE Students
Hélène Pihan Le Bars (PhD)
Etienne Savalle (M1 student)

Selected Publications

Microwave lensing frequency shift of the PHARAO laser-cooled microgravity atomic clock
P. Peterman, K. Gibble, P. Laurent, C. Salomon
Metrologia 53, 899, (2016)

The ACES /PHARAO space mission
P. Laurent, D. Massonnet, L. Cacciapuoti, C. Salomon
Comptes-Rendus Acad. Sciences, Paris, 540 (2015)

Testing Lorentz symmetry with planetary orbital dynamics
A. Hees, Q. G. Bailey, C. Le Poncin-Lafitte,A. Bourgoin, A. Rivoldini, B. Lamine, F. Meynadier, C. Guerlin, and P. Wolf
PRD 92, 064049 (2015)

Some fundamental physics experiments using atomic clocks and sensors
C. Guerlin, and P. Delva, P. Wolf
C.R. Physique 16, 565, (2015)

PHARAO : le premier étalon primaire de fréquence à atomes froids spatial
P. Laurent et al.
REVUE FRANÇAISE DE MÉTROLOGIE, 34, Volume 2, (2014)

Reply to comment on: ‘Does an interfrometer test the gravitational redshift at the Compton frequency?’
P. Wolf, L. Blanchet, C.J. Bordé, S. Reynaud, C. Salomon, and C. Cohen-Tannoudji
Class. Quantum Grav. 29, 048002 (2012)

Space Clocks and Fundamental Tests: the ACES experiment
Luigi Cacciapuoti and Christophe Salomon
EPJ Special topics, 172, 57 (2009)

Overview

Proposed in 1997, the PHARAO/ACES experiment is a space mission in fundamental physics with two atomic clocks on the International Space Station, a network of ultra-stable clocks on the ground in national metrology institutes, and space-to- ground time transfer systems. The core of the flight instruments is a cold atom cesium clock designed to operate in micro-gravity conditions, the PHARAO clock. This clock has been designed by LKB, SYRTE, and CNES, and constructed by French companies under CNES funding. The other elements of the flight payload include a hydrogen maser developed by SpectraTime (CH), a high precision time transfer system in the microwave domain developed by TimeTech (DE) and Airbus (DE), and a laser time transfer developed by the University of Prague (CZ) and Technical University Munich (DE). The satellite payload is assembled by Airbus (DE) under ESA funding and ESA is responsible for launch and operations of the ACES mission. The ACES flight instruments are completed and launch in space is planned for early 2018 for a mission duration of three years.

The ACES scientific objectives have four main components, the operation of a laser-cooled cesium primary standard in space, a precision measurement of the Einstein effect, the gravitational shift of the clock frequency predicted by General Relativity, tests of Lorentz invariance, and a search for time or spatial variations of fundamental physical constants by long-distance ground clock comparisons.

According to the geometric nature of Einstein’s description of gravity, rates of clocks located at different gravitational potentials will differ by alpha Delta U/c^2 where c is the speed of light in vacuum and alpha =1 in Einstein general relativity. The ACES two-way microwave time transfer system between PHARAO and laboratories equipped with ground terminals will allow to retrieve the desynchronization between PHARAO and ground clocks with picosecond precision. Comparing the measured desynchronization to Einstein’s model will allow to constrain Einstein’s prediction at the level of 2.10^-6 .

ACES data analysis
A first step in preparing ACES data analysis has been to generate the program retrieving the desynchronization between PHARAO and ground clocks from raw Microwave Link data, using a dedicated time transfer model. This part of the work is done in the theory group of SYRTE which is a data analysis center for ACES. The second step, which is currently ongoing, is to develop the software for testing the gravitational redshift with data acquired during the mission. It will collect measured desynchronizations between PHARAO and cesium clocks in several laboratories on ground, as well as ISS orbitography data for the gravitational potential determination, and evaluate Einstein’s prediction. Adjusting the data to the model will constrain the coefficient alpha.
Beyond the Standard Model and General Relativity
Beyond testing General Relativity, fundamental tests can also be analyzed in alternative theoretical frameworks. We have dedicated recent work on a general framework, the Standard Model Extension (SME), for testing the fundamental principle of Special Relativity, i.e. Lorentz Invariance. In collaboration with Quentin Bailey from the Embry-Riddle Aeronautical University (USA), we have investigated prospects of cold atom interferometers for these tests. We also investigated alternative experiments, such as the Microscope satellite mission testing the Universality of Free Fall around the Earth, launched in May 2016. Tests with cold atom fountains such as PHARAO offer very promising perspectives. A previous test on Earth with spin-polarized states had led to an improvement by up to 13 orders of magnitude on some of the SME coefficients for Lorentz violation. We are currently investigating a more detailed model and analysis for this test which constrains a new SME coefficient, with an improvement by 5 orders of magnitude.

Useful Links

PHARAO
SYRTE