JCJC SIMI 4 - JCJC - SIMI 4 - Physique des milieux condensés et dilués

High precision atom interferometry and test of quantum electrodynamics. – INAQED

Submission summary

The goal of this project is to determine the fine structure constant alpha with an uncertainty below 10^{-10}. This measurement will be three times more accurate than the measurement of alpha that is obtained using the quantum electrodynamics theory (QED) with the measurement of the anomalous magnetic moment of the electron. It will also be seven times more accurate than measurements not involving directly QED. It will therefore strengthen the test of QED using the anomalous magnetic moment of the electron. This project involves the construction of an atom interferometer in order to precisely deduce the ratio h/m between the Planck constant and the mass of an atom from atom recoil measurement. This ratio is actually the limiting factor of the most precise determinations of alpha that are independent of QED.

The quantum electrodynamics has been introduced in the 1940s in order to explain electromagnetism in the framework of quantum mechanics and special relativity. It succeed in describing two phenomena not described by the previous theory due to Dirac. Those phenomena, the Lamb shift and the anomalous magnetic moment of the electron are still used to precisely test this theory. Indeed, it is important for theoretical physics to test QED with a higher accuracy in order to confirm the Standard Model and possibly see effects beyond this model. In order to realise such a test, the fine structure constant which is the free parameter of QED need to be measured independently.

The ratio between the kinetic energy of the electron and its mass energy in the ground state of the hydrogen atom is directly linked to the fine structure constant. However, it cannot be deduced directly from hydrogen spectroscopy as one need to compare an energy expressed in terms of frequency $h\nu$ with an energy expressed in terms of mass $mc^2$. The purpose of our interferometer is to precisely measure such a ratio h/m using rubidium atoms. This measurement will also have an impact in the atomic mass community. Indeed, the international committee in charge of the definition of the International System of units (SI) plan to redefine the unit of kilogram using the Planck constant. Our measurement will therefore provide the best link between the atomic mass units and the SI.

We want to build an interferometer of the "next generation". The source of atom will use state-of-the art techniques developed for Bose-Einstein condensates (fast evaporative cooling in an optical dipole trap). We will also develop and implement new interferometric schemes in order to enhance the sensitivity of the interferometer. Such schemes based on "large momentum beamsplitter" are under development in many groups around the world as they promise significant improvement in atomic interferometer. This new project that follows more that 10 years of research in atom interferometry at the Laboratoire Kastler Brossel is part of this worldwide effort in atom interferometry. Our experiment will therefore not only affect the determination of alpha but also other applications of atom interferometry, especially inertial sensors for navigation or geophysics.

Project coordination

Pierre CLADÉ (Laboratoire Kastler Brossel) – pierre.clade@spectro.jussieu.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


LKB Laboratoire Kastler Brossel

Help of the ANR 288,080 euros
Beginning and duration of the scientific project: December 2012 - 48 Months

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