Berlin 2005 – scientific programme

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A: Atomphysik

A 8: Poster HU 1

A 8.18: Poster

Saturday, March 5, 2005, 08:30–18:30, Poster HU

Measuring ℏ/M_Cs using atom interferometry for a determination of the fine structure constant α — •Chris Vo, Sheng-wey Chiow, Quan Long, Holger Müller, and Steven Chu — Physics Department, Stanford University, Stanford, CA-94305

We present an atom interferometer to measure ℏ/M_Cs, where ℏ is Planck’s constant and M_Cs is the mass of a cesium atom, aiming for an accuracy exceeding 10⁻⁹. This will lead to a better determination of α. Comparing this result to measurements of α based on the anomalous magnetic moment of the electron will allow us to test the underlying quantum field theory with sensitivity to non-QED effects.

The experiment will measure the recoil frequency ω_r=ℏ k²/M_Cs∼2π· 4 kHz in a fountain of molasses and lattice cooled cesium atoms. We will use π/2 atom beam splitters based on multi-photon Bragg diffraction. To increase the number of recoils we plan to apply additional π-pulses. To cancel vibrational noise and other systematic effects a system for differential measurement between two interferometers with counterpropagating laser beams is being build. Therefore, each of the pulsed beams contains two frequencies. We achieve a noise of -138dBc/Hz for the differential phase within each beam. Common-mode phase noise is removed within each pulse using a high-speed feedback system. The correct beam alignment will be provided with microradian accuracy by a feedback system based on optical interferometry.