Berlin 2005 – wissenschaftliches Programm
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A: Atomphysik
A 12: Precision Spectroscopy of Atoms and Molecules III
A 12.2: Hauptvortrag
Dienstag, 8. März 2005, 10:45–11:15, HU 3075
A new photon recoil measurement to determine the fine-structure constant α — •Holger Müller, Sheng-wey Chiow, Quan Long, Chris Vo, and Steven Chu — Physics Department, Stanford University, Stanford, CA94305
We aim for measuring the recoil frequency ωr=ℏ k2/MCs∼ 2π · 4kHz of a Cs atom that emits/absorbs photon momenta ℏ k for a new determination of α with an accuracy better than 10−9. This allows us to test the quantum field theoretical calculation of the electron’s anomalous magnetic moment, arguably the most accurate prediction in science, with sensitivity to the muon and non-QED terms.
We use a differential measurement between two atom interferometers having up to 100 positive and negative recoils, respectively. We use multiphoton Bragg diffractions between different momentum states, leaving the atomic states unaffected. We thus remove systematics such as sensitivity to magnetic fields and the ac Stark effect. The two interferometers are adressed simultaneously to cancel vibrational noise by two counterpropagating Raman laser pulses that consist of two frequencies each. Our setup generates these pulses with an ultra-low phase noise of -138dBc/Hz. We further stabilize the phase of the pulses as seen by the atoms, using a high-speed feedback that locks the phase of each pulse anew. We also present a feedback system that reduces misalignment of the counterpropagating beams to microradian accuracy, based on optical interferometry.