Berlin 2014 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 9: Precision spectroscopy of atoms and ions II (with Q)
A 9.3: Vortrag
Montag, 17. März 2014, 14:30–14:45, BEBEL E42
Measurement of the forbidden 2 3S1 - 2 1P1 transition in quantum degenerate helium — •Remy Notermans and Wim Vassen — LaserLaB, Department of Physics and Astronomy, VU University Amsterdam, The Netherlands
There is a longstanding 6.8 (3.0) MHz discrepancy between QED theory and the experimental value of the ionization energy of the 2 1P1 state in helium. We present the first measurement of the forbidden 887-nm 2 3S1 - 2 1P1 transition in a quantum degenerate gas of 4He*, using the experimental setup as used to measure the doubly forbidden 2 3S1 - 2 1S0 transition by van Rooij et al. (Science 333, 196 (2011)). The low temperature of the gas (∼1 µK) allows us to observe the transition close to its natural linewidth of 284 MHz.
From our measurements we obtain the transition frequency with a preliminary accuracy of 0.57 MHz, i.e. at 0.2% of its natural linewidth. Our result already deviates >3σ from the current QED theory for the 2 1P1 ionization energy. Recent measurements by Luo et al. of the 2 1S0 - 2 1P1 and 2 1P1 - 3 1D2 transitions in a RF discharge cell (PRL 111, 013002 (2013) and PRA 88, 054501 (2013)) agree with our work, confirming the discrepancy with theory.