Precision Microwave Measurement of the23P1−23

Abstract

The 2(3)P(1)-to- 2(3)P(0) interval in atomic helium is measured using a thermal beam of metastable helium atoms excited to the 2(3)P state using a 1.08-microm diode laser. The 2(3)P(1)-to- 2(3)P(0) transition is driven by 29.6-GHz microwaves in a rectangular waveguide cavity. Our result of 29,616,950.9+/-0.9 kHz is the most precise measurement of helium 2(3)P fine structure. When compared to precise theory for this interval, this measurement leads to a determination of the fine-structure constant of 1/137.0359864(31).

Cold and trapped metastable noble gases

“…Different high-precision spectroscopy approaches ranging from optically-pumped magnetic resonance microwave spectroscopy (Borbely et al, 2009;George et al, 2001) to heterodyne frequency differences of the 1083 nm transitions (Giusfredi et al, 2005;Smiciklas and Shiner, 2010;Zelevinsky et al, 2005) have produced sub-kHz accuracy 2 3 P fine structure measurements with a remarkable agreement among them. In particular the recently reported 9 ppb accurate value for the largest interval ∆ν 2 3 P0−2 = 31 908 131.25 (30) kHz, would lead to an uncertainty of 4.5 ppb in the inferred value of α if the theory were exact (Smiciklas and Shiner, 2010).…”

Giant Helium Dimers Produced by Photoassociation of Ultracold Metastable Atoms

“…When we include the atomic fine structure in the Hamiltonian [18], the coupling gives rise to three distinct asymptotes and to anti-crossings between attractive and repulsive curves, leading to purely long-range potential wells [25]. We construct the fine-structure coupling phenomenologically from 2 3 P splittings that have been measured accurately [19,20]. If there is no rotation, only the projection Ω of the total electronic angular momentum on the molecular axis remains a good quantum number.…”

Prospects for precision measurements of atomic helium using direct frequency comb spectroscopy

“…Overall, experiment and theory are in reasonable agreement, although for many energy levels the theoretical uncertainties are smaller than the experimental ones. In a few important cases significant discrepancies arise, most notably for the fine structure of the 2 3 P state [2,3,4,5,6,7,8,9]. Of special interest is the ionization energy (IE) of the ground 1 1 S 0 state of 4 He, which provides a sensitive test of QED corrections for a two-electron system.…”

“…In a few important cases significant discrepancies arise, most notably for the fine structure of the 2 3 P state [2,3,4,5,6,7,8,9]. Of special interest is the ionization energy (IE) of the ground 1 1 S 0 state of 4 He, which provides a sensitive test of QED corrections for a two-electron system. It is known experimentally to about 45 MHz, a fractional accuracy of 9 × 10 −9 , and the most recent theoretical calculation has surpassed this with an estimated uncertainty of 36 MHz [10].…”

“…All would use direct frequency comb spectroscopy (DFCS), together with an ultracold 4 He sample, to greatly improve the accuracy of selected UV and far-UV transitions. Because narrow natural linewidths are required for high-resolution spectroscopy, all of the experiments involve either the ground 1 1 S 0 state or one of the two metastable states, 2 1 S 0 and 2 3 S 1 , which have lifetimes of 1/51 s and 8000 s, respectively [16,17].…”