The 2 3 P 1 -2 3 P 2 interval in helium is measured using microwave separated oscillatory fields. Our measured result is 2 291 177.53Ϯ 0.35 kHz . A disagreement with theory of over 15 kHz indicates a major problem with two-electron QED calculations. If this disagreement is resolved, measurements of both 2 3 P fine-structure intervals at this accuracy would lead to a six-parts-per-billion determination of the fine-structure constant.The present work continues the long history of precision measurements of the 2 3 P fine structure of helium ͓1-5͔. The main goal of these measurements is to determine the finestructure constant, ␣, from the larger ͑29.6 GHz͒ 2 3 P 1 -2 3 P 0 interval with the smaller ͑2.3 GHz͒ 2 3 P 1 -2 3 P 2 interval testing the two-electron QED theoretical calculations necessary to determine ␣. The present work differs by 36 standard deviations from theory ͓6,7͔. If this discrepancy is resolved, measurements of both 2 3 P finestructure intervals at the current accuracy would determine ␣ to 6 ppb. The most precise determination of ␣ ͑0.37 ppb͒ is from the magnetic moment of the electron ͑g e -2͒ ͓8͔. Independent determinations of ␣ ͓9͔ are needed to allow g e -2 to test QED to 0.37 ppb ͑the most precise test of QED theory͒ and to search for physics beyond the standard model ͓8͔.In this 2 3 P measurement separated oscillatory fields ͑SOFs͒ are used, compared to previous measurements which used continuous fields for excitation ͓1-5͔. SOFs allow for narrower linewidths ͑0.8-1.7 MHz͒ than the 3.25 MHz natural linewidth and also allow for a variety of line shapes. Figure 1 shows the experimental setup. A thermal beam of 2 3 S 1 metastable He is created in a dc discharge ͓3͔ and the 2 3 S 1 ͑m =0͒ state is depopulated by repeatedly driving 2 3 S 1 ͑m =0͒ -2 3 P 0 with a linearly polarized 1.08 m diode laser ͑A in Fig. 1͒. 2 3 S 1 ͑m = Ϯ 1͒ atoms are driven up to 2 3 P 1 ͑m =0͒ by a 15 ns laser pulse ͑B1 in Fig. 1, pulsed using two passes through an acousto-optic modulator͒, which is followed by the two 2.3 GHz SOF microwave pulses ͓P1 and P2 of Fig. 1͑c͒, of duration D = 50, 100, or 150 ns and separated in time by T = 300, 400, 500, or 600 ns͔ which drive the 2 3 P 1 ͑m =0͒ -2 3 P 2 ͑m =0͒ transition. Atoms can decay to 2 3 S 1 ͑m =0͒ only if the microwave transition is driven since the 2 3 P 1 ͑m =0͒ -2 3 S 1 ͑m =0͒ branching ratio is zero. This 2 3 S 1 ͑m =0͒ population is excited to 2 3 P 0 with laser C and the resulting fluorescence is collected on a 77 K InGaAs photodiode.The microwave transitions are driven inside of a 50 ⍀ coaxial transmission line ͓Fig. 1͑a͔͒. To double the signal size, another laser beam ͑B2͒ repeats the experiment on the other side of the 50 ⍀ line ͓inset of Fig. 1͑a͔͒. Microwaves ͑referenced to a Rb clock͒ are pulsed using fast switches and amplified to P = 25-125 W by a solid-state amplifier. The relative phase of P1 and P2 is controlled by additional switches which direct the pulses through paths L1 or L2 that differ in length by a half wavelength ͑ / 2͒. Every 79 ms, the rela...

Slow antihydrogen (H) is produced within a Penning trap that is located within a quadrupole Ioffe trap, the latter intended to ultimately confine extremely cold, ground-state H[over ] atoms. Observed H[over ] atoms in this configuration resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap. The number of detected H atoms actually increases when a 400 mK Ioffe trap is turned on.

For the first time a single trapped antiproton ( " p) is used to measure the " p magnetic moment " p . The moment " p ¼ " p S=ð@=2Þ is given in terms of its spin S and the nuclear magneton ( N ) by " p = N ¼ À2:792 845 AE 0:000 012. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment measured using the same method and trap electrodes gives " p = p ¼ À1:000 000 AE 0:000 005 to 5 ppm, for a proton moment p ¼ p S=ð@=2Þ, consistent with the prediction of the CPT theorem.

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