This last of a series of three measurements improves the comparison of antiproton ͑p͒ and proton ͑ p͒ by almost a factor of 10 6 over earlier exotic atom measurements, and is the most precise CPT test with baryons by a similar large factor. Measuring the cyclotron frequencies of a simultaneously trapped p and H 2 ion establishes that the ratio of q͞m forp and p is 20.999 999 999 91 6 0.000 000 000 09, more than 10 times the accuracy over our previous measurement. This 9 3 10 211 comparison makes the first use of simultaneously trapped particles for sub-ppb spectroscopy. [S0031-9007(99)08869-9]

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The measured ratio of charge-to-mass ratios for the antiproton and proton is 1.000 000 001 5 6 0.000 000 001 1. This 1 part in 10 9 comparison (1 ppb) is possible because a singlep or p is now directly observed while trapped in an open access Penning trap. The comparison is the most accurate mass spectrometry of particles with opposite charge, and is the most sensitive test of CPT invariance for a baryon system. It is 40 times more accurate than our earlier comparison with many trapped antiprotons and protons, and is more than 45 000 times more accurate than earlier comparisons made with other techniques.

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Crystalline InMnAs quantum dots with symmetric single spin domain particles have been formed on GaAs substrates using molecular beam epitaxy. The structural and magnetic properties of the quantum dots are characterized by a variety of techniques. Their magnetization curve as a function of temperature indicates that the ferromagnetic transition temperature is as high as 400 K (see Figure).