bound electrostatically with a proton, and the antiproton have the same charge and can therefore be simultaneously trapped. This design allows for quick interchange of the proton and the antiproton and so an instantaneous-type Lorentz test can be performed. The cyclotron frequencies of the two trapped particles were about 90 MHz, and the apparatus was capable of resolving differences in these of about 1.0 Hz. The absence of Lorentz violating effects of this type placed a limit on combinations of -type SME coefficients that had not been accessed in other experiments. The results appeared in Physical Review Letters in 1999. The Penning-trap group at the University of Washington, headed by the Nobel Laureate Hans Dehmelt, conducted a search for sidereal variations in the anomaly frequency of a trapped electron. The results were extracted from an experiment that ran for several weeks, and the analysis required splitting the data into "bins" according to the orientation of the apparatus in the inertial reference frame of the Sun. At a resolution of 0.20 Hz, they were unable to discern any sidereal variations in the anomaly frequency, which runs around 185,000,000 Hz. Translating this into an upper bound on the relevant SME background field, places a bound of about 10−24 GeV on a -type electron coefficient. This work was published in Physical Review Letters in 1999. Another experimental result from the Dehmelt group involved a comparison of the instantaneous type. Using data from a single trapped electron and a single trapped positron, they again found no difference between the two anomaly frequencies at a resolution of about 0.2 Hz. This result placed a bound on a simpler combination of -type coefficients at a level of about 10−24 GeV. In addition to being a limit on Lorentz violation, this also limits the CPT violation. This result appeared in Physical Review Letters in 1999. Lorentz violation in antihydrogen The antihydrogen atom is the antimatter counterpart of the hydrogen atom. It has a negatively charged antiproton at the nucleus that attracts a positively charged positron orbiting around it. The spectral lines of hydrogen have frequencies determined by the energy differences between the quantum-mechanical orbital states of the electron. These lines have been studied in thousands of spectroscopic experiments and are understood in great detail. The quantum mechanics of the positron orbiting an antiproton in the antihydrogen atom is expected to be very similar to that of the