Elementary particles can be stored one or two at a time in a Penning trap. The trap can be though of as a miniature accelerator for a single isolated elementary particle. In some circumstances, the particle-plus-trap system is better regarded as a designer atom. The particle is bound to a "nucleus" that resides on the outside, and is the combination of magnetic and electric fields that are arranged and adjusted by the experimenter. Two recent illustrations will be used. The charge-to-mass ratios of an antiproton and proton have been recently compared at an accuracy of 9 parts in 10^11, nearly a million times higher accuracy than achieved earlier by exotic atom techniques. The relativistic "mass increase" is easy to see and is crucial to the measurement, even when the antiproton has only a few eV of energy. Clearly observed quantum jumps between the Fock states of a one-electron cyclotron oscillator provide the second illustration. For the first time the temperature of such a system is lowered below 4 K, all the way to 70 mK. As the temperature is lowered, the frequency of the observed absorptions and emissions, stimulated by blackbody photons, decreases dramatically.