The Quantum Zeno Effect

Abstract The quantum Zeno effect is one in which a quantum system never jumps to a new state if an experimenter keeps observing it. This effect is illustrated in several examples. The chapter describes the measurement of the state of a two-level atom under radiation that would normally cause the atom to change to the other state. Polarized photons can pass through optically active material multiple times, with polarization measurement at each stage, so that the polarization does not change. One can use superposition and interference to do interaction-free measurements. A hypothetical bomb-detection device (the EV effect) uses this method to tell that a bomb is not a dud without exploding it. An actual experimental used interference to detect the position of a mirror, which is never touched by any photon. Experimenters have also formed an image using photons that never touch the object imaged.