In 2001, Mark G. Raizen and his group at the University of Texas at Austin observed the quantum Zeno effect for an unstable quantum system, as originally proposed by Sudarshan and Misra. They also observed an anti-Zeno effect. Ultracold sodium atoms were trapped in an accelerating optical lattice, and the loss due to tunneling was measured. The evolution was interrupted by reducing the acceleration, thereby stopping quantum tunneling. The group observed suppression or enhancement of the decay rate, depending on the regime of measurement.