What is the name of the quantum phenomenon in which repeated measurements inhibit a system’s evolution?

The quantum Zeno effect is the inhibition of a quantum system’s evolution by repeated measurements.

A quantum state normally changes according to its time-evolution law. If measurements are made sufficiently frequently to ask whether the system remains in its initial state, the probability of finding it there can remain high. In the idealized limit of infinitely frequent measurements, evolution can appear frozen.

The effect is named after Zeno of Elea, whose ancient paradoxes concerned motion and repeated subdivision. The quantum version was discussed by Alan Turing in 1954 and formally described by Sudarshan and Baidya in 1977. Experiments have observed related behavior in atomic and optical systems.

The phrase does not mean that every observation literally stops all change. Real experiments involve finite measurement intervals, imperfect detectors, and possible transitions between different dynamical regimes. A related anti-Zeno effect can instead accelerate decay when measurements are timed appropriately.