Quantum Zeno Effect shows that a system cannot alter its state during observation. It is a feature of the quantum world, wherein frequent measurement of a particle can stop its time evolution. We can understand this with the help of daily life observations. For example,  it “feels” like it takes longer to complete a minute than usual when you are observing a clock. It also “feels” like it takes longer for boiling water to boil when you are observing it. This Is not literally true, it is just a way to explain what we will be discussing further.

Zeno Effect in Short

To explain the Zeno-effect we can take the example of an electron transition. When an electron jumps from higher to lower energy level, it emits light. This is spontaneous emission. But, when the movement of the electron is “observed” the Quantum Wave Function collapses and the electron returns to its excited/higher energy state. The frequent measurement of the electron slows down the decaying process. Its not easy to acquire the Zeno Effect. We have to measure the electron really fast- thousands of times every second.

Anti-Zeno Effect

Physicists put forth an interesting idea in 1977. The frequent measurement could also accelerate decaying processes. They call it the Anti-Zeno Effect. A system can acquire either Zeno effect or Anti-Zeno effect. It is much like Schrödinger’s Cat. Imagine an unstable quantum system. It is in a superposition of two states before measurement. Take “Up” and “Down” as an example for the two states . But, the moment we measure it, the wave function collapses and it acquires a definite state, either Up or Down. 

Zeno effect in experiments

An experiment was performed in 1989, where 5000 Beryllium cations were surrounded by an electric and magnetic field in a Penning trap and laser cooled to below 250 microkelvins (near absolute zero).  A resonant radio frequency magnetic field was applied, causing a jump from ground state to excited state. A bunch of ultraviolet pulses were fired and we observed ion traps. The results were in favor; there was a significant reduction in the transition.

In 2001, Mark Raizen successfully observed the quantum Zeno effect as well as the anti-Zeno effect. They used ultracold sodium atoms to perform quantum tunneling and observed suppression as well as acceleration.

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