Brief Histories: The Quantum Zeno Effect

The ‘Brief Histories’ series is a recurring profile of a fascinating theory or concept in science. For notifications of new articles and updates to the series, follow MFP on Twitter: @ThePhysicsBlog Modern physics is infamous for strange time-paradoxes. But the quantum Zeno effect is one in-particular that doesn’t involve relativity. The Inception Also known as the Turing paradox, the quantum Zeno effect occurs when a quantum system is measured frequently. ‘Zeno’ is a reference to the ancient Greek philosopher of the same name who posited that an object in flight cannot actually be moving if it cannot be observed in motion during a single instant. (Ancient Greek philosophers were often vexed by the infinitesimal calculus later resolved by Isaac Newton.) This paradox, known as Zeno’s arrow, is only loosely related to its quantum-namesake however. In quantum-mechanics, whenever a system is measured it’s wavefunction collapses. In essence, this implies that if a particle is measured frequently enough its probability of being in a particular location (it’s time-evolution), is suspended. The Argument Why does the observation of a particle force it to remain stationary? The simple answer is that every observation is actually an interaction in terms of a quantum system. Its impossible to register the position of a particle without that particle striking a detector, or more precisely, interacting with another system. Until such an event occurs, the particle cannot be thought of as a particle, only a probability wavefunction of a particle. The information about the particle’s location immediately after the interaction will again be described by a wavefunction. In the mid-20th century it was realized that the exponential decay rate of an unstable quantum system is protracted when the wavefunction is frequently collapsed. The Status Much experimental proof of the quantum Zeno effect has been documented dating back 30 years. Additionally the effect has also proven to be present in the natural magnetic compass mechanism of birds. Today the effect’s main application is in commercial atomic magnetometers. Researchers in the 1980s demonstrated the quantum Zeno effect extends beyond the formalism of the Copenhagen interpretation of quantum-mechanics, and is persistent in the many-worlds interpretation. However there still exist open questions regarding the effect in theoretical physics. Proceed to the Next Post: Brief Histories: The Big Bang

Have suggestions about future content or need help solving a physics/math problem? Tweet @ThePhysicsBlog