Interaction-free measurement
In physics, interaction-free measurement is a type of measurement in quantum mechanics that detects the position, presence, or state of an object without an interaction occurring between it and the measuring device. Examples include the Renninger negative-result experiment, the Elitzur–Vaidman bomb-testing problem, and certain double-cavity optical systems, such as Hardy's paradox.
In Quantum Computation such measurements are referred to as Counterfactual Quantum Computation, an idea introduced by physicists Graeme Mitchinson and Richard Jozsa. Examples include Keith Bowden's Counterfactual Mirror Array describing a digital computer that could be counterfactually interrogated to calculate whether a light beam would fail to pass through a maze.
More recently the idea of counterfactual quantum communication has been proposed and demonstrated.
Initially proposed as thought experiments, interaction-free measurements have been experimentally demonstrated in various configurations.
Interaction-free measurements have also been proposed as a way to reduce sample damage in electron microscopy.
