Aspect's experiment

Aspect's experiment was the first quantum mechanics experiment to demonstrate the violation of Bell's inequalities. Its 1982 result allowed for further validation of the quantum entanglement and locality principles. It also offered an experimental answer to Albert Einstein, Boris Podolsky, and Nathan Rosen's paradox which had been proposed about fifty years earlier. The experiment was led by French physicist Alain Aspect at the École supérieure d'optique in Orsay between 1980 and 1982. Its importance was immediately recognized by the scientific community. Although the methodology carried out by Aspect presents a potential flaw, the detection loophole, his result is considered decisive and led to numerous other experiments (the so-called Bell test experiments) which confirmed Aspect's original experiment. For his work on this topic, Aspect was awarded part of the 2022 Nobel Prize in Physics. The experiment must be placed in its historical and scientific context in order to be fully comprehended. Quantum entanglement Quantum entanglement is a phenomenon first theorized by Erwin Schrödinger in 1935. Quantum mechanics dictates that once two separate quantum systems (two particles for example) have interacted or if they have a common origin, they cannot be considered as two independent systems. The quantum mechanical formalism postulates that if a first system possesses a state, and the second a state, then the initial composite system can be represented by the tensor product of both states: . Once the interaction takes place and the two systems become entangled, the new composite state of the system, say , can no longer be written as a tensor product of two separate, individual states. It is a characteristic mark of entanglement that we have a global understanding of the properties of the composite system, and an intrinsic lack of knowledge about the two original separate states. The physical distance between the two systems plays no role in the entangled state (because no position variable is present).