Superposition,+Nonlocality+and+Entanglement


 * Superposition, Nonlocality and Entanglement **

**Superposition** The idea of superposition is not unique to quantum mechanics but is a general property of all waves. The process of adding different waves together is known as superposition. The interference pattern we saw in the two-slit experiment with light is a direct consequence of superposition of light waves. Just as it is possible to have a superposition of water waves or light waves, it is also possible to have a superposition of wavefunctions. Let’s look at a wavefunction that describes an electron with a particular energy. It is slowed down so that half its original energy remains. Its wavefunction will be altered. However, because of the possibility of superposition of these two different wavefunctions which describe the same electron with different energies, it is possible for the electron to exist in a state that is described by the third wavefunction. This new wavefunction is the sum of the first two wavefunctions. This means that a single electron in such a state is both moving fast and slow at the same time. (Not an average velocity) An electron might be in a state described by a wavefunction that is the sum of two or more wavefunctions which describe the position of the electron. The combined wavefunction will tell us that the electron is in more than one place at once. This sort of explains the double-slit experiment; the atoms being used would spread out into a cloud which drifts through both slits at once. In any case, we never see this strange state when we look at electrons. They only exist in one position. For example, if an electron is in superposition of being in two places at once, this means that if we repeatedly check an atom for its position, it would be in one of the places half of the time and in the other the rest of the time. In the double-slit experiment, by the time the combined wave-function reaches the back screen, there are places where the probability of an atom being there is high and places where they are low. However atoms only exist in one place at once, thus many atoms each with a similar probability distribution will form the pattern observed in the experiment. **Nonlocality** A quantum particle can experience something which is the effect of another quantum particle immediately, which means that something faster than light must have happened (a nonlocal connection) between them since time for the cause to travel to the affected particle is non-existent. Two particles can thus have a connection between each other no matter how far apart they are. **Entanglement** Entangled quantum particles experience nonlocality. In essence, two quantum particles which interact with each other can become correlated in the sense that their fates will be intertwined forever, however far apart they get until one of them interacts with a measuring device.