Quantum realm is a term of art in physics referring to scales where quantum mechanical effects become important when studied as an isolated system. Typically, this means distances of 100 nanometers (10−9 meters) or less or at very low temperature. More precisely, it is where the action or angular momentum is quantized.
While originating on the nanometer scale, such effects can operate on a macro level generating some paradoxes like in the Schrödinger's cat thought experiment. Two classical examples are electron tunneling and the double-slit experiment. Most fundamental processes in molecular electronics, organic electronics and organic semiconductors also originate in the quantum realm.
The quantum realm can also sometimes involve actions at long distances. A well-known example is David Bohm's (1951) version of the famous thought experiment that Einstein, Podolsky and Rosen proposed in 1935 (EPR paradox). Pairs of particles are emitted from a source in the so-called spin singlet state and rush in opposite directions. When the particles are widely separated from each other, they each encounter a measuring apparatus that can be set to measure their spin components along various directions. Although the measurement events are distant from each other, so that no slower-than-light or light signal can travel between them, the measurement outcomes are curiously correlated.
- Classical limit
- Quantum limit
- Microscopic scale
- Macroscopic scale
- Schrödinger's cat thought experiment
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