In atomic physics, a dark state refers to a state of an atom or molecule that can not absorb (or emit) photons. All atoms and molecules are described by quantum states; different states can have different energies and a system can make a transition from one energy level to another by emitting or absorbing one or more photons. However, not all transitions between arbitrary states are allowed. A state that cannot absorb an incident photon is called a dark state. This can occur in experiments using laser light to induce transitions between energy levels, when atoms can spontaneously decay into a state that is not coupled to any other level by the laser light, preventing the atom from absorbing or emitting light from that state. A dark state can also be the result of quantum interference in a three-level system, when an atom is in a coherent superposition of two states, both of which are coupled by lasers at the right frequency to a third state. With the system in a particular superposition of the two states, the system can be made dark to both lasers as the probability of absorbing a photon goes to 0.
Read more about Dark State: Three-level Systems
Famous quotes containing the words dark and/or state:
“Hast ever ben in Omaha
Where rolls the dark Missouri down,
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And all the houses are afloat?...
If not, take heed to what I say,
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—For the State of Nebraska, U.S. public relief program (1935-1943)
“I ask especially that no state shall, by law or otherwise, authorize the return of the saloon, either in its old form or in some modern guise.”
—Franklin D. Roosevelt (1882–1945)