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:
“Later you hear it wander the dark house
Like a mother who rises at night to seek a childhood picture;
Or it goes to the backyard and stands like an old horse cold in the
pasture.”
—Robert Penn Warren (1905–1989)
“I am willing to pledge myself that if the time should ever come that the voluntary agencies of the country together with the local and state governments are unable to find resources with which to prevent hunger and suffering ... I will ask the aid of every resource of the Federal Government.... I have the faith in the American people that such a day will not come.”
—Herbert Hoover (1874–1964)