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:
“Between the dark and the daylight,
When the night is beginning to lower,
Comes a pause in the day’s occupations,
That is known as the Children’s Hour.”
—Henry Wadsworth Longfellow (1809–1882)
“The principal saloon was the Howlin’ Wilderness, an immense log cabin with a log fire always burning in the huge fireplace, where so many fights broke out that the common saying was, “We will have a man for breakfast tomorrow.””
—For the State of California, U.S. public relief program (1935-1943)