Atomic coherence
Encyclopedia
In physics
, atomic coherence is the induced coherence
between levels of a multi-level atom
ic system sometimes observed when it interacts with a coherent electromagnetic field
.
If a coherent, narrow bandwidth laser is applied to a two-level system, the wave function will undergo Rabi flopping (Rabi oscillation) between the ground and excited states. At some point in time the system will undergo spontaneous decay
and its wave function will collapse to the ground-state wave function. From there on, a new Rabi oscillation will start until the next spontaneous decay. Each spontaneous decay essentially changes the phase of the Rabi oscillation. If instead of single two-level system there is a large collection of identical two-level systems (like a lot of the same species atoms), then all of them will begin Rabi oscillation at the same time, and therefore all of them will be in phase with each other. But due to the spontaneous decay different atoms will collapse to their ground-state at different (and random) times and start a new Rabi oscillation. For this reason fewer and fewer atoms will be in-phase as time passes by. This is called decoherence
(meaning individual systems, e.g. atoms, are no longer coherent with each other).
Atomic coherence can involve more than two levels and its preparation more than a single laser.
An atomic coherence is essential in research on several effects, such as electromagnetically induced transparency
(EIT), lasing without inversion (LWI), enhanced dispersion without absorption, Stimulated Raman Adiabatic Passage (STIRAP) and nonlinear optical interaction with enhanced efficiency.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, atomic coherence is the induced coherence
Coherence (physics)
In physics, coherence is a property of waves that enables stationary interference. More generally, coherence describes all properties of the correlation between physical quantities of a wave....
between levels of a multi-level atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
ic system sometimes observed when it interacts with a coherent electromagnetic field
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
.
If a coherent, narrow bandwidth laser is applied to a two-level system, the wave function will undergo Rabi flopping (Rabi oscillation) between the ground and excited states. At some point in time the system will undergo spontaneous decay
Spontaneous emission
Spontaneous emission is the process by which a light source such as an atom, molecule, nanocrystal or nucleus in an excited state undergoes a transition to a state with a lower energy, e.g., the ground state and emits a photon...
and its wave function will collapse to the ground-state wave function. From there on, a new Rabi oscillation will start until the next spontaneous decay. Each spontaneous decay essentially changes the phase of the Rabi oscillation. If instead of single two-level system there is a large collection of identical two-level systems (like a lot of the same species atoms), then all of them will begin Rabi oscillation at the same time, and therefore all of them will be in phase with each other. But due to the spontaneous decay different atoms will collapse to their ground-state at different (and random) times and start a new Rabi oscillation. For this reason fewer and fewer atoms will be in-phase as time passes by. This is called decoherence
Quantum decoherence
In quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. A consequence of this dephasing leads to classical or probabilistically additive behavior...
(meaning individual systems, e.g. atoms, are no longer coherent with each other).
Atomic coherence can involve more than two levels and its preparation more than a single laser.
An atomic coherence is essential in research on several effects, such as electromagnetically induced transparency
Electromagnetically induced transparency
Electromagnetically induced transparency is a coherent optical nonlinearity which renders a medium transparent over a narrow spectral range within an absorption line...
(EIT), lasing without inversion (LWI), enhanced dispersion without absorption, Stimulated Raman Adiabatic Passage (STIRAP) and nonlinear optical interaction with enhanced efficiency.