Mr. Pondet Ananchai, Thailand
pd.ananchai@gmail.com
Definition of Antibunching Phenomena
1. Bunching & Antibunching
The figure above illustrates the meaning of the terms bunching and
antibunching. Suppose the spheres in each row represent the positions of a
group of particles along a line. (They could also represent the arrival times at a
detector.)
• The middle row of spheres (blue) corresponds to normal, everyday,
independent particles. The spheres were placed at random positions on
a line and the position of each sphere is independent of all the others.
Sometimes they are close together sometimes they are far apart.
• The upper row (red) corresponds to particles exhibiting bunching. Note
that compared to the independent particles, the particles tend to clump
together. They are more often found together than independent
particles.
• The lower row (green) represents antibunched particles. In this case they
are more evenly spaced than independent particles. Indeed, they are
never found close together.
Bunching or antibunching can have any of several physical origins. An
obvious cause is interactions between the particles: if the particles attract each
other they will clump together (bunching), if they repel each other they will
spread out (antibunching) It is important to realize however, that in the
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Mr. Pondet Ananchai, Thailand
pd.ananchai@gmail.com
experiments we have done on helium atoms, such interactions are completely
negligible and that the origin of (anti-) bunching is a rather more mysterious
interference effect. The comparison of 3He and 4He confirms this. These two
isotopes are, apart from their mass and their spin, as similar as particles can
be. Yet, in the same apparatus under the same conditions, 3He shows
antibunching and 4He bunching, This difference is due only to the quantum
statistics, as determined by the spin (3/2 for 3He making it a fermion and 1 for
4He making it a boson).
2. Photon antibunching
It is made clear that this phenomenon reflects the corpuscular nature of
light and, hence, cannot be interpreted in terms of classical electrodynamics,
needing, instead, the quantum-mechanical formalism for its description. It is
shown in some detail that nonlinear interaction mechanisms like multiphoton
absorption and parametric three-wave interaction are suited to change the
photon statistical properties of incident (in most cases coherent) light such
that the output field will be endowed with antibunching properties. Special
emphasis is given to the problem of correctly specifying the dimensions of the
mode volume occurring in the usual single-mode treatment of the field, which
is, in fact, of great practical interest, since the magnitude of the antibunching
effect is determined by the inverse average number of photons contained in
that volume. In a later section it is pointed out that destructive interference
with a coherent reference beam provides a means of (a) effectively enhancing
photon antibunching that is already present in a high-intensity field, through
reduction of the intensity, and (b) transforming phase fluctuations produced in
a Kerr medium into antibunching-type intensity fluctuations. On the other
hand, there exists a way of directly generating light with antibunching
properties, the physical mechanism being resonance fluorescence from a
single atom.
3. References
“What is bunching and anti-bunching?” (online) available at
http://129.175.199.88/~helium/pictures/bunch-antib-en.pdf
(1 Dec 2011)
H. Paul (1982) Photon antibunching, Rev. Mod. Phys. 54, 1061–1102.
doi: 10.1103/RevModPhys.54.1061
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