Condensate of Bump-Einstein - SpeedyLook encyclopedia

Predictions of Bump and Einstein

The quantum statistics implied in the phenomenon of condensation of Bump-Einstein relate to the particles belonging to the family of the Boson S, which are the particles of whole Spin, in opposition to the family of the fermions which are of spin half-entirety.

Satyendra Nath Bose proposed statistics for the photons different from the traditional statistics of Boltzmann, while being based on the possibility for several Photon S of being in the same state and on the absolute indiscernibility of two of the same photons quantum state.

Albert Einstein generalized these statistics with all the bosonic particles, which they are nonmass, like the photon, or mass, like the helium 4 atoms.

The study by this last of monoatomic perfect gas bosonic showed the existence of a transition from phase between traditional gas and a state of the matter where the atoms accumulate in the quantum state of lower energy, when the temperature is decreased. This phase is today called a condensate of Bump-Einstein. The Manuscrit of Albert Einstein, titrated ideal Quantum theory off the monatomic gas , gone back to December 1924 was discovered in the files of the Lorenz institute of the University of Leyde. Illustrations

Superfluid helium

After the experimental discovery of the Superfluidity of the Helium 4 liquid at low temperature by Pyotr Kapitsa, John Allen and Gift Misener, Fritz London proposed the existence of a bond between this phenomenon and the condensation of Bump-Einstein. One has since overdraft that at very low temperature, approximately 10 % of the atoms occupy the same quantum state, forming a condensate indeed. However, from the strong interactions between helium atoms, the proportion of condensed atoms remains weak, even at very low temperature, whereas the whole of the fluid has the superfluid properties. This suggests an important difference between the phenomenon of superfluidity and the phenomenon of condensation of Bump-Einstein.

Diluted atomic gases ultrafroids

The physics of helium 4 at very low temperature is very complex because of the strong interactions between atoms. In order to be able to study and exploit more simply the phenomenon of condensation of Bump-Einstein, one sought to observe it for very diluted systems, closer to the perfect gas which had been the model initially presented by Einstein.

Obtaining a condensate

The experimental observation of the condensates was possible thanks to the development of the techniques of Refroidissement of atoms per laser. The very low temperatures reached made it possible to reach the mode of condensation for sufficiently diluted gases so that the interactions do not mask the phenomenon of condensation. In 1995, a team of laboratory NIST/JILA (Boulder, Colorado, the United States), directed by Eric Cornell and Carl Wieman, managed to obtain during a few seconds a condensate of Bump-Einstein; it consisted of a few thousands of atoms of Rubidium prérefroidis by laser, then cooled front by “evaporation” in a magnetic trap. The temperature of gas was then about 100 nK. The Nobel Prize of physique 2001 was decreed with these two researchers, accompanied by Wolfgang Ketterle.

Physical properties

; Perfect gas of Bump Einstein showed into 1925 that identical bosons, without interaction between them, with thermodynamic balance, condense in a new state of the matter at a sufficiently low temperature. This state is today called condensate of Bump-Einstein; it is characterized by a macroscopic population of the quantum state of lower energy. The temperature of change of state is given by

$T_c= \ left (\ frac {N} {\ zeta (3/2)}\ right) ^ {2/3} \ frac {h^2} {2 \ pi m k_B},$

where

Tc is the temperature of change of state,
N the density out of bosons,
m the mass of a boson,
H the Constante of Planck,
KB the Boltzmann constant and
ζ the Fonction zeta of Riemann: ζ (3/2) ≈ 2,6124.

London noticed that the temperature of the superfluid transition from helium 4 (2,2 K) is of the same order of magnitude as the temperature of condensation of Bump-Einstein of a perfect gas of the same density than liquid helium (3,2 K), from where its intuition that the two phenomena are dependant. Superfluid liquid helium is however very different from the model of perfect gas.

The gas condensates obtained recently are approximately a billion times more diluted than liquid helium (10 atomes/m against 10 27 atomes/m); the temperature of condensation is then about the microkelvin.

; Effect of the interactions If the weakness of the interactions explains the success of the model of perfect gas to predict certain properties of the gas condensates, other effects can be included/understood only by taking account of the interactions between atoms, for example the size of the trapped condensate, its superfluidity or its frequencies of oscillation when one makes it vibrate.

Besides the phenomenon of Résonance of Feshbach makes it possible to change the force of the interactions while plunging the condensate in a magnetic field. One can thus study situations where the atoms of the condensate are strongly correlated. These studies can be useful for the comprehension of complex phenomena of the physics of the condensed matter, like the Transition from Mott.

; Atomic interferences A condensate forms a coherent matter wave. Two packages of wave resulting from the same condensate or two different condensates interfere when they are superimposed, in a way similar to the figure of Interférence of the holes of Young in optics (I.Bloch and Al Nature 403 166 2000).

An atomic cloud ultrafroid trapped in a optical Network form a series of spaced condensates régulièrements which, when they interfere all together, can form figures of very pricked interferences, just like the figure of Diffraction of a light wave by a network.

; Condensate in rotation and vortex

The setting in rotation of a condensate reveals in a spectacular way the constraints that imposes quantum mechanics. It is impossible to make turn a condensate in block, with the image of a traditional object. The setting in rotation is accompanied by the creation of vortex, i.e. of lines the length of which the density is null and around of which the circulation speed is quantified. The first observation of vortex was carried out in the team of Jean Dalibard at the laboratory Kastler Brossel (Paris, France).

; Josephson effect

; Collective excitations

Applications

An application is the realization of Lasers to atoms, i.e. of instruments able to deliver a beam of atoms being all in the same state, following the example photons of a laser beam. That would render great services to atomic optics and interferometry, with chemistry (study of reactions between two atomic beams under conditions very well defined and controlled, condensates of molecules, etc). Several teams of physicists arrived, since 1997, to produce a laser effect with atoms, the principle being of forming a condensate initially then to extract by an adequate means part of the condensed atoms. But much of way remains to traverse before arriving at atomic flows of appreciable intensity and duration…

See too

External bonds

a conference of Claude Cohen-Tannoudji on the question
a conference of Sebastien Balibar about superfluidity
Conductivities and supraconductivity a conference with the UTLS of Jacques Lewiner
a conference of Jean Dalibard on the condensates of Bump-Einstein
Observation of a condensate of Bump-Einstein in BaCuSi₂O₆ (Mr. Jaime '' and Al '' PRL 93 087203 2004)
Observation of a condensate of Eintein Bump of let us polaritons in a microcavity, a conference of Benoit Deveaud

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