Bose-Einstein condensation
description
Transcript of Bose-Einstein condensation
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 1
When Atoms Become Waves
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 2
BosonsBosonsFermionFermionss
Satyendra Nath Bose
No two identical fermions can be in the same
quantum state at same time.
Possible to put a large group of atoms in a single quantum
state
Integral multiple spin
Half integral spin
Particles
Enrico Fermi
Obey
Pauli exclusion principle
Phenomenon
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 3
Albert Einstein - adapted the work to apply it to other Bosonic particles and atoms. At a finite T, almost all of ples in a Bosonic system would congregate in the GND state. Quantum wave fns of each particle start to overlap,
Atoms get locked into phase with each other,
And loose their individual identity.
"Bose-Einstein condensation"
Bose - statistics for photons (the particles which make up light).
BEC historical background
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 4
o Absolute temperature T of a sample is proportionalto the quantity <v²>
o T <v2> / kB
o T is a measure of the velocity fluctuations inthe sample.
Then, the absolute temperature must by definition belarger than zero, and in addition, that if T = 0, then allparticles in the sample must be at rest.
Absolute temperature
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 5
5000 K. surface of the sun300 to 400 K. boiling and freezing points of water70 K. the freezing point of N2, high Tc superconductivity3 K. superconductivity and superfluidity.
Now possible to cool atomic systems to one millionth of a degree Kelvin, and even lower.
At these extreme temperatures, the world is an utterly strange place where our everyday's common sense is useless, quantum physics rules with its counterintuitive laws, and atoms behave as waves.
Absolute temp graph
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 6
A French prince and waves of matter
de Broglie’s wavelength:
= h / p as p associated .
To understand why it is so useful to think of ultracold atoms aswaves, let us relate their de Broglie wavelength totemperatures.
T <v2>
As p = mv p v p2 v2.
T <p2> T <p>
As = h / p 1/p
The (thermal) de Broglie wavelength of a sample is inverselyproportional to the square root of its temperature,
Colder sample, larger the de Broglie wavelength !!!
T
1
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 7
R.T. very small, Ao.
Impossible to observe with visible
light.
To image an atom X- ray. Much
energy destroy atoms
This is why at RT, the wave nature
of atoms is normally irrelevant,
and it is most useful to think of
them as particles.
If T to few K of less, very
large, comparable to, the
wavelength of visible light.
Visible light can impinge on atoms
without destroying them.
de Broglie’s wavelength/ 3
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 8
Above "conventional" methods, Magnetic trap 20 nK 2000 Rb atoms, This is the lowest temperature ever achieved.
Laser cooling
1. Atom-Light I nteraction
Spontaneous emissionh = E2 - E1
Momentum conservation, theatom experiences a kick inmomentum by the amountm = h/ in the directionopposite to the direction ofphoton emission.
Intensity of the light beam .
Cooling Atoms
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 9
Atom at rest irradiate 2lasers[right & left]
Frequency (Green) is chosen No absorption of a photon
nothing happens.
Now Atom moving [v] Frequencyappears higher; The light seems"more blue" Doppler effect
Frequency shift to v. Absorption Velocity kick: Velocity of the atom
is reduced. Same argument Effects of spontaneous emission.
2. Doppler cooling
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 10
3. Below the Doppler limit
Few mK, the so-called Dopplerlimit.
Detailed understanding reqd. By clever choice of electronic
orbits and laser arrangements,possible to force the atoms tomove in much the same way asmarbles on a corrugated roof.
Trick 2 "roofs" atoms jump one other located nearmaxima of the surface
As a result, the atoms areforced to always move "uphill",very much like Sisyphus of theGreek legend. Lose most oftheir energy
Few K for alkali atoms suchas Sodium.
Sisyphus cooling
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 11
Quite familiar from everydaylife.cup of coffeeHigh-velocity particles easilyescape from a trap<v2> lower, hence T.Gradually trap depth, T keep .Atomic densityExceedingly low temperatures,T ~ nK
4. Evaporative cooling
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 12
How are the atoms trapped?
300 m/s 20 m/s
Oven350 oC
LASER VacuumChamber[MOT]
[
Atoms tended to flow out of the pit at its centre. There they lost
their magnetic orientation because the magnetic field was zero.
By rotating the magnetic field of the atom trap, the hole could be
shut, and in June 1995 the researchers achieved BEC of a few
thousand rubidium atoms with mass number 87.
Method to achieve BEC
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 13
Higher Velocity atoms
Medium Velocity atoms Lower Velocity atoms
LASER Magnetic field
How to cool atoms ?
Atoms are cooled by laser beams from all
directions
They are confined by the laser beam and magnetic field
After optical laser cooling, the light is turned OFF and the atom cloud is confined in the magnetic field.
Method to achieve BEC/ 2
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 14
LASER and Magnetic Field Arrangements
MOT imagined picture
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BEC result/ 1
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The three pictures, obtained by the group of W. Ketterle at MIT, show the velocity distribution in the atomic sample, Zero velocity is at the center of the pictures.
Right picture, which corresponds to the lowest temperature, the broad distribution has all but disappeared, all atoms finding themselves in the condensate.
Lower temperatures (middle picture) Curve shape : qualitative change. Two distinct contributions, a broad one quite similar to that of the preceding case, and superimposed to it a sharply peaked one, also centered at v = 0. This contribution : fraction of atoms that form a condensate at the bottom of the trap.
The left picture : relatively high temperature, above the transition from "normal" gas to condensate. Broad velocity distribution with smooth distribution decreasing from the maximum at v = 0.
BEC result/ 4
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 17
Ketterle’s first interference
pattern.
The interference pattern between two expanding condensates resembles
that formed by throwing two stones into still
water.
Experimental proof of de Brogile’s hypothesis:
Interference
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Atom lasers
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 19
Condensate Atoms studied to date
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A BEC first achieved at 10:54 a.m. June 5, 1995, in a laboratory at JILA, a joint institute of CU-Boulder and NIST. The apparatus that made it is now at the Smithsonian Institution.
Bose-Einstein condensate of about 2,000 rubidium atoms that lasted for 15 seconds to 20 seconds. New machines can now make condensates of much greater numbers of atoms that last for up to 3 minutes.
Made visible by a video camera, the condensate looks like the pit in a cherry except that it measures only about 20 microns in diameter or about one-fifth the thickness of a sheet of paper.
Some more about BEC…..
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 21
Too new and we know too little about it for me to give you an answer. There are also some engineering problems that will have to be solved before BEC can be used for very much.
Jin and DeMarco cooled atoms that are fermions, the other class of quantum particles found in nature. This was important to physicists because the basic building blocks of matter -- electrons, protons and neutrons -- are all fermions.
Made possible by nudging super-cold atoms into a beam, the breakthrough could lead to a new technique for making extremely small computer chips, according to NIST Nobel Laureate William Phillips, who led the team. Eventually, such a device might be able to construct nano-devices one atom at a time.
Today, scientists around the world are manipulating condensates made from a variety of gases to probe their scientific properties. The condensate can be used to form an atomic laser and could one day lead to a better atomic clock.
What is Bose-Einstein condensation good for ?
Applications:
Apr 22, 2023 presentation by Dr. K.Y. Rajpure 22
The Royal Swedish Academy
of Sciences has awarded the
Nobel Prize in Physics for Nobel Prize in Physics for
20012001 jointly to Eric A. CornellEric A. Cornell,
Wolfgang KetterleWolfgang Ketterle and
Carl E. WiemanCarl E. Wieman
“for the achievement of Bose-
Einstein condensation in
dilute gases of alkali atoms,
and for early fundamental
studies of the properties of
the condensates”.
Nobel prize 2001
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Prof. Pierre Meystre - AvH FellowProfessor of Optical Sciences and PhysicsThe University of Arizona
Dr. C.D. Lokhande - AvH Fellow
My dear participants