Download Bose Einstein Condensation

When Atoms Become Waves
5-May-17
presentation by Dr. K.Y. Rajpure
1
Phenomenon
Particles
Half integral
spin
Integral
multiple spin
Fermions
Bosons
Enrico Fermi
Satyendra Nath Bose
Obey
Pauli exclusion principle
No two identical fermions
can be in the same quantum
state at same time.
5-May-17
Possible to put a large group of
atoms in a single quantum state
presentation by Dr. K.Y. Rajpure
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BEC historical background
Bose - statistics for photons (the particles which make up light).
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"
5-May-17
presentation by Dr. K.Y. Rajpure
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Absolute temperature
o Absolute temperature T of a sample is proportional
to the quantity <v²>
o  T  <v2> / kB
o T is a measure of the velocity fluctuations in
the sample.
Then, the absolute temperature must by definition be
larger than zero, and in addition, that if T = 0, then all
particles in the sample must be at rest.
5-May-17
presentation by Dr. K.Y. Rajpure
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Absolute temp graph
5000 K. surface of the sun
300 to 400 K. boiling and
freezing points of water
70 K. the freezing point of N2,
high Tc superconductivity
3 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.
5-May-17
presentation by Dr. K.Y. Rajpure
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de Broglie’s wavelength:
A French prince and waves of matter
=h/p
as p  associated  .
To understand why it is so useful to think of ultracold atoms as
waves, let us relate their de Broglie wavelength  to
temperatures.
T  <v2>
As p = mv
pv 
p2  v2.
 T  <p2>

T  <p>
As  = h / p

  1/p

1
T
The (thermal) de Broglie wavelength of a sample is inversely
proportional to the square root of its temperature,
Colder sample, larger the de Broglie wavelength !!!
5-May-17
presentation by Dr. K.Y. Rajpure
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de Broglie’s wavelength/ 3
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, 
large,
comparable
to,
very
the
wavelength of visible light.
Visible light can impinge on atoms
without destroying them.
5-May-17
presentation by Dr. K.Y. Rajpure
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Cooling Atoms
Above "conventional" methods, Magnetic trap 20 nK 2000 Rb atoms,
This is the lowest temperature ever achieved.
Laser cooling
1. Atom-Light Interaction
Spontaneous emission
h = E2 - E1
Momentum conservation, the
atom experiences a kick in
momentum by the amount
m = h/ in the direction
opposite to the direction of
photon emission.
Intensity of the light beam .
5-May-17
presentation by Dr. K.Y. Rajpure
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2. Doppler cooling
 Atom at rest  irradiate 2
lasers[right & left]
 Frequency  (Green) is chosen
 No absorption of a photon 
nothing happens.
 Now Atom moving [v] Frequency
appears 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.
5-May-17
presentation by Dr. K.Y. Rajpure
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Sisyphus cooling
3. Below the Doppler limit
 Few mK, the so-called Doppler
limit.
 Detailed understanding reqd.
 By clever choice of electronic
orbits and laser arrangements,
possible to force the atoms to
move in much the same way as
marbles on a corrugated roof.
 Trick 2 "roofs" atoms jump one
 other  located near
maxima of the surface
 As a result, the atoms are
forced to always move "uphill",
very much like Sisyphus of the
Greek legend. Lose most of
their energy
 Few K for alkali atoms such
as Sodium.
5-May-17
presentation by Dr. K.Y. Rajpure
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4. Evaporative cooling
Quite familiar from everyday
life.
cup of coffee
High-velocity particles easily
escape from a trap
<v2> lower, hence T.
Gradually  trap depth, T keep
.
Atomic density
Exceedingly low temperatures,
T ~ nK
5-May-17
presentation by Dr. K.Y. Rajpure
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Method to achieve BEC
How are the atoms trapped?
300 m/s
Oven
350 oC
   
20 m/s
LASER
   
Vacuum
Chamber
[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.
5-May-17
presentation by Dr. K.Y. Rajpure
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How to cool atoms ?
Higher Velocity atoms 
Medium Velocity atoms 
Lower Velocity atoms 
LASER

Magnetic field

Method to achieve BEC/ 2
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.
5-May-17
presentation by Dr. K.Y. Rajpure
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LASER and Magnetic Field Arrangements
MOT imagined picture
5-May-17
presentation by Dr. K.Y. Rajpure
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BEC result/ 1
5-May-17
presentation by Dr. K.Y. Rajpure
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BEC result/ 4
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.
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.
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.
Right picture, which corresponds to the lowest temperature, the broad
distribution has all but disappeared, all atoms finding themselves in the
condensate.
5-May-17
presentation by Dr. K.Y. Rajpure
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Experimental proof of de Brogile’s hypothesis:
Ketterle’s first
interference pattern.
The interference pattern
between two expanding
condensates resembles that
formed by throwing two
stones into still water.
Interference
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presentation by Dr. K.Y. Rajpure
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Atom lasers
5-May-17
presentation by Dr. K.Y. Rajpure
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Condensate Atoms studied to date
5-May-17
presentation by Dr. K.Y. Rajpure
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Some more about BEC…..
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.
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.
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.
5-May-17
presentation by Dr. K.Y. Rajpure
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Applications:
What is Bose-Einstein condensation good for ?
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.
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.
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.
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.
5-May-17
presentation by Dr. K.Y. Rajpure
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The Royal Swedish Academy of
Sciences has awarded the Nobel
Prize in Physics for 2001 jointly to
Eric A. Cornell,
Wolfgang Ketterle and
Carl 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
5-May-17
presentation by Dr. K.Y. Rajpure
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Prof. Pierre Meystre - AvH Fellow
Professor of Optical Sciences and Physics
The University of Arizona
Dr. C.D. Lokhande - AvH Fellow
My dear participants
5-May-17
presentation by Dr. K.Y. Rajpure
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