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Lecture: April 3, 2019
Macroscopic Quantum Phenomenon
• (1) Superconductivity
• (2) Quantization of Resistance
• (3) Bose Einstein Condensation
• Lasers
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Superconductivity
Nobel Prizes:
(1) Heike Kamerlingh Onnes (1913): Experimental Discovery of Superconductivity: About
4 degrees Kelvin (-452 degrees Fahrenheit, -268 degrees Celsius),
(2) John Bardeen, Leon N. Cooper, and J. Robert Schrieffer (1972), ”for their jointly
developed theory of superconductivity, usually called the BCS-theory”
(3) Georg Bednorz and K. Alex Mller (1987) - High Temperature Superconductivity: 30
degrees Kelvin.
( Latest : about 92 degrees K
Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion
of magnetic fields occurring in certain materials when cooled below a characteristic critical
temperature. It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911
in Leiden.
Two important properties of superconductors: (1) Zero Resistance, so they conduct without
heating the wires (2) Repel Magnetic Field
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Applications:
Two important applications are in MRI and particle accelerators. This is because
superconductors give us very powerful electromagnets.
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Superconducting magnet: An electromagnet made from coils of superconducting wire. They
must be cooled to very low temperatures during operation.
In its superconducting state the wire has no electrical resistance and therefore can conduct
much larger electric currents than ordinary wire, creating intense magnetic fields.
Superconducting magnets can produce greater magnetic fields than all but the strongest
non-superconducting electromagnets and can be cheaper to operate because no energy is dissipated
as heat in the windings.
The most widely used application for superconductors is an MRI machine commonly found in
hospitals. Only a superconductive system could allow the energy required to generate a magnetic
field that powers an MRI, which can be anywhere from 2,500 times to 10,000 times the strength
of Earths magnetic field, to be economical.
Another important application is in particle accelerators, like the kind used in CERNs Large
Hadron Collider (LHC) or its proposed Future Circular Collider.
If the MRI machine sounds powerful, the LHC is an absolute beast. Sending trillions of
particles around 27km of tunnels at speeds close to the speed of light, keeping the particle beam
stable and moving along the precise path requires a magnetic field of immense power, more than
100,000 times the Earths magnetic field. This requires an enormous amount of energy, the kind
that superconducting coils can provide.
The Future of Superconductivity
There is a lot we donot know about superconductive materials, and we are developing new
applications for superconductors every day.
The hope is to one day use superconductivity in power transmissions, which would
dramatically reduce energy costs around the world. Mag-lev trains, which use superconductivity
to hover a train car above the rail, thereby eliminating friction that might slow a train down, may
be the future of transportation.
Who knows? Maybe one day we will have electronics that utilize superconductors to give us
smartphones that only need to be charged once a month or more.
Its anyones guess, but with the rapid advances in our technology, well all likely see
superconductivity in our lives as a regular feature sooner rather than later.
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QUANTUM HALL EFFECT
Resistance R of some sheets of material, in a magnetic field assumes quantized values that
depend on charge of the electron and Planck constant.
Conductance = 1Resistance
= ne2
h, n = 1, 2, 3....
• Why is the resistance quantized
• Why is this quantization observed with extreme precision ( better than one part in billion )
• Why is the conductivity independent of geometry of the sample and impurities in the
sample ??
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Nobel Prizes:
(1) Von Klitzing in 1980, who was at the time a Heisenberg fellow at the University of
Wrzburg
(2) Robert Laughlin, 1990 ( For theoretical work on fractional quantum Hall effect )
(3) David Thouless for theoretical explanation of Quantum Hall Effect.
This mysterious phenomenon was explained by David Thouless described theoretically, using
TOPOLOGY and was awarded Nobel prize in 2016.
<https://www.nobelprize.org/prizes/physics/2016/
prize-announcement/>
Bose Einstein Condensate
Macroscopic Number of Bosons at very low temperature form a new kind of quantum state
that exists in lowest possible quantum state.
This state was first predicted, generally, in 1924-25 by Satyendra Nath Bose and Albert
Einstein.
On June 5, 1995 the first gaseous condensate was produced by Eric Cornell and Carl Wieman
at the University of Colorado at Boulder NIST-JILA lab, in a gas of rubidium atoms cooled to 170
nanokelvin.
Shortly thereafter, Wolfgang Ketterle at MIT demonstrated important BEC properties. For
their achievements Cornell, Wieman, and Ketterle received the 2001 Nobel Prize in Physics.
BEC is a new state of matter where particles loose their identity as de-Broglie wave length of
different particles overlap. Such a state of matter is a quantum mechanical state whose properties
can be tamed.
Nobel Prizes:
The Nobel Prize in Physics 2001 was awarded jointly to Eric A. Cornell, Wolfgang Ketterle
and Carl E. Wieman ”for the achievement of Bose-Einstein condensation.
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APPLICATIONS: They have applications in clock precision, new type of lasers and sensors
and also exploring new phenomena in physics.
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