2. POINTS TO PONDER
Introduction
The process
Importance
Few Applications
Conclusion
3. A Thought Experiment
Let us imagine throwing a
ball on the wall.
Probability of ball
reflecting back from the
wall is unity.
BUT WHAT WILL
HAPPEN IF WE
SQUEEZE DOWN THE
SIZE OF THIS BALL TO
THE DIMENSION OF
ELECTRONS ??
4. A Thought Experiment
The reflection coefficient
now is not UNITY.
There will be a small but
finite probability of
transmission of our ball.
SO WHAT IS THIS
HAPPENING HERE?
“QUANTUM
TUNNELLING”
5. What is Quantum Tunnelling ?
Quantum tunnelling refers
to the quantum
mechanical phenomenon
where a particle tunnels
through a barrier that
it classically could not
surmount.
6. The Process
This process relies on
Heisenberg’s Uncertainty
principle. Because this
process of tunnelling relies
on probability.
The probability of an
object tunnelling through a
barrier decreases with the
object's increasing mass
and with the increasing gap
between the energy of the
object and the energy of the
barrier.
7. Importance
Tunnelling occurs with barriers of thickness around
1-3 nm and smaller.
Tunnelling plays an essential role in several physical,
chemical, and biological phenomena, such as radioactive
decay or the manifestation of large kinetic isotope effects
in chemicals of enzymatic reactions.
Quantum tunnelling is essential for nuclear fusion in stars.
The astrochemical syntheses of various molecules
in interstellar clouds can be explained such as the
synthesis of molecular hydrogen, water (ice)
and Formaldehyde.
8. Applications of Quantum Tunnelling
Quantum biology
Electron tunnelling is a key
factor in many biochemical
redox reactions
(photosynthesis, cellular
respiration) as well as
enzymatic catalysis
Proton tunnelling is a key
factor in spontaneous
mutation of DNA.
9. Cold Emission
Cold emission of electrons
is relevant to the emission
of electrons in
semiconductor where they
randomly jump from the
surface of metals to follow
the voltage bias.
used in flash memory ,
vacuum tubes, as well as
some electron microscopes.
10. Quantum Conductivity
When a free electron wave packet encounters a long array
of uniformly spaced barriers the reflected part of the wave
packet interferes uniformly with the transmitted one
between all barriers so that there are cases of 100%
transmission.
The theory predicts that if positively charged nuclei form
a perfectly rectangular array, electrons will tunnel through
the metal as free electrons, leading to an extremely
high conductance.
11. Scanning Tunnelling Microscope
It operates by taking
advantage of the
relationship between
quantum tunnelling with
distance.
By using piezoelectric
rods that change in size
when voltage is applied
over them the height of the
tip can be adjusted to keep
the tunnelling current
constant.
12. Can humans tunnel ?
In principle, macroscopic
objects like us also obey the
laws of quantum
mechanics.
So can we also tunnel ?
14. Explanation
We are highly complex organism made up of an
astronomically large number of particles.
Even though each particle behaves like a wave, when
combined together these `matter waves' will interfere,
resulting in a cancelling-out of the peaks and troughs.
This decoherence is what prevents large objects from
displaying observable wave-like behaviour, including
tunnelling.
