1. The Amazing World of Quantum Mechanics
'Ishan Vikas' programme – 14th June 2017.
9.00 – a.m. – A1-NKN Room, Kamand Campus.
Aniruddha Chakraborty
School of Basic Sciences
Indian Institute of Technology Mandi,
Kamand, Himachal Pradesh, India.

2. Acknowledgement
Prof. K. L. Sebastian, Indian Institute of Science. Bangalore, India.

3. The Amazing World : Strange & Beautiful
Very
frightening
Just
beautiful!
Mathematics ?
Physics ?
Ack: Prof. K. L. Sebastian

4. Outline 1.Waves or Particles ? 2. Random Walk: Quantum Mechanics.
3. Uncertainty Principle.
4. Do we understand Quantum Mechanics?

5. World Around Us Macro-World (Our world) Meso-World ? Micro-World Large
(Nano-world)
Micro-World
(World of atoms/Molecules )
Small

6. Micro-World: World of Atoms, Molecules & Beyond
Microscopic world is the world of electrons, photons, protons, neutrons, atoms & Molecules.

7. particles of different size.
Macro-world: World of Particles
In our world we have
particles of different size.

8. Micro-world: World of Wavicle* (= wave plus particle)
(electrons, photons, protons, neutrons, atoms & Molecules)
Oh LORD, please, is it a
PARTICLE or a WAVE ???
Is it wave-particle
duality ?
* R. P. Feynman

9. The Amazing Micro-World
(electrons, photons, protons, neutrons, atoms & Molecules)
It is a PARTICLE in one experiment and it a WAVE in another experiment*.
*There are some rare experiments
where it is both (particle & wave).

10. Micro-world everything has significant dual Nature
(electrons, photons, protons, neutrons, atoms & Molecules)
On Mondays, Wednesdays and Fridays, it is a PARTICLE!
On, Tuesdays,Thursdays &
Saturdays it is a WAVE!
On Sundays ?
It is both!
Ack: Prof. K. L. Sebastian

11. Micro-world: Wave-particle duality
(electrons, photons, protons, neutrons, atoms & Molecules)
Is it a PARTICLE, which sometimes behave as a WAVE ?
OR.
Is it a WAVE, which sometimes behave as a PARTICLE ?
Prof. T. A. Gonsalves,
Director, IIT Mandi.

12. Whom do you see in this picture?
Macro-world example of duality
Whom do you see in this picture?
A young girl?
Old woman?
Ack: Prof. K. L. Sebastian

13. It is interesting but actually very simple!
Understanding Wave-Particle Duality
It is interesting but actually very simple!

14. History Exhibits interference, hence waves! Light is a beam
of particles
Huygens
Newton
EM Theory,
hence waves
In photoelectric effect, light behaves like particles
Maxwell
Einstein
In my scattering expts,
light - beam of particles
Compton
Ack: Prof. K. L. Sebastian

15. Two Slit Experiment: With Particles (bullets) Three ‘Different’ Experiments

16. Why count number of bullets ?
Single Slit Experiment with Particles (bullets)
Experiment 1 (Only slit 1 is open ) 1 2
Why count number of bullets ?

17. Intensity is given by number of bullets.
Single slit Experiment with particles (bullets)
Analysis of Data: I1 1
Intensity is given by number of bullets. 2

18. Single slit Experiment with particles (bullets)
Experiment 2 (Only slit 2 is open ) 1 I2
Why do the same
experiment again ? 2

19. Two slit Experiment with particles (bullets)
Experiment 3 (both slits are open )
I12
Some will go through
slit1 & others will go
through slit2. 1 2

20. Two Slit experiment: With Particles (bullets)
Three ‘Different’ Experiments
I12 I1 1
Behavior of bullets is simple ! 2 I2

21. Two Slit Experiment with waves (water)!
A bucket full of water !

22. Two Slit Experiment with waves (water)!
Do Waves Interfere !

23. Waves interfere really!
Water waves interference in real time
Waves interfere really!
Ack: Prof. K. L. Sebastian

24. Two Slit Experiment with Waves
Three ‘Different’ Experiments I1
I12 1 I2 2

25. Two Slit Experiments With electrons
Three ‘Different’ Experiments
I12 I1
Electrons are like water! 1 I2 2
INTERFERENCE!

26. Single electron Interference!
Two Slit Experiments with Single electron I1
I12 1 I2 2
Single electron Interference!

27. Does it go through both the slits?
Single electron Interference ! 1 2
Does it go through both the slits?
Ack: Prof. K. L. Sebastian

28. Analogy with Macro-world example ?
I can also try !
Ack: Prof. K. L. Sebastian

29. Any real Two slit experiment ?

30. So electron is like bullet !
What fraction of electron goes through which slit !
(Two slit experiment with observer)
I12 I1 1 I2
So electron is like bullet ! 2

31. Result depends on whether you observe or not!
With observer:
(Particle-like)
Without observer:
(Wave-like)

32. N-slit set-up 1 1 2 2 3 4 3

33. Complex N-slit set-up Even more Complex setup 1 Six slits set up 2
Ack: Prof. K. L. Sebastian

34. How does an electron move?
In the limit of infinite walls each with infinite slits…….
He is crazy!
Through all possible paths!
Ack: Prof. K. L. Sebastian

35. Haddock in the Evening We can only talk of Probabilities! BAR
Ack: Prof. K. L. Sebastian

36. Infinite Number of Different Paths
Some paths are more
probable than others
BAR
Uncertainty!!!
Ack: Prof. K. L. Sebastian

37. For wave there has to be an wave equation
E. SchrÖdinger
Ack: Prof. K. L. Sebastian

38. Who Understand Quantum Mechanics ?
"If you think you understand quantum mechanics,
you don't understand quantum mechanics.“
~ Richard Feynman
“The reason universities have students is so they
can teach the professors & Feynman was one of the best (students)“.
~ John Wheeler

39. REFERENCES 1. G. Gamow, Tompkins in Paperback, Canto Books. CUP, 1993.
R. Gilmore, Alice in Quantum Land, Affiliated East West Press Ltd
J. Gribbin, Schrodinger’s Cat, Black Swan, London, 1984.
J. Gribbin, Schrodinger’s Kittens, Little, Brown & Co. London, 1995.
G. Gamow and R. Stannard, The New World of Tompkins, Cambridge Univ. Press, 1999.
R. P. Feynamn, QED, Princeton University Press, 1988.
R.P. Feynman and A.R. Hibbs, Quantum Mechanics and Path Integrals, McGraw Hill, New York, 1965.

40. What do you think of Quantum Mechanics?OR
Ack: Prof. K. L. Sebastian