The slide discusses some basic information that I presented in my public talk titled "The future is quantum", at the Indian Institute of Science, Bengaluru, India. In this slide, I have covered the basics of quantum computing and quantum communication. Please write your suggestions to quantumaravinth@gmail.com. Looking forward to interacting with you

1. “THE FUTURE IS QUANTUM”
Aravinth Balaji Ravichandran
Research Assistant
Electrical Communication Engineering
Indian Institute of Science

3. WHEN?
HOW?
WHY?
WHAT?

4. WHAT IS A
QUANTUM
COMPUTER ?
• A Quantum computer is a
computing device which
harnesses quantum
mechanical laws to
process information.

5. CLASSICAL COMPUTERS
• Modern computers uses the laws of classical physics
(Newtonian) and mathematical logic (Boolean) to
perform computation.
• How can the computer decide?

6. WHY DO WE NEED A
QUANTUM COMPUTER?
• “Moore’s Law Is Dead. Now What?”, MIT
Technology Review, May 13, 2016
• “The chips are down for Moore’s law” Nature
530, February 11, 2016

10. MOORE’S LAW
• Things become complex when the spacing
between the components becomes smaller and
smaller.
• When the spacing between the components
reaches atomic dimensions, uncertainty principle
comes into picture.
• Heat effects of the components.
• Heat can be removed only from the surface

11. SERIAL AND PARALLEL
COMPUTATION
• Software for the classical computers are designed
for serial computation.
• Algorithms are written in a way the logic flows from
one point to another in time.

12. PARALLEL CLASSICAL COMPUTERS
• A problem is broken into parts having independent logic
and then they can be computed at the same time
• Example: Matrix Multiplication

13. PARALLEL CLASSICAL COMPUTERS
• Each one still does a serial computing
• Split up logic into n processors and execute at the
same time.
• n processors which would take up the job at the
same time and integrate them back.

14. INHERENT PARALLELISM
• Quantum Superposition.
• Can compute value of function of each input at the
same time.
• In other words, the parallelism is inherent.

15. LOSS OF ENERGY
• Every n bit of information increases the
thermodynamic entropy by !"#$!(&)
• This means there are lot of energy losses and the
computation becomes inefficient.
• This is called Landauer’s principle

16. REVERSIBLE COMPUTATION
• Computational gates (AND, OR, NAND, NOR) are
irreversible.
• Inputs cannot be traced back from the output.
• Information loss.
• Limit to which we perform work.

17. REVERSIBLE COMPUTATION
• Charles Bennett in 1973 found out that any
computation can be performed using only reversible
steps, and so in principle requires no dissipation and
no power expenditure.
• A reversible computer can run forward to the end of
a computation, print out a copy of the answer (a
logically reversible operation) and then reverse all of
its steps to return to its initial configuration.

18. HISTORY
“… trying to find a computer simulation of
physics, seem to me to be an excellent program
to follow out… and I'm not happy with all the
analyses that go with just the classical theory,
because nature isn't classical, dammit, and if
you want to make a simulation of nature, you'd
better make it quantum mechanical, and by
golly it's a wonderful problem, because it doesn't
look so easy.”
- RICHARD FEYNMAN (1981)

19. HISTORY OF QUANTUM
MECHANICS
• Physicists had a misapprehension that there is
nothing new to be discovered in Physics.
• Lord Kelvin’s statement.
There is nothing new to be discovered in physics now.
All that remains is more and more precise
measurements.

20. HISTORY OF QUANTUM
MECHANICS
• Challenged by Backbody spectrum.
• Reylegh, Jeans and Wien attempted solving the
blackbody problem.
• Max Planck solved it
• Considered energy as discrete entity as opposed to
continuous one.
• First quantization

21. HISTORY OF QUANTUM
MECHANICS
• deBroglie proposed dual nature of matter.
• Davison and Germer proved it experimentally.
• Schrödinger gave the wave equation for matter
waves which is called Schrödinger equation.

22. POSTULATES OF QUANTUM
MECHANICS
• With every physical system, there is associated an
abstract Hilbert space. Vectors in this space represent
the states of the system.
• Every physically observable quantity is represented by a
Hermitian operator.
• The experimentally measured values of the observable
can only be the eigenvalues of the operator
corresponding to that observable.
• The time evolution of a quantum system is Unitary
evolution and is given by Schrodinger equation.

23. QUBIT –
THE QUANTUM BIT
• The quantum “version” of classical
bit
• 0 becomes | ⟩
0 & 1 becomes | ⟩
1
• Quantum Superposition
| ⟩
Ψ = '| ⟩
0 + (| ⟩
1
• Probability of getting 0 ' )
• Probability of getting 1 is ( )
' ) + ( ) = 1
• Mathematically,
⟩
|Ψ = *+, cos
0
2
| ⟩
0 + *+3 sin
0
2
| ⟩
1
Bloch Sphere
Image Courtesy: IBM

24. MULTIPLE QUBITS
⟩
01 |01
⟩
10 |10
⟩
00 |00
⟩
11 |11
⟩
|Ψ = '((| ⟩
00 + '(*| ⟩
01 + '*(| ⟩
10 + '**| ⟩
11
* No pictorial representation for Multiple qubits

25. QUANTUM
GATES
• Single Qubit Gates
0 1 0 1 0
X ; Y ; Z
1 0 0 0 1
i
i
-
é ù é ù é ù
= = =
ê ú ê ú ê ú
-
ë û ë û ë û
+ - é ù
= = = ê ú
-
ë û
1
0 1 0 1 1 1
0 ; 1 ;
1 1
2
2 2
H H H
Pauli Gates
Hadamard Gate

26. MULTIPLE
QUBIT GATES
• C NOT gate
• CC NOT gate (Toffoli gate)
c
t c
t Å
c
ú
ú
ú
û
ù
ê
ê
ê
ë
é
0
1
0
0
1
0
0
0
0
0
1
0
0
0
0
1
U
t 2
1 c
c
t ×
Å
2
c 2
c

27. QUANTUM ANALOGUES OF
CLASSICAL GATES
x
1
y
1Å ×
x y
x
y
x
0 x
x
Classical circuit
x ( )
f x
f
x
0
m
Ä
x
g
f
U
Quantum circuit
The quantum NAND The quantum fanout

28. DIVINCENZO CRITERIA
A scalable
physical system
with well
characterized qub
its.
01
The ability to
initialize the
state of the
qubits to a
simple fiducial
state.
02
Long relevant
decoherence
times.
03
A “universal” set
of quantum
gates.
04
A qubit-
specific measur
ement capabilit
y.
05
The ability to
interconvert
stationary and
flying qubits.
06
The ability to
faithfully transmit
flying qubits
between
specified
locations.
07

29. QUANTUM
ALGORITHMS 1992
Deutsch–Jozsa algorithm
1994
Shor's algorithm
1996
Grover's algorithm

31. QUANTUM COMMUNICATION
SYSTEM
Exploits the
quantum nature of
objects to represent
information
Source, detector,
channel, the noise,
the eavesdropper, ..
and whole system
can have quantum
properties.
Information
representation
•current or voltage levels
•Spin of electron
•Polarisation or angular
momentum of photons
Channel:
Free space
gravitational waves

32. NO CLONING
THEOREM
IT IS IMPOSSIBLE TO
CREATE A COPY OF AN
UNKNOWN QUBIT !

33. HOW POSTULATES ARE CONNECTED
TO QUANTUM COMMUNICATION
1. Every measurement perturbs the system.
2. One cannot determine simultaneously the position and the
momentum of a particle with arbitrary high accuracy.
3. One cannot measure the polarization of a photon in the
vertical-horizontal basis and simultaneously in the diagonal
basis
4. One cannot draw pictures of individual quantum
processes.
5. One cannot duplicate an unknown quantum state.

34. CRYPTOGRAPHY
• Private Key Cryptography • Public Key Cryptography

35. QUANTUM
CRYPTOGRAPHY
• Quantum Key Distribution
• BB 84 Protocol
• E 91 protocol
• High Dimensional Key Distribution
• Device Independent Key
Distribution

36. QKD APPLICATION
BB84 PROTOCOL
IMPLEMENTED WITH
POLARIZATION OF
PHOTONS

37. QUANTUM ENTANGLEMENT
ENTANGLEMENT is like two people tossing a
coin at distant locations.
The outcome is completely random, but it
is the same outcome in both locations !!
• Non-local correlations exhibited by a set of qubits
• They cannot be expressed as product of 2 states

38. QUANTUM TELEPORTATION

39. HIGH
DIMENSIONAL
QUANTUM
COMMUNICATION
Encode
more
information
per
quantum
state
Use “Qudits”
instead of
“Qubits”
•Generalization
of Qubit into
d-state
systems

40. QUANTUM
SATELLITES
• Chinese Satellite
Micius I in 2016
• EU’s Eutelsat
Quantum in 2019
The Race
continues….
• Chinese Satellite
Micius II
• Canadian
QEYSSat

41. QUANTUM
INTERNET
• Just as two people can
communicate over the
Internet, a quantum
Internet based on
quantum repeater
technologies would
allow them to share
entanglement. This
shared resource would
then allow them to
communicate securely

42. TIMELINE
1981
Feynman
proposes the idea
of Quantum
computation
1984
First Quantum
communication
protocol by
Bennet and
Basard
1985
David Deutsch
develops the
Quantum
Computing
Model
1991
Artur Ekert’s
protocol using
quantum
entanglement as
resource
1994
Peter Shor
develops an
algorithm to
factor very large
numbers in
polynomial time
1997
Lov Grover
develops a
quantum search
algorithm
2000
Linear Optical
Quantum
Computation by
Knill, Laflamme
and Milburn
2016
China launches
first Quantum
Communication
satellite Micius-I
2017
First
Intercontinental
quantum safe
videocall
between China
and Austria
2018
Google
announces the
creation of a 72-
qubit quantum
chip, called
"Bristlecone”

43. WHEN CAN WE HAVE THEM?
QUANTUM COMPUTERS
• D Wave (2011, 2012, 2015)
• IBM (2016, 2017)
• Intel (2017)
• Google (2019)
• Microsoft (2018)
• Volkswagen (tied up with Google)
• Alibaba (2017)
• NASA (2012)
QUANTUM COMMUNICATION
• Quantum Communications Chinese
Satellite Micius I
(August 2016)
• Quantum Internet (2020)

44. THANK YOU !