A brief description on the basic working of Quantum computers ,it's applications and future prospects.

1. Student Seminar Series.

2. Introduction..
area of study focused on developing computer technology based on the pri
um computers are different from digital electronic computers based on trans

3. Why Quantum computer..
 Gordon Moore, Intel Co-
founder said that the number
of transistors economically
crammed into a single
computer chip was doubling
every two years.
 Transistor cannot be made
smaller due to the laws of
Quantum mechanics starts to
take over.

4. History.
1982 - Feynman proposed the idea of creating machines based on the l
1985 - David Deutsch developed the quantum Turing machine, showing
1994 - Peter Shor came up with a quantum algorithm to factor very large
1997 - Lov Grover develops a quantum search algorithm with O(√N) com

5. Concepts of QC..
Qu-bits.
Superposition.
Quantum entanglement.

6. Representation of Data - Qubits
A bit of data is represented by a single atom that is in one of
two states denoted by |0> and |1>. A single bit of this form is
known as a qubit
A physical implementation of a qubit could use the two energy
levels of an atom. An excited state representing |1> and a
ground state representing |0>.
Excited State
Ground State Nucleus
Light pulse
of
frequency λ
for time
interval tElectron
State |0> State |1>

7. Representation of Data - Superposition
A single qubit can be forced into a superposition of the two states
denoted by the addition of the state vectors:
|ψ> = α |0> + α |1>
Where α and α are complex numbers and |α | + | α | = 1
A qubit in superposition is in both of the
states |1> and |0 at the same time

8. Representation of Data - Superposition
Light pulse
of frequency
λ for time
interval t/2
State |0> State |0> + |1>
Consider a 3 bit qubit register. An equally weighted
superposition of all possible states would be denoted by:
|ψ> = |000> + |001> + . . . + |111>
1
√8
1
√8
1
√8

9. Data Retrieval
In general, an n qubit register can represent the numbers 0
through 2^n-1 simultaneously.
Sound too good to be true?…It is!
If we attempt to retrieve the values represented within a
superposition, the superposition randomly collapses to represent
just one of the original values.
In our equation: |ψ> = α |0> + α |1> , α represents the
probability of the superposition collapsing to |0>. The α’s are
called probability amplitudes. In a balanced superposition, α
= 1/√2 where n is the number of qubits.
1 2 1
n

10. Relationships among data - Entanglement
Entanglement is the ability of quantum
systems to exhibit correlations between states
within a superposition.
Imagine two qubits, each in the state |0> +
|1> (a superposition of the 0 and 1.) We can
entangle the two qubits such that the
measurement of one qubit is always
correlated to the measurement of the other
qubit.

12. Building a quantum
computer.
 A quantum computer is nothing like a classical computer in
design; transistors and diodes cannot be used.
 A new type of technology is needed, a technology that
enables 'qubits' to exist as coherent superposition of 0 and 1
states.

13. Due to the nature of quantum physics, the destruction of
information in a gate will cause heat to be evolved which can
destroy the superposition of qubits.
Operations on Qubits - Reversible Logic
A B C
0 0 0
0 1 0
1 0 0
1 1 1
Input Output
A
B
C In these 3 cases,
information is being
destroyed
Ex.
The AND Gate
This type of gate cannot be used. We must use
Quantum Gates.

14. Quantum Gates
 Quantum Gates are similar to classical gates, but do not have
a degenerate output. i.e. their original input state can be derived
from their output state, uniquely. They must be reversible.
This means that a deterministic computation can be performed
on a quantum computer only if it is reversible. Luckily, it has
been shown that any deterministic computation can be made
reversible.(Charles Bennet, 1973)

15. Quantum Gates - Hadamard
Simplest gate involves one qubit and is called a Hadamard
Gate (also known as a square-root of NOT gate.) Used to put
qubits into superposition.
H
State
|0>
State |0> +
|1>
H
State
|1>
Note: Two Hadamard gates used
in succession can be used as a
NOT gate

16. Quantum Gates - Controlled NOT
A gate which operates on two qubits is called a Controlled-
NOT (CN) Gate. If the bit on the control line is 1, invert the
bit on the target line.
A - Target
B - Control
A B A’ B’
0 0 0 0
0 1 1 1
1 0 1 0
1 1 0 1
Input Output
Note: The CN gate has a similar
behavior to the XOR gate with
some extra information to make it
reversible.
A’
B’

17. Example Operation - Multiplication By 2
Carry Bit
Carry
Bit
Ones
Bit
Carry
Bit
Ones
Bit
0 0 0 0
0 1 1 0
Input Output
Ones Bit
We can build a reversible logic circuit to calculate multiplication by
2 using CN gates arranged in the following manner:
H

18. Quantum Gates - Controlled Controlled NOT (CCN)
A - Target
B - Control 1
C - Control 2
A B C A’ B’ C’
0 0 0 0 0 0
0 0 1 0 0 1
0 1 0 0 1 0
0 1 1 1 1 1
1 0 0 1 0 0
1 0 1 1 0 1
1 1 0 1 1 0
1 1 1 0 1 1
Input Output
A’
B’
C’
A gate which operates on three qubits is called a Controlled
Controlled NOT (CCN) Gate. Iff the bits on both of the
control lines is 1,then the target bit is inverted.

19. A Universal Quantum Computer
The CCN gate has been shown to be a universal reversible
logic gate as it can be used as a NAND gate.
A - Target
B - Control 1
C - Control 2
A B C A’ B’ C’
0 0 0 0 0 0
0 0 1 0 0 1
0 1 0 0 1 0
0 1 1 1 1 1
1 0 0 1 0 0
1 0 1 1 0 1
1 1 0 1 1 0
1 1 1 0 1 1
Input OutputA’
B’
C’
When our target input is 1, our
target output is a result of a NAND
of B and C.

20. Quantum dots..
 It is one of the possible ways to produce quantum computers.
 A single electron trapped inside a cage of atoms.
 When the dot is exposed to a pulse of laser light of the right
wavelength & duration, the electron is raised to an excited state: a
second burst of laser light causes the electron to fall back to its
ground state.
 Ex: NOT gate

21. Quantum teleportation
Quantum teleportation is a technique used to
transfer information on a quantum level, usually
from one particle to another.
Its distinguishing feature is that it can transmit the
information present in a quantum superposition,
useful for quantum communication and
computation.

22. Quantum parallelism
It is the method in which a quantum computer is
able to perform two or more computations
simultaneously.
In classical computers, parallel computing is
performed by having several processors linked
together.
In a quantum computer, a single quantum
processor is able to perform multiple computations

23. Deutsch’s algorithm…
First ever produced Quantum algorithm.
Used an non-deterministic algorithm.
Given a black box quantum computer known as an oracle that
implements the function f:{0,1}^n ->{0,1}. In layman's terms, it takes
n-digit binary values as input and produces either a 0 or a 1 as output
for each such value. We are promised that the function is either
constant (0 on all inputs or 1 on all inputs) or balanced[3] (returns 1
for half of the input domain and 0 for the other half); the task then is
to determine if f is constant or balanced by using the oracle.

24. Shor’s algorithm..
quantum circuit which implements a modular arithmetic of this giant numbe
obtain some results which hen passed through a classical computer gives u

25. Grover’s algorithm..
Finds the location of an item in an in-ordered list.
O(sqrt(n)).

26. Applications

27. Quantum networking
One possible use of quantum computers is that of networking, both
intranet and internet.
Quantum teleportation using light beams may be able to carry a great
deal more information, enough perhaps to support practical
computing.
But the issue in this is, creating large enough beams of light in both
locations, sending and receiving, to send all of the data within a
reasonable amount of time.

28. Encryption
Current encryption methods work by factoring numbers.
Ex. 12=2*2*3.
Very easy to do for small numbers.
Current encryption numbers use over 400 digits in size.
Today’s computers would take about a billion years to factor
these numbers.
A quantum computer with a similar performance as modern
computers would need seconds.

29. Ultra-secure & Super-dense
Communications
It is possible to transmit information without a signal
path by using quantum teleportation.
There is no way to intercept the path and extract
information.
Ultra-secure communication is also possible by
super-dense information coding where quantum
bits can be used to allow more information to be
communicated per bit than the same number of
classical bits.

30. Molecular Simulations
A quantum computer can simulate physical processes of
quantum effects in real time.
Molecular simulations of chemical interactions.
Allows chemists and pharmacists to learn more about how
their products interact with each other, and with biological
processes.
Ex: How a drug may interact with a person’s metabolism or disease.

31. True Randomness
Classical computers do not have the ability to
generate true random numbers i.e. there is always
a cycle or a trend.
Quantum computers can generate true
randomness, thus give more veracity to programs
that need true randomness in their processing.

32. Need for Quantum
computers
Quantum computers work on an atomic level
That is roughly 200 times smaller than Intel’s brand new
45nm architecture.
A lot faster than classical computing.
Would be very useful in research and algorithm
computation.
Makes those computations possible which seem
impossible today.

33. Virtual reality..
nt computational technology limits the "reality" these devices will be able to
Augmented reality..

34. Current challenges..
Number of bits in a word.
12-qubit machines is the most advanced to date.
Difficulty with large words is, too much quantum interaction can
produce undesired results. Since all the atoms interact with each other.
Physical size of the machines.
Current machines are too large to be of practical use to everyday
society.
If these drawbacks could be overcome and if scientists could
control even 50 atoms, researchers claim that the computing
power of that computer would be more than the current
supercomputers.

35. Future prospects..
When processor components reach atomic scale,
Moore’s Law breaks down.
Quantum effects become important whether we want
them or not.
NP type problems could be solved in polynomial time.
But huge obstacles in building a practical quantum
computer!

36. Conclusion..
Quantum Computing could provide a radical change
in the way computation is performed.
The advantages of Quatum Computing lie in the
aspects of Quantum Mechanics that are peculiar to it,
most notably entanglement.
Classical Computers will be significantly larger than
Quantum Computers for the foreseeable future.
“FEYNMAN’S QUOTE”.

37. THANK YOU..!