Quantum information theory deals with integrating information theory with quantum mechanics by studying how information can be stored and retrieved from quantum systems. Quantum computing uses quantum physics and quantum bits (qubits) that can exist in superpositions of states to perform computations in parallel and solve problems like factoring prime numbers faster than classical computers. Key challenges for quantum computing include preventing decoherence and protecting fragile quantum states.

1. PREPARED BY:
FENNY THAKRAR

2. Quantum information theory is the study of
how to integrate information theory with
quantum mechanics, by studying how
information can be stored with (and
retrieved from) a quantum mechanical
system.

3. QUANTUM INFORMATION TECHNOLOGY
IS NOTHING BUT DEALING WITH
COMPUTERS USING QUANTUM
PHYSICS…
AND HENCE ITS ALSO CALLED
QUANTUM COMPUTING…

4.  Computation with coherent atomic-scale
dynamics.
 The behavior of a quantum computer is
governed by the laws of quantum
mechanics.

5.  In
quantum systems possibilities
count, even if they never happen! -like
particle theory.
 Eachof exponentially many possibilities
can be used to perform a part of a
computation at the same time.

6. Moore’s Law:
We hit the quantum level 2010~2020.
 Quantum computation is more powerful
than classical computation.
 More can be computed in less time—the
complexity classes are different!

7.  Digital
systems have – bit
 Quantum systems have – qubit
 The primary piece of information in quantum
information theory is the qubit, an analog to the
bit (1 or 0) in classical information theory.
 The two position states of a photon in a
Mach-Zehnder apparatus is just one
example of a quantum bit or qubit

8.  Theparticle can exist in a linear
combination or superposition of the two
paths
 This
concept is applied here using qubits for
computations.

9.  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.

10. The following quantum physics concepts are
used in Quantum Computing.
 superposition
 Interference(constructive & destructive)
 Coherence
 Entanglement

11.  Superposition is a principle of quantum
theory
 Theprinciple of superposition claims that
while we do not know what the state of any
object is, it is actually in all possible states
simultaneously.
 Mathematically, it refers to a property of
solutions to the Schrödinger equation

12.  In physics, interference is the phenomenon
in which two waves superpose each other to
form a resultant wave of greater or lower
amplitude.

13. In physics, coherence is a property of waves
that enables stationary (i.e. temporally and
spatially constant) interference.

14. Entanglement is a term used in quantum
theory to describe the way that particles of
energy/matter can become correlated to
predictably interact with each other
regardless of how far apart they are.

16. CRYPTOGRAPHY:-
Transmitting information with access
restricted to the intended recipient even if
the message is intercepted by others.

17. The process
• Sender Plaintext Key
Encryption
Secure
Cryptotext transmission
Decryption
Recipient Plaintext
Key ready for use
Message encryption
Secure key distribution
Hard Problem for conventional
encryption

18.  Encryption algorithm and related key are
kept secret.
 Breaking the system is hard due to large
numbers of possible keys.
 For example: for a key 128 bits long there
128 38
2 10 are keys to check
using brute force.
 The fundamental difficulty is key
distribution to parties
who want to exchange messages.

19.  In 1970s the Public Key Cryptography
emerged.
 Each user has two mutually inverse
keys.
 The encryption key is published;
 The decryption key is kept secret.
 Eg:- Anybody can send a message to Bob
but only Bob can read it.

20.  The most widely used PKC is the RSA algorithm
based on the difficulty of factoring a product
of two large primes.
 EASY PROBLEM:- Given two large primes p and
q and compute
n p q
 HARD PROBLEM:- Given n compute p and q.

21.  The best known conventional algorithm
requires the solution time proportional to:
1/ 3 2/3
T (n) exp[ c (ln n ) (ln ln n ) ]
 For p & q 65 digits long T(n) is approximately
one month using cluster of workstations
and
For p&q 200 digits long T(n) is astronomical.

22.  In 1994 Peter Shor from the AT&T Bell
Laboratory showed that in principle a
quantum computer could factor a very long
product of primes in seconds.
Shor’s algorithm time computational complexity
is 3
T (n) O [(ln n ) ]

23.  It solved THE KEY DISTRIBUTION problem.
 It unconditionally secured the key
distribution method proposed by Charles
Bennett and Gilles Brassard in 1984.
 The method is called BB84.

25.  This
makes impossible to intercept message
without being detected.

26.  Potential (benign) applications
- Faster combinatorial search
- Simulating quantum systems
 ‘Spinoff’in quantum optics, chemistry, etc.
 Makes QM accessible to non-physicists
 Surprising connections between physics and
CS
 New insight into mysteries of the quantum

27.  Key technical challenge:
prevent decoherence , or unwanted
interaction with environment.
 Approaches: NMR, ion trap, quantum dot,
Josephson junction, opticals,etc….