 Open Access
 Total Downloads : 19
 Authors : Lokesh Saini, Ravi Shankar Dayanand
 Paper ID : IJERTCONV5IS10031
 Volume & Issue : ICCCS – 2017 (Volume 5 – Issue 10)
 Published (First Online): 24042018
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Quantum Computers – an Approach to Reduce Time Complexity?
Lokesh Saini Ravi Shankar Dayanand

ech Student B.Tech Student Assistant Professor
Dept. of CSE Dept. of CSE Dept. of CSE
HMRITM New Delhi, India
HMRITM New Delhi, India
HMRITM New Delhi, India
AbstractQuantum computers are the outcome of upgraded technology used to remove time complexity. Quantum computers are expert in its own the field which investigates computational and other properties of computer based on mechanical principles. In quantum computers important objective is to find quantum algorithms that are significantly faster than classical algorithms. Here we give a brief introduction to quantum computers considering some physical system that can be i N different mutually exclusive classical states. Call these states 1i,2i,… ,Ni. Classical states .A pure quantum state is a superposition of classical states, written i = 11i+ 22i+Â·Â·Â·+ NNi [1].
Keywords: Quantum Computers, Classical Computers, High Performance.

INTRODUCTION
Quantum computing or computation systems [quantum computers] that make direct use of quantum mechanical phenomena, such as superposition and entanglement, such as to perform operation on data.
Quantum computer are different from binary digital computer system [electronic computer based on transistors].Whereas common digital computing requires that the data be encoded into binary digits
(bits),each of which is always in one of two definite states[0 or 1],quantum computer use quantum bits, which can be superposition of state , A quantum Turing machine is theoretical model of such a computer ,and is known as the universal quantum computer.
The field of quantum computing was initialize by the work of Paul Benioff and Yuri manin in 1980, Richard Feynman in 1982, and David Deutsch in 1985. Quantum Computer, a computer that uses the effect of quantum mechanics to its advantage.
Fig.1.1
A computer which makes use of that Quantum states of subatomic particles to store information. Recent development of quantum computer have bought the idea to everybody attention. One such development was the invention of an algorithm to factor large number on a quantum computer by peter shor[Bell Laboratories].By using this algorithm, a quantum computer would be able to crack codes much more quickly than other
ordinary(or classical) computer could. In fact a quantum computer capable of performing shorts algorithms would be able to break current cryptography techniques in a matter of seconds. With the motivation provided by this algorithm the topic of quantum computing has gathered momentum and researches around the world are racing to be the first create a practical quantum computer .As we are in 2017, the development of actual quantum computer is till infancy, but experiments have been carried out in which quantum computational operations were executed on a very small number of quantum bits.
Both practical and theoretical research continues, and many national government and military agencies are funding quantum computing research in an effort to develop quantum computers for civilian, business, trade, environment and national security purpose, such as cryptanalysis.

CONCEPTS OF QUANTUM COMPUTERS
Qubit
Fig.1.2
A quantum bit or qubit is a unit of quantum information.
Many different physical objects can be used as qubits such as atoms, photons, or electrons.
Exists as a 0, a 1 or simultaneously as a superposition of both 0 & 1
Quantum information
Quantum information is physical information that is held in the "state" of a quantum system.
Though the amount of information that can be retrieved in a single qubit is equal to one bit, the difference lies in the processing of information
Quantum entanglement
In Quantum Mechanics, it sometimes occurs that a measurement of one particle will effect the state of another particle, even though classically there is no direct interaction.
When this happens, the state of the two particles is said to be entangled.
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>.
Fig.1.2
Need for Quantum computers
Future prospects
Fig.1.3
Quantum computers work on an atomic level that is roughly 200 times smaller than Intels brand new 45nm architecture.
Would be very useful in research and algorithm computation
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.
Fig.1.1
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
When processor components reach atomic scale, Moores Law breaks down

Quantum effects become important whether we want them or not
But huge obstacles in building a practical quantum
computer!


BACKGROUND OF QUANTUM COMPUTER


1982:Feynman proposed the idea of creating machines based on the law of quantum mechanics instead of the law of classical physics.

1985:David Deutsch developed the quantum turing machine, shwing that quantum circuits are universal.

1994:Peter Shor came up with a quantum algorithm to factor very large numbers in polynomial time.

1997:Lov Grover develops a quantum search algorithms with O(N) complexity.


APPLICATIONS OF QUANTUM COMPUTER

Cryptography: Cryptography is a cornerstone of information security. It is used to encode and decode data in order to fulfill the requirement for confidentiality, integrity, authentication as well as nonrepudiation. Together, these are frequently referred to as cryptography services.
Fig.1.4

Artificial intelligence: Over the past few decades, quantum effects have greatly improved many areas of information science, including computing, cryptography, and secure communication.
Fig.1.5

Teleportation: Quantum teleportation relies on something called an entangled state.

Quantum communication: In quantum communication via noisy channels, the error probability scales exponentially with the length of the channel. We present a scheme of a quantum repeater that overcomes this limitation.


SHORS ALGORITHM
Shors algorithm shows (in principle,) that a quantum computer is capable of factoring very large numbers in polynomial time. The algorithm is dependant on

Modular Arithmetic

Quantum Parallelism

Quantum Fourier Transform
Shors Algorithm Periodicity

An important result from Number Theory: F(a) = x mod N is a periodic function

Choose N = 15 and x = 7 and we get the following:

7 mod 15 = 1

7 mod 15 = 7

7 mod 15 = 4

7 mod 15 = 13

7 mod 15 = 1

Shors Algorithm – In Depth Analysis
To Factor an odd integer N (Lets choose 15) :

Choose an integer q such that N < q < 2N lets pick 256

Choose a random integer x such that GCD(x, N) = 1 lets pick 7

Create two quantum registers (these registers must also be entangled so that the collapse of the input register corresponds to the collapse of the output register)

Input register: must contain enough qubits to represent numbers as large as q1. up to 255, so we need 8 qubits

Output register: must contain enough qubits to represent numbers as large as N1. up to 14, so we need 4 qubits



CONCLUSION:

To conclude the study, we found that the concept of quantum computers is upcoming concepts of high performance quantum computer. [1]Many research groups have discovered qubit and quantum computers as discussed in literature. Practical quantum computers are expected to give better results in comparison to classical computer that operates on a practically large number of qubits[2]. The research of quantum computer is very limited in literature and the concept is in its novel stage which requires more attention. This sector needs more architectural solutions or algorithms to advancement to make this concept usable in art for computational and logical reasoning [3].
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