Introduction Computer: The back bone of today’s world. Now a day, people are looking for a faster and small computers and this has lead to a new era in computer sciences that is quantum computing hence to the quantum computers. Quantum computer is a device for computation that makes direct use of some quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data.. The basic principle behind quantum computation is that quantum properties can be used to represent data and perform operations on these data. As Moore's Law states, the number of transistors on a microprocessor continues to double every 18 months, the year 2020 or 2030 will find the circuits on a microprocessor measured on an atomic scale. And the logical next step will be to create quantum computers, which will harness the power of atoms and molecules to perform
memory and processing tasks. Quantum computers have the potential to perform certain calculations significantly faster than any siliconbased computer.
Basis: A classical computer has a memory made up of bits, where each bit represents either a one or a zero. A quantum computer maintains a sequence of qubits. Today's computers work by manipulating bits that exist in one of two states: a 0 or a 1. Quantum computers aren't limited to two states; they encode information as quantum bits, or qubits, which can exist in superposition. This superposition of qubits is what gives quantum computers their inherent parallelism. This parallelism allows a quantum computer to work on a million computations at once, while your desktop PC works on one. Qubits represent atoms, ions, photons or electrons and their respective
control devices that are working together to act as computer memory and a processor. Because a quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today's most powerful supercomputers. A quantum computer operates by manipulating those qubits with a fixed sequence of quantum logic gates. The sequence of gates to be applied is called a quantum algorithm.
The Potential and Power of Quantum Computing: In a traditional computer, information is encoded in a series of bits, and these bits are manipulated via Boolean logic gates arranged in succession to produce an end result. Similarly, a quantum computer manipulates qubits by executing a series of quantum gates, each a unitary transformation acting on a single qubit or pair of qubits. In applying these gates in succession, a quantum
computer can perform a complicated unitary transformation to a set of qubits in some initial state. The qubits can then be measured, with this measurement serving as the final computational result. This similarity in calculation between a classical and quantum computer affords that in theory, a classical computer can accurately simulate a quantum computer. In other words, a classical computer would be able to do anything a quantum computer can. So why bother with quantum computers? Although a classical computer can theoretically simulate a quantum computer, it is incredibly inefficient, so much so that a classical computer is effectively incapable of performing many tasks that a quantum computer could perform with ease. The simulation of a quantum computer on a classical one is a computationally hard problem because the correlations among quantum bits are qualitatively different from correlations among classical bits, as first explained by John Bell.
Take for example a system of only a few hundred qubits, that in simulation would require a classical computer to work with exponentially large matrices (to perform calculations on each individual state, which is also represented as a matrix), meaning it would take an exponentially longer time than even a primitive quantum computer. Richard Feynman was among the first to recognize the potential in quantum superposition for solving such problems much faster. For example, a system of 500 qubits, which is impossible to simulate classically, represents a quantum superposition of as many as 2500 states. Each state would be classically equivalent to a single list of 500 1's and 0's. Any quantum operation on that system --a particular pulse of radio waves, for instance, whose action might be to execute a controlled-NOT operation on the 100th and 101st qubits--, would simultaneously operate on all 2500 states. Hence with one fell
swoop, one tick of the computer clock, a quantum operation could compute not just on one machine state, as serial computers do, but on 2500 machine states at once! Eventually, however, observing the system would cause it to collapse into a single quantum state corresponding to a single answer, a single list of 500 1's and 0's, as dictated by the measurement axiom of quantum mechanics. The reason this is an exciting result is because this answer, derived from the massive quantum parallelism achieved through superposition, is the equivalent of performing the same operation on a classical super computer with ~10150 separate processors (which is of course impossible)!! Early investigators in this field were naturally excited by the potential of such immense computing power, and soon after realizing its potential, the hunt was on to find something interesting for a quantum computer to do. Peter
Shor, a research and computer scientist at AT&T's Bell Laboratories in New Jersey, provided such an application by devising the first quantum computer algorithm. Shor's algorithm harnesses the power of quantum superposition to rapidly factor very large numbers (on the order ~10200 digits and greater) in a matter of seconds. The premier application of a quantum computer capable of implementing this algorithm lies in the field of encryption, where one common (and best) encryption code, known as RSA, relies heavily on the difficulty of factoring very large composite numbers into their primes. A computer which can do this easily is naturally of great interest to numerous government agencies that use RSA -previously considered to be "unbreakable" -- and anyone interested in electronic and financial privacy. Encryption, however, is only one application of a quantum computer. In addition, Shor has put together a toolbox of mathematical operations that
can only be performed on a quantum computer, many of which he used in his factorization algorithm. Furthermore, Feynman asserted that a quantum computer could function as a kind of simulator for quantum physics, potentially opening the doors to many discoveries in the field. Currently the power and capability of a quantum computer is primarily theoretical speculation; the advent of the first fully functional quantum computer will undoubtedly bring many new and exciting applications. Integer factorization is believed to be computationally infeasible with an ordinary computer for large integers if they are the product of few prime numbers (e.g., products of two 300digit primes). By comparison, a quantum computer could efficiently solve this problem.. This ability would allow a quantum computer to decrypt many of the cryptographic systems in use today, in the sense that there would be a polynomial time (in the number of digits of the
integer) algorithm for solving the problem. In particular, most of the popular public key ciphers are based on the difficulty of factoring integers. These are used to protect secure Web pages, encrypted email, and many other types of data. Breaking these would have significant ramifications for electronic privacy and security.
Current prospects: The recent work on the 'computing liquid' technique pioneered by Dr. Gershenfield and Dr. Chuang (Los Alamos National Laboratory, New Mexico) has given quantum computing a promising future. In fact, Dr. Gershenfield believes that a quantum co-processor could be a reality within 10 years if the current pace of advancement continues. Other techniques, such as quantum dots, may also yield similar results as our technology advances. The optimist will point out that the problems being experienced by
researchers appear to be technical rather than fundamental. On the other side of the argument, is the topic of decoherence. This problem has not been resolved and many people, including Rolf Landauer of IBM's Thomas Watson Research Centre, believe that the quantum computer is unlikely to progress beyond the 10-qubit system (described above), as decoherence makes them too fragile to be practical. Researchers in quantum communication have enjoyed a greater level of success. The partial quantum computers involved have enabled secure communication over distances as far as 10km. Depending on how costly these lines are to develop and the demand that exists for them; there could be a strong future for quantum communications. The most advanced quantum computers have not gone beyond manipulating more than 16 qubits,
meaning that they are a far cry from practical application. However, the potential remains that quantum computers one day could perform, quickly and easily, calculations that are incredibly time-consuming on conventional computers. Several key advancements have been made in quantum computing in the last few years. Let's look at a few of the quantum computers that have been developed.
FUTURE OUTLOOK:
At present, quantum computers and quantum information technology remains in its pioneering stage. At this very moment obstacles are being surmounted that will provide the knowledge needed to thrust quantum computers up to their rightful position as the fastest computational machines in existence. Error correction has made promising progress to date, nearing a point now where we may have the tools required to build a computer robust enough to adequately withstand the effects of decoherence. Quantum hardware, on the other hand, remains an emerging field, but the work done thus far suggests that it will only be a matter time before we have devices large enough to test Shor's and other quantum algorithms. Thereby, quantum computers will emerge as the superior computational devices at the very least, and perhaps one day make today's modern computer obsolete. Quantum computation has its origins in highly specialized fields of theoretical physics, but its future
undoubtedly lies in the profound effect it will have on the lives of all mankind.
Challenges The main problem is that quantum superpositions are extremely vulnerable and any interactions with its environment will quickly cause errors, which degrade the performance of the computer. Quantum versions of error-correcting codes have been developed recently which to a large extent solve this problem in theory, but not yet in the brittle practice of the physical lab (let alone the brittle practice of our desktops). This is related to development of Quantum Information Theory-the quantum extension of classical information theory. CWI's group has contributed to this research, and to related notions of the information in individual quantum states: Quantum Kolmogorov Complexity.
Building large quantum computers presents formidable problems to experimental physicists reminiscent of the initial barriers to classical computing: unreliable components, physically large components, memory, organization, communication, programming. The theory of quantum mechanics is currently extended, partially by CWI research, in particular with respect to the algebraic analysis of ``quantum entanglement''--a vital notion in many quantum algorithms, apparently not yet thoroughly investigated in quantum theory.
Conclusion With classical computers gradually approaching their limit, the quantum computer promises to deliver a new level of computational power. With them comes a whole new theory of computation that incorporates the strange effects of quantum mechanics and considers every physical object to be some kind of quantum computer. A quantum computer thus has the theoretical capability of simulating any finite physical system and may even hold the key to creating an artificially intelligent computer. The quantum computers power to perform calculations across a multitude of parallel universes gives it the ability to quickly perform tasks that classical computers will never be able to practically achieve. This power can only be unleashed with the correct type of algorithm, a type of algorithm that is extremely difficult to formulate. Some algorithms have already been
invented; they are proving to have huge implications on the world of cryptography. This is because they enable the most commonly used cryptography techniques to be broken in a matter of seconds. For now at least, the world of cryptography is safe because the quantum computer is proving to be very difficult to implement. The very thing that makes them powerful, their reliance on quantum mechanics, also makes them extremely fragile. The most successful experiments only being able to add one and one together. Nobody can tell if the problems being experienced by researchers can be overcome, some like Dr. Gershenfield are hopeful that they can whilst others believe that the quantum computer will always be to fragile to be practical.
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CERTIFICATE
This is to certify that Ms. Shweta Bharti (Roll No. 2K9/EC/709), student of Electronics and Communication branch, fourth semester, has completed her project report titled ‘Quantum computers’ under my guidance successfully and has submitted the project report to me.
Mr. Devanand (Astt. Professor) E & C Dept.
Project Report On
“Quantum Computers”
Submitted By: Shweta Bharti 2K9/EC/709 Electronics & Communication Dept.
.
