PPT ON QUANTUM COMPUTING

CLICK HERE TO DOWNLOAD PPT ON QUANTUM COMPUTING

QUANTUM COMPUTING  Presentation Transcript

1.QUANTUM COMPUTING

2.Introduction History of Quantum Computing Quantum Computer Basics Implementation of Quantum Computing Applications of Quantum Computing Current progress Conclusion

3.INTRODUCTION A Quantum Computer is a computer that harnesses the power of atoms and molecules to perform memory and processing tasks. It has the potential to perform certain calculations billions of times faster than any silicon-based computer.

4.HISTORY1982 – First time Quantum Theory applied to computers 1989 – First Quantum Algorithm (Deutsch)? 1994 – Shor's Algorithm developed 1996 – Grover's Algorithm developed 1998 – 2-Qubit register developed 2001 – Shor's Algorithm ran on7 bit QC at Los Alamos labs May 2006 – Experimental 12-bit QC built.

5.QUANTUM COMPUTER BASICS n the classical model of a computer, the most fundamental building block, the bit, can only exist in one of two distinct states, a 0 or a 1. In a quantum computer the rules are changed qubit exist in the classical 0 , 1 state and coherent superposition of both. Two Universes Increasing the number of qubits therefore exponentially increases the 'quantum parallelism' we can obtain with the system.

6.A quantum computer is nothing like a classical computer in design; you can't for instance build one from transistors and diodes. In order to build one, a new type of technology is needed, a technology that enables 'qubits' to exist as coherent superpositions of 0 and 1 states. The best method of achieving this goal is still unknown, but many methods are being experimented with and are proving to have varying degrees of success.

7.IMPLEMENTATION OF QUANTUM COMPUTING Quantum Dots Computing liquids

8.QUANTUM DOTS An implementation of the qubit is the 'quantum dot' which is basically a single electron trapped inside a cage of atoms. When the dot is exposed to a pulse of laser light of precisely the right wavelength and 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. The ground and excited states of the electron can be thought of as the 0 and 1 states of the qubit and the application of the laser light can be regarded as a controlled NOT function as it knocks the qubit from 0 to 1 or from ' to 0. 9.PROBLEMS Unfortunately there are a number of practical problems that are preventing this from happening: The electron only remains in its excited state for about a microsecond before it falls to the ground state. Bearing in mind that the required duration of each laser pulse is around 1 nanosecond, there is a limit to the number of computational steps that can be made before information is lost. Constructing quantum dots is a very difficult process because they are so small. A typical quantum dot measures just 10 atoms (1 nanometer) across. The technology needed to build a computer from these dots doesn't yet exist.

10.COMPUTING LIQUIDS The latest development in quantum computing takes a radical new approach. It drops the assumption that the quantum medium has to be tiny and isolated from its surroundings and instead uses a sea of molecules to store the information. When held in a magnetic field, each nucleus within a molecule spins in a certain direction, which can be used to describe its state; spinning upwards can signify a 1 and spinning down, a 0.

11.Spinning of atoms can represent bits Spinning down represents 0 Spinning up represents 1 Spinning both ways is called a “super-position” These bits is called “qubits”

12.The quantum computer in this technique is the molecule itself and its qubits are the nuclei within the molecule. This technique does not however use a single molecule to perform the computations; it instead uses a whole 'mug' of liquid molecules. The advantage of this is that even though the molecules of the liquid bump into one another, the spin states of the nuclei within each molecule remain unchanged. Decoherence is still a problem, but the time before the decoherence sets in is much longer than in any other technique so far.

13.APPLICATION Shor’s Algorithm: This is an algorithm invented by Peter Shor in 1995 that can be used to quickly factories large numbers. If it is ever implemented it will have a profound effect on cryptography, as it would compromise the security provided by public key encryption (such as RSA).

14.STAGE I The first stage of the algorithm is to place a memory register into a coherent superposition of all its possible states. The letter 'Q' will be used denote a qubit that is in the coherent state. A calculation performed on the register can be thought of as a whole group of calculations performed in parallel, one in each universe. In effect, a calculation performed on the register is a calculation performed on every possible value that register can represent.

15.STAGE II The second stage of the algorithm performs a calculation using the register. The details of which are as follows: The number N is the number we wish to factorise, N = 15 A random number X is chosen, where 1 < X < N-1 X is raised to the power contained in the register (register A) and then divided by N The remainder from this operation is placed in a second 4 bit register (register B).

16.After this operation has been performed, register B contains the superposition of each universes results.

17.Notice that the contents of register B follows a repeating sequence (1,2,4,8,1,2,4,8...), the frequency at which this repeats can be named f. In this case the repeating sequence (1, 2, 4, 8) has four values so f = 4.

18.STAGE III The frequency of repetition, f, can be found. This is done by performing a complex operation on register B and then looking at its contents which causes the results from every universe to interfere with each other.

19.CAN THE RESULT BE GUARANTEED? The resulting number cannot be guaranteed to be a prime factor, but there is a good chance that it is one. The interference that produces the value for f tends to favour the correct answer as incorrect answers cancel each other out. In our example the value f = 4 does give a correct answer of 3. The fact that the answer cannot be guaranteed to be correct is of little consequence as it can be easily checked with multiplication. If the answer is incorrect, there is a very strong chance that repeating the calculation a few times with different values of X will produce the right answer.

20.CURRENT PROGRESS 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.