The Development Quantum Computing Essay Example for Free

The Development Quantum Computing Essay The story of computers started with the abacus invented by the Babylonians around 500 B. C. In 1614 John Napier began to develop mechanical computers such as the Babbage differential engine that could carry out one fixed problem to the accuracy of 20 decimal places using steam power. This is a picture of the left side of the Manchester Mark 1 computer, which was constructed in 1947. However, computing didnt advance until the introduction of vacuum tube powering in the early 20th century and transistors in 1947. At present computers work by manipulating bits, that can only be of discrete values of 1 or 0. In a digital computer the value of a bit is generated by the voltage on a capacitor, with a charged capacitor representing 1 and an uncharged capacitor denoting 0. According to Moores law the number of transistors in computer chips doubles every 18 months and computers have been seen to double in speed and half in size every two years, this is due to advanced lithography that allows wires and transistors contained in chips to be one hundredth of the width of a human hair These computers can carry out calculations using algorithms, a precise set of instructions used to solve a particular problem, an example of a fast or usable algorithm is addition and a slow or hard algorithm is factorisation. There a limits to present computers, that cant seem to be overcome by present technology. Hard algorithms like factorisation increase in time taken to solve exponentially when the number of digits increase, factorising a 400 digit number would take the most technologically advanced computer a billion years to perform. Computers have also reached their present size boundaries as transistors and wires cant be decreased to less than a width of an atom. (Approximately 10? 10 meters) The dawn of quantum computers In 1982 Richard Feynman began to consider the idea of quantum computers and in 1985 a revolutionary paper was published by David Deutsch of Oxford university, describing a universal quantum computer, however a use for quantum computers couldnt be found, until 1994 when Peter Shor from ATTs Bells laboratories devised a quantum algorithm that could theoretically perform efficient factorisation, creating a killer application for quantum computers for their great potential to break complex codes, for example electronic bank accounts, which gain their security from the present difficulty in factorising large numbers. What a Quantum computer can do for you In order to continue the advance in computing a new type of technology needed to be exploited. According to quantum physics a subatomic particle cant be said to exist, there are only probabilities of its existence and position until its definite state and position is discovered, then its probabilities collapse. Quantum physics breaks down the classically binary nature of a bit, with the invention of a quantum bit or qubit that can exist in coherent superposition, i. e. as a 0, 1 or simultaneously as a 1 and 0, with a numerical coefficient representing the probability of each state. The qubit is represented by the nuclear spins of each individual atom, for example the change in energy state. When you perform a calculation using an electron existing in both states you are performing two calculations, when another superposed qubit is added four calculations can be performed at once and so on. This exponential increase means that the time taken to carry out calculations rapidly decreases. The time to carry out calculations also decreases as atoms change energy states far quicker than even the fastest computer processors. With only a few hundred qubits it is possible to represent more numbers than there are atoms in our universe. It also increases storage capacity exponentially, as N qubits can store 2 numbers at once. Imagine the qubits are atoms whose different electronic states can be controlled by a tuned laser; this will change their state allowing in only one computational step a calculation to be performed on 2 different input numbers encoded in coherent superpositions of N qubits. The actual space a quantum computer will take up will be significantly smaller than present day desk tops, allowing the further development of sophisticated, efficient palm held computers. This is because given the right calculation each qubit can take the place of an entire processor, meaning that 100 barium ions could take the place of 100 computer processors. Aside from computers quantum technology has developed rapidly in the last ten years. In June 2002 a team of Australian scientist were able to teleport a laser beam, causing it to disappear and be regenerated 3 ft away, the results are yet to be confirmed but if they are sound this development could in a matter of years be able to teleport actual objects significant distances. Nuclear Magnetic Resonance After Shors discovery quantum computing construction began in earnest, however due to the phenomena of decoherence no atom or photon, being the qubit, can be of an undetermined state after being detected, the probabilities collapse and its state becomes definite. This makes further calculations impossible as the exponential element of the qubit has been lost, causing it to behave as a regular analogous bit. In order to keep the coherence of the qubit the inner workings of a quantum computer must be separate from the outside environment to stop any interactions that may determine the state of the qubit from occurring, but also be accessible so that calculations can be carried out and results obtained. A solution was Nuclear Magnetic Resonance (NMR) a technique developed in the 1940s, which is widely used in medical imagery and chemistry. Experiments were carried out, during the mid 1990s and it was found using a classical fluid made of many (1023) selected molecules allowed each qubit to be represented by many molecules allowing interactions to take place between some of the molecules but still maintaining the coherence of the qubit. NMR treats the spins of qubits as tiny bar magnets that will line up when a magnetic field is applied, allowing manipulation of the qubits. Two alternative alignments are generated one parallel to the external field and one anti-parallel to the field, corresponding to two different quantum states. NMR procedures also use an oscillating electromagnetic field, which is specially selected according to the properties of the molecules used. This causes certain spins in the liquid to be rotated, causing them to perform the different calculations required. Example Hydrogen nuclei placed in a magnetic field of 10 tesla, change orientation at a frequency of 400 megahertz (radio frequency) Due to decoherence the pulse is only turned on for a few millionths of a second but can cause the spins to rotate by 180 degrees, a pulse half that length causes a 90 degree spin. This causes the spins to be of state 1 or 0 with equal probability. This causes the spin to rotate about the magnetic field, as shown in the image on the right. This rotation emits a weak radio signal, which is picked up by the NMR apparatus.