# The Development Quantum Computing.

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Introduction

The Development Quantum Computing

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In the beginning

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 didn’t 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 can’t seem to be overcome by present technology.

Middle

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 Shor’s 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.

Conclusion

This demonstrates another quality of quantum computers NOT gates, which can operate on a combination of seemingly incompatible information. Classical computers require two input gates as well as a simpler NOT gate to perform similar operations on classically compatible inputs.

Alternatives to NMR

Ions seem to be the answer to NMR’s problems. There energy states can be determined using light and they can be controlled, by laser super cooling to micro Kelvin temperatures and positioned in ultra-high vacuum by electromagnetic forces that carefully control their 2 dimensional positions but allow 3 dimensional movement.

Limits to Quantum Computing

It is unlikely that quantum computers will ever be completely commercially viable and may only ever be used by big corporations using the factorisation algorithm. This is because the quantum computer is not suited to word processing, design programmes, or any form of internet and email jobs. However it is suited to large scale cryptography and constructing and efficiently searching large scale computers. At present it will be difficult to build a quantum computer of any size as the more qubits interacting the harder it is to control and stop the qubits dissipating useful information to the surrounding environment. There are also technical issues of working on a sub-atomic and single-photon scale.

This student written piece of work is one of many that can be found in our AS and A Level Modern Physics section.

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