# A brief guide to quantum computing…

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You may have noticed that when it comes to technology, things just keep getting smaller and faster. A smaller doodah here, a thinner whatsit there. Almost every week you hear of some new gadget boasting greater processing power and more memory than any normal person could use. All this in a “pocket sized” device you could fit up a nostril. The reason your state of the art smartphone can be made so compact is that in each new generation of technology come smaller, faster versions of the components that went before. Our culture’s hunger for faster computing power fuels this process, demanding the miniaturization of components so that more can be done with the technology we have. But where is the limit? How minute can things get before they no longer function, and what effect will this have on the future of technology itself?

You’ll be glad to hear the answer is not rocket science. But it is quantum mechanics, which strikes as much fear into the hearts of the masses as a zombie apocalypse. But, fear not dear reader, for the ideas behind it are both straightforward and fascinating. Even your run-of-the-mill, brain-thirsty Undead would grasp the basics.

To begin with, classical electronic components (i.e. current silicon based devices) will soon be reaching their fundamental limit as miniaturization forces them towards the size of atoms. At this scale quantum mechanics rules all and will do its best to prevent classical processes (our computers’ electronic operations) taking place. So, instead of trying to fight these irritating quantum effects, scientists, heavily funded by the likes of Nokia, Toshiba and countless defence agencies, are working on ways to embrace and exploit the laws of quantum mechanics to perform their own computations. Enter the field of quantum computing.

Although still in its infancy, quantum computing has already made significant steps toward the realisation of quantum technologies. Quantum bits, or qubits (quantum particles such as photons), are used to represent data, and predictable quantum phenomena are employed to perform operations on these data. We are all familiar with classical computer bits existing as either 1 or 0, representing on or off, but what makes quantum computing so special is that qubits can exist as both 1 and 0 simultaneously. The laws of quantum mechanics have no problem with this just as long as the particle is not observed (measured). Once a qubit is observed it is forced to be in just one of these states.

This phenomenon can be visualized using Schrodinger’s Cat experiment, a thought experiment whereby a cat (we’ll call him Martin) is locked in a room where he has a 50/50 chance of being alive/dead at any given time. Let’s say this room is windowless and soundproof, and the 50% chance of death manifests itself as a revolver, with half its chambers full, sitting in Martins lap. Martin has left no suicide note, and no information (sound or sight of gunshot) leaves the room, so at any given time there is no way of telling if Martin has blown his furry little face off or not. Therefore, Martin is said to be both alive and dead (1 and 0). You may protest and say that Martin would never take his own life, he had so much to live for, but quantum physics doesn’t care. In its eyes Martin is both dead and alive until you prove otherwise by opening the door to find out.

This property has led to the first ever commercial application of quantum technology known as Quantum Key Distribution (QKD), which ensures secure communication between participants, by the laws of physics. As soon as an eavesdropper tries to listen in on (measure) the communication, the state of the transmission becomes defined, alerting the participants to the eavesdropper.

One of the driving forces behind the research is to achieve a full scale quantum computer. Basic devices have already been built that can perform certain calculations. The most notable of these are devices that can solve Shor’s algorithm (a method of factorizing large numbers, a calculation once thought to be computationally unfeasible), and a quantum computer that can solve a Sudoku puzzle. Although these devices are definitely quantum, they still require a lot of equipment (qubit generators and detectors) and extremely controlled environments (low noise, low light and precision alignment of components), for them to work. As a result they are not yet scalable for use in a quantum computer, and won’t be until a fully integrated device (one containing multiple elements all working together) can be achieved.

In theory, each qubit can be used in more than one operation at any given time, a property that increases rapidly with the number of qubits in a system. So, for example, a device containing two qubits could run four calculations simultaneously. A computer containing twenty qubits could run over a million, and a 1000-quibit device could process more simultaneous calculations than there are particles in the observable universe. As a result, large-scale quantum computers have the potential to solve problems, or carry out database searches, much faster than any current computer.

So, although a complete quantum computer is still a decade or so off, quantum computers look set to become the next big technological advance in our history, propelling us into a new era of accelerated computing power.

This shit’s gonna be big…or small.

#### Glossary:

Quantum mechanics – The theory mathematically explaining interactions and effects of particles primarily at the atomic and subatomic scales

Quantum particle – a fundamental particle which is subject to the laws of quantum mechanics i.e. electrons, photons

Photons – Particles/Packets of light energy

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