Neither Here nor There: The Age of Quantum Computing

By Shaun Morgan

This rather cryptic title is entirely appropriate for this month's article because we're going to dip a toe into the surreal world of quantum computing. I must add at the outset that such toe-dipping requires considerable courage – on the part of both reader and writer. However, it's not so much the technology that demands a robust constitution. Indeed, a working, practical, quantum computer will offer many exciting possibilities for the future. No, it's the reality-twisting quantum world that might test us. As such, I promise to keep it as comprehensible, and indeed factually accurate, as my own limited comprehension will allow.

So what has prompted my sudden urge to write an article about quantum computers? Well, scientists have been plugging away at the concept for many years – and I will attempt to explain what such a device is shortly – but have been bedevilled by technical hurdles that have impeded progress. However, the field is gathering pace and recent technological breakthroughs mean that quantum computers are edging ever closer to commercial reality – not that you'll be able to pop down to Currys this Christmas (or next, or the one after, etc.) and cart one home!

Okay, so if you can't go out to buy one today, is there any point in reading on? Yes there is. You see, quantum computers are going to transform life in the 21st century in the way that current computing technology transformed life in the 20th century. We're not talking about an incremental improvement in the performance of our current PCs, laptops, servers and portable devices, but a seismic shift in the way such devices work and perform. Think punch card reader versus IBM supercomputer, think horse and cart versus NASA Space Shuttle, think telegraph wires versus fibre optics.

Classical versus Quantum

This seismic shift in performance is made possible because quantum computers exploit the weirdness of quantum physics. In our everyday experience of the world we know that a light switch, for example, is either on or off – it can't be both at once. The computers we use today are fundamentally based on the physics of switches, called transistors, which sit at the heart of the modern computer processor. The position of a transistor is binary – in other words it's either off (0) or on (1). The change in position is interpreted as information 'bits' which are combined into larger groupings called bytes, megabytes, gigabytes, etc.

So, the processing power of our current computer technology is fundamentally limited to the number of transistors that produce binary 0s and 1s – hence the push to make transistors smaller to fit more onto the processor. There is, by the way, a theoretical limit to how small these transistors can be manufactured and therefore a limit to the processing power of this silicon based technology. However, predictions surrounding where that fundamental limit might lie have been repeatedly confounded by Moore's Law – this states that the performance of processors, and the density of transistors residing in processors, doubles every 18 months to two years. Nevertheless, this exponential improvement in performance cannot continue indefinitely.

So what if you could replace the basic building blocks of the processor, the transistors, with something that can produce quantum bits, or 'qubits': 0s, or 1s, or both simultaneously. In the quantum world it is entirely possible to be in both 'states' (i.e. on and off) at the same time – an effect known as superposition. Superposition also leads, bizarrely, to the possibility of being simultaneously alive and dead – search for 'Schrödinger's cat' to see what I mean.

Anyway, we digress. Quantum computers, use funky lasers and superconducting dots or ion traps (whatever they are!) to produce and manipulate 'qubits' (1s, 0s or a superposition of both). The additional state that simultaneously represents both 1 and 0 increases the information storage capacity of the system before we even get going with any calculation.

But there's more. These qubits can be 'entangled' with other qubits to increase the overall processing capacity of the system. It is, according to New Scientist magazine, the combination of superposition and entanglement that gives quantum computers their awesome computational capabilities. If only we knew how to scale-up the techniques perfected in the laboratory to create a practical computer for the home.

Decoherence

If this article lacks coherence thus far, spare a thought for our potential quantum computer, which is particularly susceptible to decoherence – slight disturbances that wipe away the quantum effects. It is one key reason we can't nip down to the local electronics store and buy a quantum computer. The slightest encroachment of the outside environment completely destroys the delicate quantum state needed to perform the calculations. Any current quantum computer purchase would therefore require a room sized cryogenic refrigeration system to keep the temperature around minus 270ish degrees Celsius. Neither an affordable nor appealing proposition really.

Why the big deal?

Now we know that quantum computers are fundamentally different to our existing devices, we might well ponder their potential future application. Our current technology basically processes one instruction at a time – i.e. sequentially, in serial. And although our serial computers can be arranged to process information in parallel, quantum computers are inherently parallel processing devices – they can conduct multiple calculations simultaneously.

As such, new and intelligent ways to search large databases and the web will become possible. For example, Robert Schoelkopf, a scientist writing for eScienceNews, says that you'd be able to simultaneously test a set of, say, four phone numbers in search of a friend: "It's like being able to place one phone call that simultaneously tests all four numbers, but only goes through to the right one".

Scientists are also predicting the creation of new super secure communication and encryption systems. Many future possibilities flirt with the realm of science fiction. For example, a scientist by the name of WenShin Chen predicts the possibility of quantum teleportation a la Star Trek, although I have to say, others have firmly ruled out this possibility.

One day...

So while the basic components for a quantum computer have been created and tested, a practical, everyday device remains a distant goal I'm sorry to say. But the quest to bring supercomputer processing power to a desktop size machine is so alluring – especially for military and government purposes – that the next big breakthrough might be just around the corner.

So quantum computing is, as the title of the article suggested, neither here nor there, as an immediate prospect. We should bear in mind however the speed at which our current devices shrank and developed into the familiar consumer products all around us today. I'm not however holding my breath, but I am hoping to get my hands on one... one day.