*What they are, what they do, and what they mean for you*

What if you could make a computer powerful enough to process all the information in the universe?

This might seem like something torn straight from fiction, and up until recently, it was. However with the arrival of quantum computing, we are about to make it reality. Recent breakthroughs by Intel and Google have catapulted the technology into the news. We now have lab prototypes, Silicon Valley start-ups and a multi-billion dollar research industry. Hype is on the rise, and we are seemingly on the cusp of a quantum revolution so powerful that it will completely transform our world.

On the back of this sensationalism trails confusion. What exactly are these machines and how do they work? And, most importantly, how will they change the world in which we live?

At the most basic level, the difference between a standard computer and a quantum computer boils down to one thing: information storage. Information on standard computers is represented as **bits**– values of either 0 or 1, and these provide operational instructions for the computer.

This differs on quantum computers, as they store information on a physical level so microscopic that the normal laws of nature no longer apply. At this minuscule level, the laws of quantum mechanics take over and particles begin to behave in bizarre and unpredictable ways. As a result, these devices have an entirely different system of storing information: **qubits**, or rather, quantum bits**.**

Unlike the standard computer’s bit, which can have the value of **either** 0 **or** 1, a qubit can have the value of 0, 1 or **both** 0 and 1 at the same time**. **It can do this because of one of the fundamental (and most baffling) principles of quantum mechanics- quantum superposition, which is the idea that one particle can exist in multiple states at the same time. Put another way: imagine flipping a coin. In the world as we know it (and therefore the world of standard computing), you can only have one of two results: heads or tails. In the quantum world, the result can be heads **and** tails.

What does all of this this mean in practice? In short, the answer is speed. Because qubits can exist in multiple states at the same time, they are capable of running multiple calculations simultaneously. For example, a 1 qubit computer can conduct 2 calculations at the same time, a 2 qubit computer can conduct 4, and a 3 qubit computer can conduct 8- increasing exponentially. Operating under these rules, quantum computers bypass the “one-at-a-time” sequence of calculation that a classical computer is bound by. In the process, they become the ultimate multi-taskers.

To give you a taste of what that kind speed might look like in real terms, we can look back to 2015, when Google and Nasa partnered up to test an early prototype of a quantum computer called D-Wave 2X. Taking on a complex optimisation problem, D-Wave was able to work at a rate roughly 100 million times faster than a single core classical computer and produced a solution in seconds. Given the same problem, a standard laptop would have taken 10,000 years.

Given their potential for speed, it is easy to imagine a staggering range of possibilities and use cases for these machines. The current reality is slightly less glamorous. It is inaccurate to think of quantum computers as simply being “better” versions of classical computers. They won’t simply speed up *any* task run through them (although they may do that in some instances). They are, in fact, only suited to solving highly specific problems in certain contexts- but there’s still a lot to be excited about.

One possibility that has attracted a lot of fanfare lies in the field of medicine. Last year, IBM made headlines when they used their quantum computer to successfully simulate the molecular structure of beryllium hydride, the most complex molecule ever simulated on a quantum machine. This is a field of research which classical computers usually have extreme difficulty with, and even supercomputers struggle to cope with the vast range of atomic (and sometimes quantum) complexities presented by complex molecular structures. Quantum computers, on the other hand, are able to read and predict the behaviour of such molecules with ease, even at a minuscule level. This ability is significant not just in an academic context; it is precisely this process of simulating molecules that is currently used to produce new drugs and treatments for disease. Harnessing the power of quantum computing for this kind of research could lead to a revolution in the development of new medicines.

But while quantum computers might set in motion a new wave of scientific innovation, they may also give rise to significant challenges. One such potentially hazardous use case is the quantum computer’s ability to factorise extremely large numbers. While this might seem relatively harmless at first sight, it is already stirring up anxieties in banks and governments around the world. Modern day cryptography, which ensures the security of the majority of data worldwide, relies on complex mathematical problems- tied to factorisation- that classical computers have insufficient power to solve. Such problems, however, are no match for quantum computers, and the arrival of these machines could render modern methods of cryptography meaningless, leaving everything from our passwords and bank details to even state secrets extremely vulnerable, able to be hacked, stolen or misused in the blink of an eye.

Despite the rapid progress that has been made over the last few years, an extensive list of obstacles still remain, with hardware right at the top. Quantum computers are extremely delicate machines, and a highly specialised environment is required to produce the quantum state that gives qubits their special properties. For example, they must be cooled to near absolute zero (roughly the temperature of outer space) and are extremely sensitive to any kind of interference from electricity or temperature. As a result, today’s machines are highly unstable, and often only maintain their quantum states for just a few milliseconds before collapsing back into normality- hardly practical for regular use.

Alongside these hardware challenges marches an additional problem: a software deficit. Like a classical computer, quantum computers need software to function. However, this software has proved extremely challenging to create. We currently have very few effective algorithms for quantum computers, and without the right algorithms, they are essentially useless- like having a Mac without a power button or keyboard. There are some strides being made in this area (QuSoft, for example) but we would need to see vast advances in this field before widespread adoption becomes plausible. In other words, don’t expect to start “quoogling” any time soon.

So despite all the hype that has recently surrounded quantum computers, the reality is that now (and for the foreseeable future) they are nothing more than expensive corporate toys: glossy, futuristic and fascinating, but with limited practical applications and a hefty price tag attached. Is the quantum revolution just around the corner? Probably not. Does that mean you should forget about them? Absolutely not.