## Quantum computers : you’ve probably heard of them already without really knowing what the fuss was all about. While these machines promise revolutionary changes in the technology world, they’re still far from being market-ready.

Computers as we know them are about to reach the limit of their capacity. And what do you do when something is not good enough anymore ? You create a new, more powerful version of the same thing. That’s how quantum computers were born. Thanks to quantum physics, scientists have been able to create a computer capable of using these principles to efficiently perform computations that conventional computers struggle to execute.

Some parts of these machines are almost as small as an atom. Transistors — the electric switch allowing the electric current to flow — are now as small as 14 nanometers. This is five hundred times smaller than a red blood cell. These computers parts are so small they can obey quantum physics principles.

### What’s the fuss about ?

First, let’s go back to traditional computers, where information is encoded in binary form. Each piece of information is called a bit, which can either be 1 or 0. Since computers are powered by electricity, 1’s and 0’s represent two possible states of an electrical circuit : 1 means that the circuit is closed and that electric current is flowing, and 0 means that the circuit is open.

In order to make a sequence of bits useful, computers must be able to transform a sequence according to some predefined rules. In conventional computers, this is done by applying a series of *instructions* to the bit-sequence. At the lowest levels of hardware, instructions are composed of physical circuits that apply very simple changes. These circuits, called *logic gates*, do things like comparing two bits to see if they’re equal, “flipping” a bit (i.e.: turn a 0 into a 1 or and a 1 into a 0), as well as more exotic operations like XOR. Grouping several hundreds of millions of logic gates onto a single piece of silicon produces a *microprocessor*.

In quantum computers, things get weird. Quantum bits (called qubits) are special nanometer-scale circuits that exhibit certain quantum properties. Firstly, a qbit occupies both the 0 and 1 state simultaneously, until its value is measured. When one actually “reads” a qbit, it will *collapse* into either a 0 or a 1, with a certain probability.

Secondly qbits exhibit *quantum entanglement*, which means the probability of collapsing into a given state (0 or 1) depends on the quantum value of *other* qubits. An interesting aside: quantum entanglement doesn’t seem to care about distance, so you could (in theory) entangle two particles at opposite ends of the galaxy, and change in the state of one particle would be instantaneously reflected in its partner.

Now comes the hat-trick. By carefully entangling multiple qbits together, a quantum computer can provoke a collapse whose final, measured configuration is overwhelmingly likely to solve a particular equation. Stated differently, the final *resting state* of the qbits will be that of the lowest-energy configuration, constrained by the equation the computer is solving.

If you’ve seen the movie K-PAX, you already have an intuition for how this works.

Still don’t get it ? Basically, quantum computers can solve certain complex equations near-instantaneously because rather than going through the calculations necessary to derive a solution (as with conventional computers), they exploit certain properties of physics to “mould” a set of qubits into the correct answer. Frédéric Allard, CTO at IBM France, explains that here “we are able to process calculations simultaneously, wherein a binary model we process them sequentially,” as traditional computers do not have superposition properties.

Embryos of quantum computers have been used since 2011. A Canadian-based company, D-Wave Systems made headlines when it announced that is was the world’s first company able to sell quantum computers.

To this day, tech companies, such as Google and IBM are all competing to achieve quantum supremacy and to be the first one to exceed the skills and power of a conventional computer. A 40 qubits computer would have the same power of the biggest computer in the world. IBM is planning on releasing a processor of 50 qubits in 2019.

### Endless possibilities for the future

If there’s one thing to remember, it’s that quantum computers won’t magically make every computation faster. Still, for certain types of problems, quantum computers represent an unspeakably large disruption. * *One example concerns the possibility of factoring large integers. In simple words, this represents the decomposition of an integer into a product of prime numbers. Right now, factoring any number beyond a handful of digits is completely intractable requires more computation time than the age of the universe itself, but with quantum computers, the qbits will simply collapse into the number’s constituent primes.

Why does this matter? In a word: cryptography. Banks, the Internet, credit-card payment terminals, website logins, email and electronic voting machines are all vitally dependent on the computational difficulty of factoring primes.

As of today, keeping a secret on the internet involves a kind of cryptography that quantum computers will render obsolete in an instant. Thankfully, quantum encryption is a vibrant (if fledgling) area of computer science research.

It’s not all bad news, though. In medical research, for instance, these new machines could accelerate numerous innovations and advances, especially when it comes to synthesizing complex proteins. “We’ll be able to find the best possible combinations of molecules in pharmaceuticals, find better material alloys, or even unravel security codes,” said Allard.