# Scientists built a new quantum computer. It’s made of five atoms and “self-destroys” after each use

beats difficult algorithm

Experts on quantum computing have broken through another barrier on the way to quantum computers we could actually use.

A team of scientists from Innsbruck university and MIT managed to build a functional quantum computer that is the first to successfully scale the famous Shor algorithm for quantum computers.

Their newest pride and joy is only five atoms large and needs to be rebuilt after every use. However, the scientists claim that it is easily scalable – so an effort to build a larger and more complex quantum computer is no longer a question of taming the physics, but of a budget.

The newly built computer managed to solve one of the toughest computing problems – integer factorization. The decomposition of a composite number is fairly trivial for small numbers – i.e. we can easily calculate that 21 decomposed to seven times three – however, as the number we want to factorize grows larger, the task gets significantly more difficult for both humans and computers alike.

Factorization through standard computing is immensely difficult task. The most efficient algorithms can achieve only exponential complexity. That means that as the numbers of the digits in the number grows, the time needed to find the right factors grows exponentially. To give you an idea – in 2009, a group of experts managed to finish factorizing a number of 232 digits (768 bits of data) by employing hundreds of standard computers.

Their effort took two years.

If they tried to factorize a number that was just a few dozens of digits longer (with 1024 bits), their task would be about a thousand times more difficult.

### Quantum computers offer a whole new perspective

However, there is a more efficient way around this. It’s an algorithm published in 1994 by an MIT professor Peter Shor. It does have a tiny catch.

It needs a quantum computer for it to work.

Efficient factorization of large integer numbers can only be achieved thanks to some special attributes of quantum computers.

And this impressive algorithm is just the one that’s been demonstrated by the team of scientists mentioned and their quantum computer with 7 qubits and 4 “caching” qubits.

### How do quantum computers work?

Quantum computers work because of **qubits**. These are a unit of quantum information that is only remotely similar to a standard computing bit. There are many differences between the two, but the key distinction is the state qubits can be in. Where a classic bit can only be in a state of zero or one – and as such is similar to an on/off light switch – a qubit can do much more. Apart from states of zero and one, it can also be in a superposition of both – simply said “somewhere in between”. However, it’s not just a third state (like, say, 0, 1 and 2), but more of a probability of both states. It’s this very attribute that is key for quantum computing to work – it allows, for example, an easy parallelization of processes. At the same time, it is a reason quantum computers have many practical limitations – like the impossibility of debugging of code after the algorithm has been first put in.

So which difficult and large number did the scientists manage to factorize?

Fifteen.

However, the major benefit of their work is not the trivial result that we could probably all arrive to in our heads, but a demonstration of how it is possible to practically run Shor’s algorithm and scale the process upwards.

Their product shares limitations with all the other experiments in quantum computing. The algorithm cannot be altered or debugged after the initial setup and reading the result effectively “destroys” the computer, so it needs to be “built” again. Even so, it’s very probably that with time, experts will manage to work around these limitations.

### The future looks bright for quantum computing

The breakthrough quantum computer was physically constructed out of only five atoms held in an ion trap, lasers that relayed information and lots of other equipment, for supercooling the whole thing etc. It was by no means a simple endeavour that could be tucked away beneath our desks in the foreseeable future.

It is still a huge step forward for researchers and science that could eventually matter even for regular IT hardware. In the nearest future, we will probably see further attempts to break records at factorization through quantum means – the last one from 2014 is held by scientists from Kyoto and Oxford, whose quantum computer managed to factorize the number 56 153 with 4 qubits and a minimization algorithm.

One of the unintended consequences of the gains in quantum computing will be a need to change a perspective on IT security. Experts will have to come up with new models of security, because most of current approached to security are to some extent based on the practical difficulty of factorization. Quantum computers are inherently more effective at this task though, which could mean that security measures could be broken by actors who will have access to these machines.