MIT scientists build world's first scalable quantum computer

Quantum computing now "much more an engineering effort, and not a basic physics question," claims MIT professor Isaac Chuang

Computer scientists at Massachusetts Institute of Technology (MIT) and the University of Innsbruck in Austria say that they have put together the first five quantum bits (or qubits) of a quantum computer, capable of executing simple mathematical challenges.

The device is being tested on solving mathematical-factoring problems, which could eventually have implications for applications that use factoring as the basis for encryption to keep information, such as credit cards and sensitive data, secure.

While the proof of concept has only been applied to the number 15, the researchers claim that theirs is the "first scalable implementation" of quantum computing to solve Shor's algorithm, a quantum algorithm devised by Morss Professor of Applied Mathematics at MIT Peter Shor.

Shor devised a quantum algorithm that can calculate the prime factors of a large number vastly more efficiently than a typical computer.

According to MIT, "the team was able to keep the quantum system stable by holding the atoms in an ion trap, where they removed an electron from each atom, thereby charging it. They then held each atom in place with an electric field".

Isaac Chuang, professor of physics, electrical engineering and computer science at MIT, added: "That way, we know exactly where that atom is in space. Then we do that with another atom, a few microns away - [a distance] about 100th the width of a human hair.

"By having a number of these atoms together, they can still interact with each other, because they're charged. That interaction lets us perform logic gates, which allow us to realise the primitives of the Shor factoring algorithm. The gates we perform can work on any of these kinds of atoms, no matter how large we make the system."

Chuang is a pioneer in the field of quantum computing. In 2001, he designed a quantum computer based on one molecule that could be held in 'superposition' and manipulated with nuclear magnetic resonance to factor the number 15. The results represented the first experimental realisation of Shor's algorithm. But the system wasn't scalable; it became more difficult to control the system as more atoms were added.

However, the architecture that Chuang and his team have put together is, he believes, highly scalable, and this scalability will enable them to build quantum computing devices capable of solving much bigger mathematical factors.

"It might still cost an enormous amount of money to build - you won't be building a quantum computer and putting it on your desktop any time soon - but now it's much more an engineering effort, and not a basic physics question," said Chuang.

Earlier this week, the UK government announced plans to invest some £200m in quantum computing research, as well as extra support for students.