Counting qubits: computing at the edge of reality

Scientists in America are celebrating an exciting new invention. If the 'quantum computer' can be made to work, we might be on the brink of a technological revolution.

For years, scientists have dreamt of quantum computers. By manipulating the quantum properties of atoms, at the very limits of scientific understanding, they hoped to build machines that would make the most powerful computers of today look like childish toys.

And now, that dream is closer to reality. Researchers at a conference in Texas have shown off a new device that points the way to a first working example of the technology. 'We're right at the bleeding edge,' said one scientist, 'of actually having a quantum processor.'

To understand why this quantum device matters, you have to understand a little about the history of computers themselves.

Today, a single silicon chip has more computer power than was held by all the allied nations combined at the end of the Second World War.

Your mobile phone is a more powerful computer than those which NASA used in the sixties to put men on the moon.

A Playstation 3, which costs about £200, is more powerful than a military supercomputer built as recently as 1997, at a cost of millions.

In fact, every 18 months, the memory you can squash onto a computer chip will more or less double. As computer chips get smaller, computers get more powerful. Complicated programmes can now be run on laptops, ipads, smartphones and even digital watches.

But there is a limit. Some time around 2020, predicts physicist Michio Kaku, we'll reach a point where connections in chips are only five atoms thick. Smaller than that, the laws of physics start to break down – and ordinary circuits stop working. That would mean computers would stop getting smaller, and the whole high-tech economy might grind disastrously to halt.

Quantum computers could solve that problem by working with the bizarre rules of quantum mechanics, the science that governs the behaviour of objects on an atomic scale. With quantum mechanics, you can make a tiny object called a 'qubit' that can be in two opposite states at the same time.

Quantum leap
By encoding information into qubits, you could revolutionise the way computers work. Their unique quantum properties mean that it might only take a few hundred qubits to outstrip the best computers we can produce today. In theory, they could give supercomputer levels of power crammed into a chip the size of a fingernail.

The possible uses are endless, from artificial intelligence to ultra-realistic gaming. We could do more science faster, and make impossible tasks easier. In fact, we may only be limited by our imaginations.

You Decide

  1. How much do you rely on computers in everyday life? Could you do without them?
  2. At the level of atoms and electrons, common-sense rules of physics start to break down. Things travel backwards in time; things can be in two places at once; information teleports across space. How weird is that?


  1. If you had a quantum supercomputer, what would you do with it? Write a science fiction story imagining what might happen.
  2. Do some research to find out what 'exponential growth' means. Why do some things grow exponentially and others not? Write a report on your findings – with examples of exponential and non-exponential growth.

Some People Say...

“Computers just make life complicated.”

What do you think?

Q & A

How can qubits be in two states at the same time?
Basically, in quantum mechanics, the normal rules of reality don't apply.
Why would being in two states at once make qubits useful for computers?
Because a computer could work with both states of a qubit at once. That means that for each qubit you add, the amount of information you can store grows exponentially.
Grows what?
Exponentially. Basically, the power doubles each qubit you add.
Doesn't sound like much.
Not with just a few qubits maybe. But try starting with 1 and doubling it 500 times. You'll get a number with 150 zeros – that's more than the number of atoms in the universe.
Impressive! Do many things grow that way?
Yes. Populations grow exponentially. Diseases – or viral videos – spread exponentially.