The Quantum Computing Game
BNC’s Prof. Jonathan Jones is fascinated by the strange puzzles of quantum computing
Interview by Olivia Gordon, Oxford Today
On a side table in Jonathan Jones’s college study stands an intriguing collection of pre-digital computers. They range from an abacus to a cylindrical slide-rule calculator to a 1960s cogs-and-gear calculating machine which works by turning a handle - it looks like an ancient relic. The University Lecturer in Atomic and Laser Physics reminisces about how when he was at school in the early 1980s, log tables were still commonplace. Now, he reflects, these devices are curiosities – but he keeps them on display as a reminder ‘that computation is mechanical; it’s not an abstract mathematical process. Information is physical; it has to be somewhere.’
Prof. Jones has been reading science fiction since the age of ten and his study shelves are half-filled with classics from Robert Heinlein to Ursula Le Guin. Having read chemistry at Oxford, he initially worked in biochemical and biomedical physics, but they weren’t for him – ‘in those fields you have to care about the problem itself – the disease or the molecule,’ he says. ‘But what I care about is not the problem, but how you solve it. Once I solve the problem, I’ve lost interest. In physics, we love the game. Nature is very simple if you look at it in the right way – you’re twisting things in your mind, trying to find the angle where everything becomes clear – and then, you’ve won!’
Quantum computing is the game Jones has been playing. Modern physics, based on quantum theory, which emerged at the turn of the 20th century, is ‘very strange,’ Prof. Jones explains, his eyes twinkling. ‘For instance, in the quantum world, things can be in many different states at once. And the thing about quantum objects is you mustn’t watch them – if you do, they suddenly stop being quantum objects and turn back into rather boring classical objects. So particles can be in two places at once - so long as you don’t look where they are.’
Prof. Jones has played an important role in developing quantum computing, which the next generation will start to use. His was the first group in the world to implement a quantum algorithm – an algorithm which can run on a quantum computer. Algorithms, he explains, are ways to solve a problem – a simple one is long multiplication. Computers work by using algorithms – and since the 1980s, physicists have been wondering what a computer built to run on quantum algorithms could do. In essence, such a computer would be able to explore many complex possibilities, and solve problems which currently elude modern computers.
In 1997, Prof. Jones and colleagues succeeded in building what he describes a ‘toy’ quantum computer, which simply proved it was possible. Instead of the ‘bits’ – the basic units of information - current computers use, these machines use quantum bits called qubits. The first machine had 2 qubits, and current machines have around 10. Engineers are now starting to build a prototype of a usable quantum computer. ‘In 10-20 years there will be working, real quantum computers,’ Prof. Jones says: ‘I’m now convinced.’ The immensely powerful calculating ability of such computers will transform our lives, from our understanding of the early universe to e-commerce (existing internet security, Jones says, ‘will be toast’).
Meanwhile, Prof. Jones has moved on to explore a ‘niche’ area. He’s trying to solve the problem of controlling the movement of a quantum particle without being able to watch it and correct any mistakes. ‘It would seem an impossible problem but it turns out there are rather complicated things you can do,’ he says. The tricks he is developing are called error-tolerant unitary transformations and he says they ‘will make building a quantum computer much, much easier’.
On Prof. Jones’ desk lies a textbook he co-wrote, Quantum Information, Computation and Communication. I flick to a page at random and read strange words: ‘Rabi flopping’; ‘Ramsey fringes’. What on earth is Rabi flopping, I ask. ‘It’s what happens when you apply light to an atom,’ Prof. Jones explains genially, demonstrating by rotating a ballpoint pen around in circles that an atom oscillates through ‘complicated intermediate states’. The term ‘Rabi’ is because this was discovered by Isidore Rabi, the father of nuclear magnetic resonance, he says – and ‘the flopping, I don’t really know!’ He tries valiantly to explain Ramsey fringes to me too – it’s how atomic clocks work - but I’m still mystified. ‘It’s sort of possible to explain it!,’ Prof. Jones laughs.
Jones, who lives in Oxford and has a student son, a mathematician, spends most of his time working on theoretical experiments on his computer, ‘coming up with and modeling ever more bizarre sequences of rotations’. His delight in the ‘madness’ of quantum theory is infectious: ‘In the quantum world, your instincts of what is true are unreliable. The world is not what you think it is. So let’s look for the maddest things we can find – that’s basically what physicists do! So far, it’s always worked.’