Published by Australian Academy of Science
Quantum computers – why would you want one? Box 3 | So when will we have one?

We are in fact a long way from everyday quantum computers or even practical ones, though quite a few laboratories are grappling with the challenges. No one has so far assembled more than a dozen or so qubits, well short of the numbers needed to solve important problems. Experimental quantum computers have done some not very difficult sums, so they do work. One has reportedly managed to solve a Sudoku, though that will not impress people who do it every day.

But before you can get your hands on a quantum computer, there are still a lot of practical questions to be solved.

How can we stop the qubits from being accidentally bumped and so spilling out an answer before the calculation is complete?
Information stored in qubits can be protected from any data handling errors by employing quantum error correction schemes. These schemes have been demonstrated in quantum computing systems consisting of up to 8 qubits.

What is the best way to interact with the qubits, to feed information in and get answers out?
Pulses of radio waves, like those in a magnetic resonance imaging (MRI) machine are working promisingly there, though the interchange is still quite slow.

How many qubits will we actually be able to assemble and work together?
As few as 300 qubits would be sufficient to outperform computational simulations of physical and chemical systems currently achieved with conventional computers. However, millions of qubits are required to provide a public key encryption system that is superior to the current one.

Related sites

• First 'commercial' quantum computer solves sudoku puzzle (Scientific American, 13 February 2007)

• NIST demonstrates data 'repair kit' for quantum computers (National Institute of Standards and Technology, USA)

• Stable quantum mechanical memory and a small quantum processor created (What's Next in Science and Technology, USA)

• A quantum leap in computing (MSNBC.com, USA)

• New hurdle for quantum computing (Science A Go Go, Australia)

Box 1. Into the nanoworld

Box 2. What are we up to here in Australia?