Quantum computing: Could your computer collapse into a black hole?

What are the fundamental limits of computing?

What are the fundamental limits of computing? How will quantum computers change information processing? And when might such machines be built and how?

Physicists and computer scientists are asking all these questions as they look to push the boundaries of information processing by seeking ways to harness quantum mechanics to accelerate computer hardware beyond the binary limits of the machines that sit on our desks today.

If they succeed in building a quantum computer, the disruption for our technology infrastructure will be vast - especially in terms of the online commerce we take for granted.

The advent of quantum computing could pose a threat to the security of ecommerce
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"Any time you order something from Amazon or from eBay or wherever, your web browser is encrypting your credit card number by a code, by some variant of the RSA code, which depends for its security on the belief that factoring enormous numbers is a much, much harder problem than multiplying them," Scott Aaronson, associate professor of electrical engineering and computer science at the Massachusetts Institute of Technology (MIT), told silicon.com.

"So far that belief has withstood 40 years of tests, but if we could build a quantum computer then that would no longer be true - then RSA would actually become insecure."

The challenge of building a quantum computer makes the business of packing billions of transistors onto a single chip look like child's play. When such a machine could exist outside a lab remains decades away at best, according to scientists in the field.

It may even prove impossible to build a quantum computer, say some.

Quantum computing research is at the very frontier of what's possible. However, even with so many practical technology hurdles ahead of it - what technologies to use and how to make them scale effectively - scientists are also asking what's next? Does anything come after quantum computers or are these machines really the final frontier for data processing?

Aaronson reckons computing could well hit a fundamental wall - and quantum gravity is to blame.

"It seems, from what we currently know about quantum gravity, that there's a fundamental limit to how fast you could ever run any computer," he says. "If you tried to run a computer faster than that then what would actually happen is that you would be using so much energy that you would exceed what's called the Schwarzschild value - and that means your computer would actually collapse to a black hole.

"It's that kind of thought experiment that makes it seem like a plausible conjecture that quantum computing is just the end of the line. It is an amazing thing that you can do - but maybe there's nothing more amazing than that."

For more on computing's quantum-fuelled future, read the full feature Quantum computing: Beyond computing's final frontier here.