Feeds

Noise can improve quantum computing, says ANU scientist

It’s quantum computing: of course there’s a paradox

Secure remote control for conventional and virtual desktops

Here’s a nice paradox: since noise gets in the way of quantum computing, cure it by adding more noise.

That startling proposal is the work of a team led by the Australian National University’s Dr André Carvalho, along with collaborators from Brazil and Spain.

Noise is normally treated as the enemy in quantum-level experiments, because it destroys the useful characteristics of qubits (quantum computing elements). As Dr Carvalho explained to The Register, “in the quantum world, these operations work because the qubits can be in a state of superposition” (that is, multiple possible states existing at the same time – as did the famous cat belonging to Herr Schrödinger').

“Those coherence properties disappear with time, and that means the main resource, entanglement, disappears with noise.”

The particular kind of noise Carvalho’s work deals with is the spontaneous emission of photons. This means, simply, that if a qubit starts in a “1” state, it will eventually emit a photon and fall to a “0” state.

Without a solution to the noise problem, Dr Carvalho says, computation becomes impossible. “Because we have no control on the outcomes of the measurement – they are totally random – if we just passively wait it would take an infinite amount of time to extract even a very simple computation.”

Dr Carvalho’s solution is two-fold: first, to add noise (as photons, using a laser) back into a qubit before the state-decay takes place; second, to perform measurement on the system in just the right way.

If, after adding the extra noise, the system were simply left alone, decoherence will happen more quickly, he said. “But if we measure the photons that are coming out, and measure them in the right way, then at the end of the measurement, we have a quantum gate.”

In other words, under the right circumstances, the act of measurement is what creates the quantum gate that can perform computation.

Unfortunately, measurement, like noise, is an enemy of entanglement and superposition. Just as in Schroedinger’s thought experiment, if you “look in the box”, the quantum system will resolve itself into a classical state.

“When you measure a quantum system, you destroy the system,” he said. “If you measure the state of a photon, you will know that it’s in a particular state.”

However, because of the added noise, he said, there are two kinds of photons available for measurement – those that are created by spontaneous emission, and those added in the excitation process.

“We have two kinds of photons, the spontaneous and the ‘noisy channel’,” he said – and since the detector “can’t tell whether the photon is coming from one process or the other, that creates a superposition.”

If you want a more metaphorical description of the process, the ANU puts it like the “million monkeys typing Shakespeare” problem: it becomes much more likely if you capture keystrokes that appear in the correct order.

Dr Carvalho's work has been published in Physical Review Letters. ®

Next gen security for virtualised datacentres

More from The Register

next story
Gigantic toothless 'DRAGONS' dominated Earth's early skies
Gummy pterosaurs outlived toothy competitors
Vulture 2 takes a battering in 100km/h test run
Still in one piece, but we're going to need MORE POWER
TRIANGULAR orbits will help Rosetta to get up close with Comet 67P
Probe will be just 10km from Space Duck in October
Boffins ID freakish spine-smothered prehistoric critter: The CLAW gave it away
Bizarre-looking creature actually related to velvet worms
CRR-CRRRK, beep, beep: Mars space truck backs out of slippery sand trap
Curiosity finds new drilling target after course correction
'Leccy racer whacks petrols in Oz race
ELMOFO rakes in two wins in sanctioned race
Astronomers scramble for obs on new comet
Amateur gets fifth confirmed discovery
What does a flashmob of 1,024 robots look like? Just like this
Sorry, Harvard, did you say kilobots or KILLER BOTS?
NASA's rock'n'roll shock: ROLLING STONE FOUND ON MARS
No sign of Ziggy Stardust and his band
prev story

Whitepapers

5 things you didn’t know about cloud backup
IT departments are embracing cloud backup, but there’s a lot you need to know before choosing a service provider. Learn all the critical things you need to know.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.
Rethinking backup and recovery in the modern data center
Combining intelligence, operational analytics, and automation to enable efficient, data-driven IT organizations using the HP ABR approach.
Next gen security for virtualised datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.