Feeds

Noise can improve quantum computing, says ANU scientist

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

Security for virtualized datacentres

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. ®

Security for virtualized datacentres

More from The Register

next story
Boffins say they've got Lithium batteries the wrong way around
Surprises at the nano-scale mean our ideas about how they charge could be all wrong
Thought that last dinosaur was BIG? This one's bloody ENORMOUS
Weighed several adult elephants, contend boffins
Europe prepares to INVADE comet: Rosetta landing site chosen
No word yet on whether backup site is labelled 'K'
City hidden beneath England's Stonehenge had HUMAN ABATTOIR. And a pub
Boozed-up ancients drank beer before tearing corpses apart
'Duck face' selfie in SPAAAACE: Rosetta's snap with bird comet
Probe prepares to make first landing on fast-moving rock
Archaeologists and robots on hunt for more Antikythera pieces
How much of the world's oldest computer can they find?
LOHAN invites ENTIRE REG READERSHIP to New Mexico shindig
Well, those of you who back our Kickstarter tin-rattling...
prev story

Whitepapers

Secure remote control for conventional and virtual desktops
Balancing user privacy and privileged access, in accordance with compliance frameworks and legislation. Evaluating any potential remote control choice.
Saudi Petroleum chooses Tegile storage solution
A storage solution that addresses company growth and performance for business-critical applications of caseware archive and search along with other key operational systems.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.
Providing a secure and efficient Helpdesk
A single remote control platform for user support is be key to providing an efficient helpdesk. Retain full control over the way in which screen and keystroke data is transmitted.