Listening to electrons: New method brings scaling-up quantum devices one step closer

February 1, 2013
PhD students James Colless and Alice Mahoney preparing a dilution refrigerator for experiments on quantum dots. Temperatures close to absolute zero are required to study the quantum behaviour.

(—We're now one step closer to quantum computing becoming a reality thanks to research led by a team of University of Sydney physicists, who have found a new way to detect changes in charges smaller than one electron.

The research is published in this week's edition of .

"Our new method for detecting charge in is exciting and has implications for a range of nanotechnologies," said Associate Professor David Reilly, from the ARC Centre for Engineered Quantum Systems in the School of Physics at the University of Sydney.

"We've been successful in finding a new, more convenient way to detect changes in charge of a single electron on quantum dots. Quantum dots are that can confine or trap single electrons," explained Associate Professor Reilly.

"Electrons confined to quantum dots are very nice systems for storing and manipulating quantum information, where data is encoded in the quantum mechanical aspects of the electron. Our goal is to scale-up a large number of quantum dots to ultimately create a machine to process quantum information - a quantum computer."

Ever since highlighted the potential of quantum computing in the 1980s, scientists have been attempting to build quantum computers capable of solving some of the largest and most complex problems, with much greater efficiency than conventional computers.

"We've focused on quantum dots as their properties can be tuned in the laboratory - we can control their by turning a knob in the lab."

"Being able to detect single electron charges on the quantum dots is absolutely essential, as it's the way information is retrieved from such quantum . We call it 'read-out' and it's analogous to reading information from the memory or a hard drive in a regular ," said Associate Professor Reilly.

"Without the ability to read-out , we have no way of getting the answer to a computation!"

The team, including School of Physics PhD students James Colless, Alice Mahoney and John Hornibrook, and Associate Professor Andrew Doherty and Associate Professor David Reilly, with two scientists from the University of California, Santa Barbara, have found a new way of detecting charge on the quantum dots using the gate electrodes already in the system.

"Previously, sensitive electrometers which measure minute charges were used to read-out the electron state on . These work well, but they are somewhat separate devices built onto the ends of the quantum dot system. They are a bit like having microphones nearby that can pick up the sound of electrons," explained Associate Professor Reilly.

"What we have shown is that the gates or electrodes that are already in place to create the quantum dot in the first place, can also act as read-out detectors. This means you don't need separate devices and you don't need to worry about how to place those separate electrometer devices."

"Whereas the old system was like having microphones nearby to detect sound, our new system could be likened to using the walls of a room as in-built microphones - you don't need separate microphones for every room of the house, just use the walls as microphones," said Associate Professor Reilly.

"Our new method makes the whole quantum system easier to build and use, as adding nanoscale electrometers for every quantum dot in a million-dot-array is a hard problem. By using the electrodes already in the system, we've found an efficient new way to measure charge in the big quantum systems of the future."

The new method of detection allows for read-out in large dot arrays with no limitation on the size of the array for the read-out method to work.

James Colless, whose PhD research contributed greatly to the finding, said, "The technologies that we are developing are part of a global research effort to advance the prospect of . In a similar way to how billions of transistors can now be placed on a single silicon computer chip, in the future we would like to engineer semiconductor chips containing huge numbers of interacting quantum two-level systems - called qubits. The work presented in this paper suggests a new method of reading out qubits that enables this goal."

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3 / 5 (4) Feb 01, 2013
Month ago - "one step closer". Today - "one step closer". I don't care if quantom or graphene computing is one step closer if it's a million steps away. When will i be able to buy a quantum/graphene processor on
2 / 5 (4) Feb 01, 2013
Same old mantra.
1 / 5 (1) Feb 01, 2013
If a useful quantum computer is built some day in the future, you can bet your ass that it'll be first used to crack some very tough scientific problems that are practically impossible on "classical" computers. If you want a new fancy toy, you'll most likely have to wait quite a while.
2.3 / 5 (6) Feb 01, 2013
When will i be able to buy a quantum/graphene processor on

If you're not satisfied with the speed of development then go and do some research and make it go faster. What's that you're saying? You have no clue about quantum physics or what a quantum computer does?

Then stop harping on the people who are actually doing something. Because if it were up to people like you we could wait a million years and wouldn't ever be one step closer.

Armchair coaches. Pathetic.
1 / 5 (4) Feb 01, 2013
Conservatives become very annoyed by any problem that can't be solved immediately by throwing money at it: A clear symptom of brain damage
3.3 / 5 (6) Feb 01, 2013
Conservatives become very annoyed by any problem that can't be solved immediately by throwing money at it: A clear symptom of brain damage

And liberals become very annoyed when they aren't allowed to keep throwing money at the same idea that didn't solve the problem: A clear symptom of insanity.

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