Single-atom writer a landmark for quantum computing
September 19, 2012

This is an artist&#8217;s impression of a phosphorus atom (red sphere surrounded by electron cloud, with arrow showing the spin direction) coupled to a silicon single-electron transistor. A burst of microwaves (blue) is used to &#8216;write&#8217; information on the electron spin. Credit: Tony Melov

A research team led by Australian engineers has created the first working quantum bit based on a single atom in silicon, opening the way to ultra-powerful quantum computers of the future.

In a landmark paper published today in the journal Nature, the team describes how it was able to both read and write information using the spin, or magnetic orientation, of an electron bound to a single phosphorus atom embedded in a silicon chip.

"For the first time, we have demonstrated the ability to represent and manipulate data on the spin to form a quantum bit, or 'qubit', the basic unit of data for a quantum computer," says Scientia Professor Andrew Dzurak. "This really is the key advance towards realising a silicon quantum computer based on single atoms."

Dr Andrea Morello and Professor Dzurak from the UNSW School of Electrical Engineering and Telecommunications lead the team. It includes researchers from the University of Melbourne and University College, London.

"This is a remarkable scientific achievement &#8211; governing nature at its most fundamental level &#8211; and has profound implications for quantum computing," says Dzurak.

Dr Morello says that quantum computers promise to solve complex problems that are currently impossible on even the world's largest supercomputers: "These include data-intensive problems, such as cracking modern encryption codes, searching databases, and modelling biological molecules and drugs."

The new finding follows on from a 2010 study also published in Nature, in which the same UNSW group demonstrated the ability to read the state of an electron's spin. Discovering how to write the spin state now completes the two-stage process required to operate a quantum bit.

Granny says if possum keeps givin' her the razzberry - dey gonna get inna entanglement...Scientists achieve reliable quantum teleportation for first timeMay 29, 2014 ~ Einstein is wrong? That's the potential outcome of a quantum mechanics study as scientists race to disprove his views on entanglement.

Albert Einstein once told a friend that quantum mechanics doesn't hold water in his scientific world view because "physics should represent a reality in time and space, free from spooky actions at a distance." That spooky action at a distance is entanglement, a quantum phenomenon in which two particles, separated by any amount of distance, can instantaneously affect one another as if part of a unified system. Now, scientists have successfully hijacked that quantum weirdness -- doing so reliably for the first time -- to produce what many sci-fi fans have long dreamt up: teleportation. No, not beaming humans aboard the USS Enterprise, but the teleportation of data.

Physicists at the Kavli Institute of Nanoscience, part of the Delft University of Technology in the Netherlands, report that they sent quantum data concerning the spin state of an electron to another electron about 10 feet away. Quantum teleportation has been recorded in the past, but the results in this study have an unprecedented replication rate of 100 percent at the current distance, the team said. Thanks to the strange properties of entanglement, this allows for that data -- only quantum data, not classical information like messages or even simple bits -- to be teleported seemingly faster than the speed of light. The news was reported first by The New York Times on Thursday, following the publication of a paper in the journal Science.

Proving Einstein wrong about the purview and completeness of quantum mechanics is not just an academic boasting contest. Proving the existence of entanglement and teleportation -- and getting experiments to work efficiently, in larger systems and at greater distances -- holds the key to translating quantum mechanics to practical applications, like quantum computing. For instance, quantum computers could utilize that speed to unlock a whole new generation of unprecedented computing power. Quantum teleportation is not teleportation in the sense one might think. It involves achieving a certain set of parameters that then allow properties of one quantum system to get tangled up with another so that observations are reflected simultaneously, thereby "teleporting" the information from one place to another.

To do this, researchers at Delft first had to create qubits out of classical bits, in this case electrons trapped in diamonds at extremely low temperatures that allow their quantum properties, like spin, to be observed. A qubit is a unit of quantum data that can hold multiple values simultaneously thanks to an equally integral quantum phenomenon called superposition, a term fans of the field will accurately associate with the Schrödinger equation, as well as Heisenberg's uncertainty principle that says something exists in all possible states until it is observed. It's the same way quantum computing may one day surpass the speeds of classical computing by allowing calculations to spread bit values between 0, 1 or any probabilistic value between the two numbers -- in other words, a superposition of both figures.

With quibits separated by a distance of three meters, the researchers were able to observe and record the spin of one electron and see that reflected in the other qubit instantly. It's an admittedly wonky conception of data teleportation that requires a little head scratching before it begins to clear up. Still, its effects could be far reaching. The researchers are attempting to increase that distance to more than a kilometer, which would be ample leeway to test whether or not entanglement was a consistent phenomenon and that the information was traveling faster than the speed of light. Such experiments would more definitively knock down Einstein's disqualification of entanglement due to its violation of classical mechanics. "There is a big race going on between five or six groups to prove Einstein wrong," Ronald Hanson, a physicist leading the research at Delft, told The New York Times. "There is one very big fish."

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