Quantum computer built inside a diamond

Apr 04, 2012

Diamonds are forever – or, at least, the effects of this diamond on quantum computing may be. A team that includes scientists from USC has built a quantum computer in a diamond, the first of its kind to include protection against "decoherence" – noise that prevents the computer from functioning properly.

The demonstration shows the viability of solid-state quantum computers, which – unlike earlier gas- and liquid-state systems – may represent the future of quantum computing because they can be easily scaled up in size. Current quantum computers are typically very small and – though impressive – cannot yet compete with the speed of larger, traditional computers.

The multinational team included USC Professor Daniel Lidar and USC postdoctoral researcher Zhihui Wang, as well as researchers from the Delft University of Technology in the Netherlands, Iowa State University and the University of California, Santa Barbara. Their findings will be published on April 5 in Nature.

The team's diamond quantum computer system featured two quantum bits (called "qubits"), made of subatomic particles.

As opposed to traditional computer bits, which can encode distinctly either a one or a zero, qubits can encode a one and a zero at the same time. This property, called superposition, along with the ability of quantum states to "tunnel" through energy barriers, will some day allow quantum computers to perform optimization calculations much faster than traditional computers.

Like all , the diamond used by the researchers has impurities – things other than carbon. The more impurities in a diamond, the less attractive it is as a piece of jewelry, because it makes the crystal appear cloudy.

The team, however, utilized the impurities themselves.

A rogue nitrogen nucleus became the first qubit. In a second flaw sat an electron, which became the second qubit. (Though put more accurately, the "spin" of each of these subatomic particles was used as the qubit.)

Electrons are smaller than nuclei and perform computations much more quickly, but also fall victim more quickly to "decoherence." A qubit based on a nucleus, which is large, is much more stable but slower.

"A nucleus has a long decoherence time – in the milliseconds. You can think of it as very sluggish," said Lidar, who holds a joint appointment with the USC Viterbi School of Engineering and the USC Dornsife College of Letters, Arts and Sciences.

Though solid-state computing systems have existed before, this was the first to incorporate decoherence protection – using microwave pulses to continually switch the direction of the electron spin rotation.

"It's a little like time travel," Lidar said, because switching the direction of rotation time-reverses the inconsistencies in motion as the qubits move back to their original position.

The team was able to demonstrate that their diamond-encased system does indeed operate in a quantum fashion by seeing how closely it matched "Grover's algorithm."

The algorithm is not new – Lov Grover of Bell Labs invented it in 1996 – but it shows the promise of .

The test is a search of an unsorted database, akin to being told to search for a name in a phone book when you've only been given the phone number.

Sometimes you'd miraculously find it on the first try, other times you might have to search through the entire book to find it. If you did the search countless times, on average, you'd find the name you were looking for after searching through half of the phone book.

Mathematically, this can be expressed by saying you'd find the correct choice in X/2 tries – if X is the number of total choices you have to search through. So, with four choices total, you'll find the correct one after two tries on average.

A quantum computer, using the properties of superposition, can find the correct choice much more quickly. The mathematics behind it are complicated, but in practical terms, a quantum computer searching through an unsorted list of four choices will find the correct choice on the first try, every time.

Though not perfect, the new computer picked the correct choice on the first try about 95 percent of the time – enough to demonstrate that it operates in a quantum fashion.

Explore further: Interview with Gerhard Rempe about the fascination of and prospects for quantum information technology

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User comments : 8

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3 / 5 (2) Apr 04, 2012
Diamonds are exceptional by strength of chemical bonds and the stability of excited states of nitrogen vacancies. It manifests with reddish fluorescence of natural diamond specimens, which lasts for seconds. The high energetic barrier of chemical bonds prohibits their spontaneous decoherence with thermal vibrations. These vacancies can be observed as glowing spots under the microscope, which is exceptional if we realize, they're represented with single atom domains. Only cooled atoms within Bose-Einstein's condensate are behaving in similar way, which means, the diamond enables to replicate some expensive experiments made with fragile boson condensates at room temperature comfortably.
1 / 5 (6) Apr 04, 2012
Neat trick but when can we play World of Warcraft on them?
3.7 / 5 (3) Apr 05, 2012
Neat trick but when can we play World of Warcraft on them?

Crysis dude....Crysis....
not rated yet Apr 05, 2012
The first country to get a working quantum computer might be able to crack all codes in existence. It's like getting the nuclear weapon first, race to build a quantum computer == the Manhattan project? Will it be like this?
not rated yet Apr 05, 2012
@Feldagast and thematrix606: Quantum computers will not help your triangles. ;) But they could lead to much more accurate physics at a similar load to current methods.

@Blakut: You could break a hash where you know the equation, but if you don't know the equation used to encrypt, the data is still garbage. A threat to standardized encryption mothods, but not to anything custom.
2 / 5 (2) Apr 05, 2012
@Feldagast and thematrix606: Quantum computers will not help your triangles. ;) But they could lead to much more accurate physics at a similar load to current methods.

Actually, quantum algorithms could help in some cases for video games in certain scripting or random number situations.

There are situations in games where you need a random number to make a random event happen, or do roll dice for a truly random number.

Conventional computers handle this by iteration of a ridiculously complicated random number formula, and, for example, a "dice" system.

If your character has 5D6 in a skill or attribute, etc, then it ends up calling the function 5 times and tallying the results, etc.

IN some situations, a quantum computer may be able to handle randomization in far fewer steps, which is a huge, huge thing in many video games.
not rated yet Apr 11, 2012
"You could break a hash where you know the equation... A threat to standardized encryption mothods, but not to anything custom"

There's a reason why security in modern encryption relies on the key being kept secret, not the algorithm. It's because algorithms are notoriously weak, and your best bet is to spread it far and wide and let the best cryptographic minds figure out if there's holes or not.

If data is encrypted using anything other than a one time pad, it's vulnerable. The vast (VAST) majority of that data would be vulnerable to attacks using improved methods of factoring primes, and that includes any "custom" encryption.

Quantum computers have the potential to crack any data encrypted with an algorithm that relies on the difficulty of factoring primes in a single pass. Most data out there relies on this difficulty for the simple reason that any other custom algorithms are pretty weak by comparison, and *still* might be child's play to a quantum computer.

1 / 5 (1) Apr 11, 2012
@Feldagast and thematrix606: Quantum computers will not help your triangles. ;) But they could lead to much more accurate physics at a similar load to current methods.

@Blakut: You could break a hash where you know the equation, but if you don't know the equation used to encrypt, the data is still garbage. A threat to standardized encryption mothods, but not to anything custom.

As Lurker so thoughtfully pointed out, just random number generation alone would be a huge step forward. Also, many rendering processes use filtering techniques and pixel-comparisons that would benefit greatly from quantum GPUs (e.g. single-step pixel supersampling).

As for the encryption problem, you see, the thing is that mathematical and program equations and formulas are also information in and of themselves. You can already "search" for a formula using specialized software. It increases complexity exponentially and adds more parameters, but true quantum processing makes those points moot

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