Basic quantum computing circuit built

Feb 25, 2010 by Jill Sakai

(PhysOrg.com) -- Exerting delicate control over a pair of atoms within a mere seven-millionths-of-a-second window of opportunity, physicists at the University of Wisconsin-Madison created an atomic circuit that may help quantum computing become a reality.

Quantum computing represents a new paradigm in information processing that may complement classical computers. Much of the dizzying rate of increase in traditional computing power has come as transistors shrink and pack more tightly onto chips — a trend that cannot continue indefinitely.

"At some point in time you get to the limit where a single transistor that makes up an is one atom, and then you can no longer predict how the transistor will work with classical methods," explains UW-Madison physics professor Mark Saffman. "You have to use the physics that describes atoms — ."

At that point, he says, "you open up completely new possibilities for processing information. There are certain calculational problems... that can be solved exponentially faster on a quantum computer than on any foreseeable ."

With fellow physics professor Thad Walker, Saffman successfully used neutral atoms to create what is known as a controlled-NOT (CNOT) gate, a basic type of circuit that will be an essential element of any quantum computer. As described in the Jan. 8 issue of the journal , the work is the first demonstration of a between two uncharged atoms.

The use of neutral atoms rather than charged ions or other materials distinguishes the achievement from previous work. "The current gold standard in experimental has been set by trapped ions... People can run small programs now with up to eight ions in traps," says Saffman.

However, to be useful for computing applications, systems must contain enough , or qubits, to be capable of running long programs and handling more complex calculations. An ion-based system presents challenges for scaling up because ions are highly interactive with each other and their environment, making them difficult to control.

"Neutral atoms have the advantage that in their ground state they don't talk to each other, so you can put more of them in a small region without having them interact with each other and cause problems," Saffman says. "This is a step forward toward creating larger systems."

The team used a combination of lasers, extreme cold (a fraction of a degree above absolute zero), and a powerful vacuum to immobilize two rubidium atoms within "optical traps." They used another laser to excite the atoms to a high-energy state to create the CNOT quantum gate between the two atoms, also achieving a property called entanglement in which the states of the two atoms are linked such that measuring one provides information about the other.

Writing in the same journal issue, another team also entangled neutral atoms but without the CNOT gate. Creating the gate is advantageous because it allows more control over the states of the atoms, Saffman says, as well as demonstrating a fundamental aspect of an eventual quantum computer.

The Wisconsin group is now working toward arrays of up to 50 atoms to test the feasibility of scaling up their methods. They are also looking for ways to link qubits stored in atoms with qubits stored in light with an eye toward future communication applications, such as "quantum internets."

Explore further: Physicists design zero-friction quantum engine

Related Stories

Using degrees of freedom to get hyperentanglement

Jan 27, 2010

(PhysOrg.com) -- One of the biggest challenges scientists are grappling with today is the creation of an efficient quantum computer. There are a number of models out there, and hundreds of scientists and researchers around ...

Physicists Demonstrate Quantum Memory with Matter Qubits

Jul 03, 2009

(PhysOrg.com) -- For the first time, scientists have successfully operated a quantum gate between two remote particles of matter, marking an important step toward the development of a quantum computer. In ...

Analogue logic for quantum computing

Feb 21, 2008

Digital logic, or bits, is the only paradigm for the IT world, and up to now researchers used it almost exclusively to study quantum information processing. But European scientists, in a series of firsts, have proved that ...

Pushing quantum mechanics to higher levels

Aug 11, 2009

Scientists at UC Santa Barbara have devised a new type of superconducting circuit that behaves quantum mechanically -- but has up to five levels of energy instead of the usual two. The findings are published ...

Recommended for you

Physicists design zero-friction quantum engine

Sep 16, 2014

(Phys.org) —In real physical processes, some energy is always lost any time work is produced. The lost energy almost always occurs due to friction, especially in processes that involve mechanical motion. ...

Fluid mechanics suggests alternative to quantum orthodoxy

Sep 12, 2014

The central mystery of quantum mechanics is that small chunks of matter sometimes seem to behave like particles, sometimes like waves. For most of the past century, the prevailing explanation of this conundrum ...

The sound of an atom has been captured

Sep 11, 2014

Researchers at Chalmers University of Technology are first to show the use of sound to communicate with an artificial atom. They can thereby demonstrate phenomena from quantum physics with sound taking on ...

The quantum revolution is a step closer

Sep 11, 2014

A new way to run a quantum algorithm using much simpler methods than previously thought has been discovered by a team of researchers at the University of Bristol. These findings could dramatically bring ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Bloodoflamb
not rated yet Feb 25, 2010
UW - Madison represent! I was taught Introduction to Modern Physics by Thad, and had a number of friends who took Quantum from Saffman.
trucksmart
1 / 5 (1) Feb 26, 2010
I can't help but wonder if the future computers will use a different way of working with information.We now use 16 bits per character.I wish we could replace the binary system with one that would use some kind of short-hand system.In short-hand they use symbols to describe syllables.Normally syllables use two to five or more letters.With today's proof readers,utilizing short-hand a computer would require less memory and should be much quicker.
And there is the other possibility of copying the way DNA stores information and utilizes it.I realize this would cause a whole reworking of the computer language as we know it.But I think it would be worth it.With the advent of nano-tubes,we soon should be able to produce thinking materials and human-mechanical interfaces.