Quantum Leap - Researchers have controlled the position of a single electron in a silicon circuit.

An international team of researchers has shown that it can control the quantum state of a single electron in a silicon transistor--even putting the electron in two places at once. Their discovery could help pave the way toward a practical quantum computer.

Quantum computers take advantage of the strange properties of subatomic particles to perform certain types of calculations much faster than classical computers can. Researchers are exploring a host of different approaches to quantum computing, and some have even built primitive quantum circuits that can perform calculations. But practical quantum computing would require the ability to manufacture devices with millions of quantum circuits--rather than the 12 or 16 achievable now--that can be integrated with more-conventional electronics.

One theoretical approach to practical quantum electronics is to use conventional electronics--tiny semiconductor transistors--to control the state of a quantum system. Researchers led by Sven Rogge, a researcher at Delft University of Technology, in the Netherlands, performed the first practical experiments to verify the approach's theoretical predictions. The team--which also included researchers from Purdue University; the University of Melbourne, in Australia; and IMEC, in Belgium--found that it could control the quantum state of a single electron simply by altering the voltage applied to a transistor. "This represents a nice step towards future devices where performance is determined by manipulation of quantum states of single atoms," says Thomas Schenkel, a scientist at Lawrence Berkeley National Laboratory.

The researchers used prefabricated transistors built for nanotech research, each of which consisted of two crossed silicon nanowires. One of the nanowires--the bottom one--was connected to electrodes that contained arsenic. When that wire was charged, it would sometimes draw arsenic atoms into the transistor. After applying a voltage across about 100 transistors, the team found six that appeared to have individual arsenic atoms embedded in the nanowire. They then found that varying the voltage across the top wire would control the quantum state of one of the atom's electrons. Using an imaging technique called scanning tunneling spectroscopy, they were able to distinguish three states of the atoms in all six devices. One of those states corresponded with the electron's being in two places at the same time--a property necessary for quantum computing.

"But to understand the behavior of one atom, you have to model millions," says Rogge. So he and his colleagues used an off-the-shelf program called NEMO 3D to characterize a large-scale system containing 1.4 million atoms. They found that the measurements of their model system were in good agreement with the spectroscopy results. "It is really cool to see how well their simulations can describe randomly doped transistors, which are all different in detail," Schenkel says.

Depending on the strength of the electric field created by the top nanowire, an electron could be found in one of three states. At low electric fields, the electron remained bound to the arsenic atom. At high electric fields, the electron was pulled away from the atom. But when the electric field was at just the right level, the electron would be in both places at once.

In order for a quantum computer to work, its qubits--the quantum equivalent of a classical computer's bits--need to be "entangled": their quantum states have to be coupled with each other. Pulling an electron away from its atom "might be an interesting way to couple" adjacent qubits, says Schenkel.

"While this result is an important one, the real challenge to making future single-dopant devices is in figuring out how to position the [arsenic atoms] into the silicon host with the required precision," says Bruce Kane, a research scientist at the University of Maryland. The researchers found their six devices by chance; to produce working circuits, they would need to be able to position atoms of arsenic--or some other material--in the transistors more reliably.

While the researchers eventually hope to be able to control the position of the atoms in the transistor, "our next step is to add a second electron and see what happens to the configuration of the electron state," says Gabri Lansbergen, another Delft researcher. "In the far future," Rogge adds, "we would like to experiment with several [materials] and see how they interact."

The latest trend: 'microgreens'

By Jessica Vander Velde, Times Staff Writer

Published Monday, June 23, 2008 4:00 PM

---

ODESSA

Everything about Marvin Wilhite's farm is small — except the demand for his crop. His hydroponic operation uses less land and water than a traditional farm, but he pulls in $30 a pound for the microgreens he grows. You could imagine that as about 48 bags from the produce section of your supermarket.

The tiny, leafy vegetables, harvested before they reach an inch in height, are popular at high-end restaurants, including Cafe Ponte in Clearwater and Mise en Place in Tampa. They're tender and flavorful, and orders are on the rise as more chefs discover them and holistic doctors promote their nutritional value.

A delicate carpet of purple and green microgreens grows in a raised, shallow bed of sterilized white pebbles at Cahaba Club Herbal Outpost. The tables sit in a cooled greenhouse that protects fragile greens from rain and sun. A week after the seeds are sowed, the thin, tender stems measure about three-quarters of an inch: ready to harvest.

Wilhite grows 14 types of microgreens at his farm, including mustard, beets, broccoli and cabbage. Sampled fresh from the greenhouse, the micro mustard has a bit of a spicy kick like horseradish; the micro basil tastes more potent than its big brother. Chefs like the deep purples and greens — the "bling bling" on the plate, Wilhite said.

"It looks a lot prettier than parsley, and it tastes a lot better," he said.

But he didn't start growing microgreens for their look.

Researchers at Johns Hopkins University have found that broccoli shoots contain the cancer-fighting agent sulforaphane, more even than fully grown broccoli. So when his mother was diagnosed with ovarian cancer in 1999, he began to cultivate the greens. Her cancer went into remission for five years, and though it's impossible to directly link the greens to her improved health, he noted that she ate them every day.

Many of Wilhite's microgreens are sold to restaurants in the bay area and beyond — even Philadelphia and New York, he said. Of course, chefs are more concerned with how it looks on the plate than the phytochemicals.

But some doctors are becoming distributors, selling Wilhite's microgreens to patients. Bill Huggins, a researcher at the Nutritional Health Institute Laboratories in Clearwater, suggests that people battling chronic illnesses try microgreens.

"It's basically the best kind of nutrition you can get from the plant kingdom," he said.

As the vegetables grow in popularity, farmers are taking notice. Each year, small-farm operators gather in North Florida to learn new techniques. This year extension agent Robert Hochmuth of Live Oak gave tips on how to start growing microgreens, another option for small farmers looking to diversify their crop.

"The diversity is important so they don't have all their eggs in one basket," he said.

Of course, now that everyone's using microgreens, top chefs are looking for the next trend: a slightly larger version. These "tiny exotic vegetables" — about 1.5 inches tall — taste a lot like microgreens but they look different because they've reached the second leaf stage. The micro mustard's tiny leaves begin to look like gloves, Wilhite said.

Chris Ponte, chef-owner of Cafe Ponte, said he's interested in these tiny vegetables, which are smaller than the types of baby vegetables often found in salads.

"Once the mainstream gets the product, it takes away from the wow factor for the guests," he said.

Wilhite keeps in touch with chefs, and he recently started a greenhouse devoted to tiny vegetables.

"It's something people haven't seen before," he said.

Jessica Vander Velde can be reached at jvandervelde@sptimes.com or (813) 661-2443.

>>fast facts

Shopping for microgreens?

To buy Cahaba Club's:

Cahaba Club Herbal Outpost in Odessa sells a set of six 1.5-ounce packs to the public for $25. It includes two packages of micro red cabbage, two of micro red kale and two of micro broccoli. Shipping and handling is extra, or buyers can pick them up at Cahaba Club Herbal Outpost at 18625 Rustic Woods Trail, Odessa. To place an order, call Pat Whitehead at (727) 937-8076 or fax him at (727) 937-8408.

To grow your own
microgreens

A husband-wife team in California sells microgreen kits and seeds online at sproutpeople.com.