Scientists Make Water Run Uphill

Watch the drop move Physicists have made water run uphill quite literally under its own steam.

The droplets propel themselves over metal sheets scored with a carefully designed array of grooves.

The US scientists did the experiment to demonstrate how the random motion of water molecules in hot steam could be channelled into a directed force.

But the team, writing in Physical Review Letters, believes the effect may be useful in driving coolants through overheating computer microchips.

Leave an empty pan on the stove for too long, and water, when you drip it over the scorching pan bottom, will hover over the surface on a bed of steam.

The effect was described in the 18th Century by a German scientist Johann Gottlob Leidenfrost.

What happens is that the heat is so intense, it boils the underside of the water droplet without any physical contact with the pan.

"We were interested in whether it would be possible to use this phenomenon to move liquids around," said Dr Heiner Linke, the intellectual power behind the self-propelled droplets.

The trick seems simple. Instead of using a smooth surface, the team scored it with a series of skewed triangular grooves. This gives it a kind of saw-tooth profile.

Now the water droplets appear to push themselves off the long-slope side of the grooves and rocket across the heated surface - instead of just dancing on the spot as they do in the kitchen pan.

The mechanism is a little more complicated and took a while to work out, Dr Linke told the BBC. "The vapour," he explained, "mostly flows in one direction, and the droplet sits on the flowing vapour, a bit like a boat carried along in a flowing river."

Droplets can also climb over steps, and up inclines of up to 12 degrees. Filmed with high-speed cameras, the droplets appear to take on a life of their own, sliding along like sloppy amoebae.

Although the original intention was to devise an arresting demonstration of how random energy can be rectified into directed motion - the focus of Dr Linke's main work is with molecular motors - the researchers now think there may be a use for the effect in cooling computer microchips.

The electrical currents now passing through microprocessors are so large the heat they generate can limit computing performance.

Many chips have cooling circuits nowadays, but these require pumps to drive the coolant, which in turn generate even more heat.

Suitably micro-patterned channels, argues Dr Linke, would make the coolant flow automatically.

"It would be very neat if we could use the heat from the chip to be the pump, because you would not need any additional power, but also because the pumping only happens when the thing is warm; it would also be a thermostat at the same time. So it would all be in one package."

You think thats weird, look at what my quantum mechanics professor recently did. A computer that runs when its off, well sorta, its on and off a the same time.

CHAMPAIGN, Ill. — By combining quantum computation and quantum interrogation, scientists at the University of Illinois at Urbana-Champaign have found an exotic way of determining an answer to an algorithm – without ever running the algorithm.

Using an optical-based quantum computer, a research team led by physicist Paul Kwiat has presented the first demonstration of “counterfactual computation,” inferring information about an answer, even though the computer did not run. The researchers report their work in the Feb. 23 issue of the journal Nature.

Quantum computers have the potential for solving certain types of problems much faster than classical computers. Speed and efficiency are gained because quantum bits can be placed in superpositions of one and zero, as opposed to classical bits, which are either one or zero. Moreover, the logic behind the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to some surprising effects.

“It seems absolutely bizarre that counterfactual computation – using information that is counter to what must have actually happened – could find an answer without running the entire quantum computer,” said Kwiat, a John Bardeen Professor of Electrical and Computer Engineering and Physics at Illinois. ”But the nature of quantum interrogation makes this amazing feat possible.”

Sometimes called interaction-free measurement, quantum interrogation is a technique that makes use of wave-particle duality (in this case, of photons) to search a region of space without actually entering that region of space.

Utilizing two coupled optical interferometers, nested within a third, Kwiat’s team succeeded in counterfactually searching a four-element database using Grover’s quantum search algorithm.

“By placing our photon in a quantum superposition of running and not running the search algorithm, we obtained information about the answer even when the photon did not run the search algorithm,” said graduate student Onur Hosten, lead author of the Nature paper. “We also showed theoretically how to obtain the answer without ever running the algorithm, by using a ‘chained Zeno’ effect.”

Through clever use of beam splitters and both constructive and destructive interference, the researchers can put each photon in a superposition of taking two paths. Although a photon can occupy multiple places simultaneously, it can only make an actual appearance at one location. Its presence defines its path, and that can, in a very strange way, negate the need for the search algorithm to run.

“In a sense, it is the possibility that the algorithm could run which prevents the algorithm from running,” Kwiat said. “That is at the heart of quantum interrogation schemes, and to my mind, quantum mechanics doesn’t get any more mysterious than this.”

While the researchers’ optical quantum computer cannot be scaled up, using these kinds of interrogation techniques may make it possible to reduce errors in quantum computing, Kwiat said. “Anything you can do to reduce the errors will make it more likely that eventually you’ll get a large-scale quantum computer.”

In addition to Kwiat and Hosten, co-authors of the Nature paper are graduate students Julio Barreiro, Nicholas Peters and Matthew Rakher (now at the University of California at Santa Barbara). The work was funded by the Disruptive Technologies Office and the National Science Foundation.

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