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Tales from the quantum frontier


  Click for interactive: Learn more about quantum mechanics and its application to computing.

The quantum world may seem so small and weird that there's no connection with everyday reality, but that impression couldn't be further from the truth. Newly published studies - and a newly released documentary - explore the big frontiers of the quantum information revolution.

Actually, quantum physics is as connected to everyday reality as the device that's displaying these words of mine. If it weren't for the quantum nature of light, inventions such as computers, TVs and DVD players would be impossible.

Some aspects of quantum mechanics are easier to understand than others, however. It's one thing to wrap your mind around the idea that light comes in individual packets called photons, and quite another to suggest that a single photon can travel along two paths at once. Or to suggest that two photons can be linked so strongly that doing something to one of them affects the other. Even Albert Einstein said that was "spooky."

It may be that our brains just aren't programmed to pick up on the weirder implications of quantum physics, such as superposition, information teleportation and particle entanglement. But Anton Zeilinger, a University of Vienna physicist who pioneered the technology behind teleportation, says that doesn't always have to be the case.

"I'm dreaming of teaching small children, maybe 4-year-olds, about quantum phenomena," he told me this week. "You can't teach them the math, that's quite clear. But you can show them apparatuses or simulate this behavior in a quantum way, just to see what they make out of it. Maybe if you get exposed early, you have a better intuitive grasp."

With repeated exposure, students get the idea that quantum information isn't that spooky after all, said Ray Laflamme, director of the Institute for Quantum Computing at the University of Waterloo in Ontario. He compared the current age to the 19th century, when the famed physicist Lord Kelvin declared that "heavier-than-air flying machines are impossible."

"We don't have the technology ... to build the intuition," Laflamme told me. He said it would be up to the next generation to absorb quantum concepts "so that it becomes second nature - just as when you get on a plane, you don't think, 'Is this thing really going to fly?'"

Quantum devices: Ready for takeoff?
One of the concepts that's just beginning to take off is the idea that it should be possible to extend the quantum world from the realm of the super-small  to a scale large enough to allow for the construction of actual devices for information processing.

A paper published in Thursday's issue of Nature takes a big leap in that direction by describing the creation of a quantum information device big enough to be seen with the naked eye. The device, which looks like a computer chip, links together a superconducting quantum-bit circuit with a tiny mechanical resonator capable of vibrating nearly 6 billion times a second.

The device was chilled down to a temperature of 25 millikelvin, or roughly 0.05 degrees Fahrenheit above absolute zero. Andrew Cleland, a physicist at the University of California at Santa Barbara who was on the research team, explained that the chip had to get that cold to cut down on the noise of vibrating atoms. "Everything on your desk is vibrating ever so slightly because it's at a non-zero temperature," he told me.


O'Connell et al. / Nature
  This optical micrograph shows a mechanical resonator connected to a quantum-bit circuit on a chip. The resonator, at the bottom of the chip, is about 60 microns wide, or about the width of a human hair.

Twenty-five millikelvin is pretty cold - colder than the chilliest corners of outer space, in fact - but if the resonator weren't vibrating so rapidly, it'd have to get even colder. A typical tuning fork, for example, would have to be chilled down to less than a millionth of a degree above absolute zero to exhibit quantum properties.

The quantum-bit circuit could be used to measure the quantum state of the resonator, or create a single excitation in the resonator. The results demonstrated that a device containing trillions of atoms could do the same quantum tricks usually seen only on the scale of dozens of atoms.

"We were just trying to demonstrate quantum effects in a big thing," Cleland said. "But a possible application would be if you try to detect these acoustic vibrations at the quantum level. You could do it with this. You could use it as a quantum microphone, or a quantum loudspeaker."

In a commentary also published by Nature, University of Vienna physicist Markus Aspelmeyer said Cleland and his colleagues "have taken a decisive first step towards an exciting future in mechanical quantum physics." Resonators like the one described in the Nature paper could conceivably be used as sensors for quantum effects, or memory devices for quantum computers, or interfaces to read out the results of a quantum calculation.

Yet another paper in Nature describes the combination of super-cooled gas and a single trapped ion to create a different type of hybrid quantum system that could find its way into future computing systems.

The federal government has long been interested in quantum computing: The Pentagon's Defense Advanced Research Projects Agency has a multimillion-dollar program for quantum entanglement science and technology, and the National Science Foundation recently awarded a $900,000 grant to support the development of quantum computer hardware.

Reality check for quantum computers
I wrote my first story about the promise of quantum computing almost 10 years ago - and at the time, some physicists were saying that a computer capable of manipulating 30 bits of quantum information, or qubits, just might be developed by ... um, 2010.

Back in the real world, researchers proudly announced last year that they had created a two-qubit chip, and Laflamme said today's experiments can deal with only 10 qubits or so. "You wouldn't go very far on the stock market if you had just 10 quantum bits, but for the science and technology of quantum information, it's critical," he said.

A couple of years ago, Canada's D-Wave Systems claimed that it successfully incorporated quantum-mechanical principles in one of its computer models, but backed away from suggestions that it had built a general-purpose quantum computer.

"Maybe a few people might have been foolish enough to expect quantum computers in 10 years, but it could be 50 years before we get quantum computers," Laflamme said. "For people working in the field, quantum computers are the holy grail. ... On the way there, there are the side effects: quantum communication and cryptography, the sensors that people are building."

As I explained back in 2000, quantum information processing could be used to crack the secret codes that currently protect confidential information on the Internet. But quantum technology is also well-suited for a new kind of encryption that would instantly detect the presence of eavesdroppers.

"It offers ways of returning to ideas of privacy," said David Cory, a nuclear engineering professor at the Massachusetts Institute of Technology who specializes in spin-based quantum information processing. "There are a lot of appealing ideas to the power of quantum cryptography and quantum communication."

Taming quantum physics
Cory acknowledged that non-scientists can have a hard time with some concepts in the quantum world - for example, the idea that something can be "on" and "off" at the same time. The thought experiment known as "Schrödinger's Cat," in which a cooped-up kitty is considered simultaneously dead and alive, is a classic example of the weirdness surrounding quantum superposition. But Cory also thinks the weirdness is oversold.

"It makes me cringe when I hear people say how weird quantum mechanics is, when we understand it so well," he told me. "The first lesson is that you shouldn't suggest it's so weird. It is wonderfully predictable. You really can do the engineering right."

"And it's a mathematically beautiful field," Zeilinger added. "It's mind-boggling how beautiful it is. Unfortunately, you have to know mathematics to see that. But it's really beautiful."

Zeilinger, Cory and Laflamme all contribute to reducing the weirdness quotient in "The Quantum Tamers," a new video documentary created by Canada's Perimeter Institute for Theoretical Physics. The 52-minute program features easily digestible talks about quantum physics by 19 big-name scientists, with Stephen Hawking as the headliner. You'll also see eye-pleasing demonstrations of superposition, entanglement and teleportation, performed by actors and dancers who stand in for the quantum bits.

O'Connell et al. / Nature
University of Waterloo quantum physicist Ray Laflamme explains superposition
with the aid of a four-armed bearer of ones and zeroes in "The Quantum Tamers."

The show has been scheduled for airing in television markets around the world, but not yet in the United States. DVDs are available for institutional use, but not yet for the home-video market (unless you're up for paying $169.95 plus shipping and tax). I suspect that it's only a matter of time before "The Quantum Tamers" shows up on a TV set near you. In the meantime, you can watch a series of clips from the documentary online.

Laflamme said working on the show was loads of fun - and loads of work. "I seem to set myself up for things that take more time than I thought," he told me. But the way Laflamme sees it, getting out the message about quantum physics is as important as actually doing quantum physics.

"I eat, sleep and think about this all the time," he told me. "I love to try to extract the important pieces of it, and try to explain it. I'm one of those who believes that these technologies will have a profound impact on society. My bet is that it will be the same as the information technologies that we've seen in the past 50 years. ... It will dramatically change the way we think about and perceive the world. It might take 50 or 100 years, but it will happen."

Update for 6:15 p.m. ET March 18: Veteran science writer Charlie Petit, the guru behind the Knight Science Journalism Tracker, offers up the full text of the commentary written by Aspelmeyer. "He could have made a living as a journalist - but may be having as much fun in physics already," Petit says.

Authors of the Nature research on the mechanical resonator include A.D. O'Connell, M. Hofheinz, M. Ansmann, Radoslaw C. Bialczak, M. Lenander, Erik Lucero, M. Neeley, D. Sank, H. Wang, M. Weides, J. Wenner, John M. Martinis and A.N. Cleland, all of the University of California at Santa Barbara. The researchers for the paper on the hybrid quantum system are Christoph Zipkes, Stefan Palzer, Carlo Sias and Michael Köhl, all of the University of Cambridge's Cavendish Laboratory.

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