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Breakthrough of the Year: Bridging the Quantum and the Classical Worlds

(Credit: Aaron D. O'Connell and Andrew N. Cleland/University of California, Santa Barbara)

Quantum mechanics lays out a set of mind-bending rules on how very small things move and behave, such as their ability to absorb energy only in discrete amounts (or quanta) and be in two different states at the same time. Although, so far, quantum effects have been observed primarily in molecules, atoms, and subatomic particles, physicists have been putting much effort into observing quantum mechanics in systems closer to human scale. Such efforts are starting to pay off.

"I remember going outside and walking around and thinking, like, ... 'Is this actually happening, or am I just dreaming this? Because I've been trying to do this one thing for 3 years now.' " -- Aaron O'Connell

Working with Andrew Cleland and John Martinis at the University of California (UC), Santa Barbara, earlier this year, Ph.D. student Aaron O'Connell became the first person to experimentally induce and measure quantum effect in the motion of a humanmade object. The work, which was released in March, was voted by Science and AAAS (the publisher of Science Careers) as the 2010 Breakthrough of the Year "in recognition of the conceptual ground their experiment breaks, the ingenuity behind it and its many potential applications," according to a AAAS press release.

But there's more unusual about O'Connell than just his science. His background, value system, and career aspirations are atypical of the scientific community. Despite his remarkable early success, O'Connell is planning to leave physics.

A liberal arts mind

As a high school student, O'Connell focused on everything but science. "I read philosophy. I liked music and arts. I played guitar -- the normal liberal arts things -- and I meshed with those type[s] of people," O'Connell says. Even so, science marked him via a physics teacher who did "crazy things like [shooting] a stuffed monkey to demonstrate how things fall in gravitational fields," O'Connell recalls. (A video of a similar experiment, from the Massachusetts Institute of Technology, is on YouTube.)

Aaron O'Connell. (Credit: Courtesy of Jennifer Dewalt)

In 2001, after a year spent exploring the world, O'Connell entered Eckerd College, a private liberal arts school in St. Petersburg, Florida. He planned to pursue his interest in the humanities. But once he got there, influenced by memories of falling monkeys and pragmatic considerations like better job prospects, he decided to study physics and math.

While he was in college, O'Connell had a series of formative summer research experiences. After his first year, one of his professors paid him to redesign a carbon-clustering apparatus. It "was a really neat experience because I was basically thrown into a lab, had no idea what I was doing, and just told to make stuff happen," he says. He got the apparatus to work by studying thousand-page manuals. "The rest of the time, I was just having fun experimenting with things."

Another of his professors got O'Connell into NASA's Goddard Space Flight Centerin Greenbelt, Maryland, for an internship the following summer. The experience showed him what real research was like, O'Connell says, but it didn't leave much room for creativity. O'Connell's job was to feed a known signal into a device designed to measure greenhouse gases in the atmosphere to see if it behaved as expected. It was, he says, "kind of boring."

Before his senior year, O'Connell did a summer internship with John Goodkind at UC San Diego that got him hooked on quantum physics. The lab was small, O'Connell says, and he was given an important role. "Their expertise was in low-temperature liquid helium physics, so they were trying to build a quantum computer by floating single electrons on top of a bath of liquid helium and manipulating those single electrons," O'Connell says.

These experiences -- especially the last one -- provoked him to pursue a Ph.D. in quantum physics. It was science, but it was also, in a sense, in keeping with his earlier interest in philosophy.

A mind-bending science

O'Connell found his first year of courses as a Ph.D. student at UC Santa Barbara difficult. "The education I received in the liberal arts school was great because it taught me ... how to think like a physicist, but it didn't teach me all the technical details," he says. He worked hard to catch up.

Read more online about Science's Breakthrough of the Year.

After a year and a half spent on another project, O'Connell started working to measure quantum effects in the motion of a humanmade object. "Quantum mechanics makes certain predictions" about how things move and behave "that we don't normally see in the regular world," he says. "One of the main points of the experiment was to take something that is familiar, like where a large thing is in space, and show that quantum mechanics applies to large things as well as the microscopic world." Cleland, Martinis, and collaborators already had laid out the experiment in theory; O'Connell's job was to figure out the specific design and make it work.

The experiment required three things: a special kind of vibrating widget, or "micromechanical resonator," an extremely sensitive measurement device, and specific conditions in which to place them. O'Connell started by microfabricating the resonator on a wafer of silicon, based on resonators developed by the company Agilent for use in mobile phones. The resonator was an aluminum nitride–containing structure that could dilate and contract at the very high frequency of 6 GHz. The resonator had to be isolated by mechanical suspension, which required "developing an in-house capability ... we did not have at all prior to this development," Cleland writes in an e-mail to Science Careers. "This was a remarkable achievement."

The resonator done, O'Connell moved on to the measurement device, which had to be built on the same substrate. He used a quantum electrical circuit Martinis had already developed -- a Josephson phase quantum bit (qubit) -- for quantum computation. The resonator and detector were electrically connected, which added steps to the microfabrication process. The fabrication was "quite challenging because the mechanical resonators are essentially three-dimensional structures ... and qubits are wires on silicon chips, and they're very flat," O'Connell says.

Aluminium nitride is a piezoelectric material, so the mechanical motions would generate electrical signals that could be detected by the qubits. But to observe any quantum effects, the whole chip had to be cooled to a temperature so low that the resonator would occupy its lowest energy state (the quantum ground state of motion).

O'Connell and his colleagues used the qubit to demonstrate that they had reached the true quantum ground state of motion for the first time. Then, by controlling the qubit with an external magnetic flux, they were able to inject individual mechanical quanta into the resonator, the first step toward the quantum control of a mechanical system.

"As soon as I was able to connect the mechanical resonators to a qubit in a reliable way, we measured the sample and it all worked," O'Connell says. The resonator behaved exactly as predicted by quantum mechanics. "Some of these things are very strange, like when you measure it, half the time it's over in one place and half the time it's randomly in the other place, and it's not in the middle."

The work was published online in Nature in March this year. O'Connell was the first author.

Feeling a disconnect

O'Connell possesses a particular package of scientific strengths, Cleland writes, that were crucial to the project's success: intelligence, the ability to learn and focus, and natural equanimity in the face of challenges. "He had far fewer 'roadblock' situations that are common in graduate school. ... He seemed to either solve these situations without the need for advice or would have enough objectivity to recognize the magnitude of the problem and go ask people what they would recommend. While Aaron learned a great deal of technique in graduate school, his maturation seemed to have already occurred prior to this experience."

Realizing he'd succeeded was "a pretty good feeling," O'Connell says. "I remember going outside and walking around and thinking, like, ... 'Is this actually happening, or am I just dreaming this? Because I've been trying to do this one thing for 3 years now.' " The work won accolades from the scientific community and notice in scientific media.

Nevertheless, the experience made O'Connell feel that his needs and expectations were perhaps better aligned with the liberal arts world than with physics. He was eager to also share his results with the general public, but he found it easier to bring together the classical and the quantum worlds than to connect laypeople and physicists. "At the bars, when I talk to people, no one's ever said, 'Oh yeah, I know who you are,' or, 'That thing that you're talking about is interesting.' "

"If more people shared my enthusiasm for what I'm doing, I would more likely continue on in the sciences," says O'Connell, who defended his thesis last week. But "it's hard to keep telling yourself that what you're doing is important when everybody you talk to seems to think what you're doing is not important." Besides, "all the rewards you get as a grad student and a postdoc ... are [in] knowing that you've done something that no one else has done, or ... a select few in the physics community telling you you did a good job, and that doesn't happen very often," he adds. So "I think I am going to go to finance, because at least they compensate you monetarily there."

Like many other Ph.D. students, O'Connell dropped hobbies and lost friends to spend more time on the project. But that's a sacrifice he didn't mind making. "If I wouldn't have been challenged in physics, ... then I would have definitely missed out on something because I feel really well prepared for the rest of the world," he says. Also, had he gone to finance right away, "I might ... be sitting on Wall Street thinking, 'Well, I should have been a physicist because I could have done really cool stuff.' "

Elisabeth Pain is contributing editor for South Europe.

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