Credit: David Reilly
Michael Biercuk never heeded advice to avoid sweating the small stuff - in his world of precision metrology, tiny things matter. The forces that interest Biercuk are about a septillion times smaller than the weight of a feather, on the scale of yoctonewtons (that's 10-24 of a Newton, the standard unit of force).
Because forces this tiny can have huge effects on the behavior of electrons in a solid material, being able to measure them precisely is critical to solving much larger problems in nanotechnology, Biercuk says.
That's motivated him to devote a career to worrying about the very small, beginning as a Harvard PhD student, where he studied tiny carbon nanotubes so thin they behave as though they are one-dimensional to the charges that flow through them. Now, as the Director of the Quantum Control Laboratory and a chief investigator in the Australian Research Council Centre of Excellence for Engineered Quantum Systems at the University of Sydney, he's using trapped atomic ions to model (relatively) large and complicated quantum phenomena.
If you've never heard of the prefix yocto, you're not alone. As the smallest measurement prefix that the International System of Units has named, it hasn't gotten much use. Although physicists have known for decades that trapped atomic ions reacted to forces at the yoctoscale, Biercuk, along with then colleagues at the National Institute of Standards and Technology in Colorado, performed the first calibrated measurement of force-detection sensitivity with ions.
In the process the team set a record for the most sensitive measurement of force to date, detecting just a few hundred yoctonewtons with only one second of measurement time. And that notion of 'sensitivity' is key - it allows scientists to make apples-to-apples comparisons between different measurement technologies, taking into account how long it takes to extract information from a sensor.
If Biercuk has his way, 23 zeros will soon be too few. His growing research group at the University of Sydney continues to advance precision measurement with trapped ions. "It's exciting to push the limits of human capability," he says. In his group, researchers can trap and control individual atoms using electromagnetic fields - and those trapped ions can be used for precision force sensing or probing studies of the fundamentals of quantum mechanics.
Most previous force-detection techniques have used an arm-like cantilever that can be perturbed when force is applied, but Biercuk determined that atomic ions could measure forces with one thousand times greater sensitivity. You can think of trapped atoms like marbles in a bowl, he explains. If you tap the marble, it rolls up the side of the bowl before eventually settling back down at the bottom. Ions trapped in an electromagnetic field work similarly - applying a force to an ion will cause it to move, and that "motional response" can be used to detect the force.
Even if scientists aren't interested in forces quite so small, the increased sensitivity of ion-based detectors means that the instruments can make the same measurement about a million times faster than other methods because less time is required to distinguish the interesting force from mere "background noise", Biercuk says.
The ultra-sensitive measurement earned Biercuk a National Measurement Institute Prize for excellence in measurement techniques. But measuring forces with such precision is only a tool to reach his overall goal of using atomic ions to model much more complicated quantum systems: a process called quantum simulation.
Quantum effects come into play in all areas of science - not only in nanotechnology and materials science but also in chemistry and potentially biology. For example, the way chemical compounds react is largely based on the quantum behaviour of their electrons.
But systems like proteins or interacting electrons in a solid are too complex to model using traditional computers. Biercuk says that combining groups of atomic ions and coupling them through their shared motion (ions repel each other because of their charges) can "produce a controlled quantum system that can mimic other quantum mechanical systems we don't understand."
Crucially, understanding even the simplest of quantum systems will require precise knowledge of the way ions react to external forces - right down the yoctonewton.
