After five years of graduate school finding ways to capture particles in a vacuum, Brian D’Urso swore off making these sorts of traps. But the ability of those traps to detect tiny forces — and the possibility of what that could achieve — stayed in his mind. 

Now a professor at Montana State University, D’Urso’s research again focuses on “levitated optomechanics” — designing and building ways to use electricity, magnetism and even light to levitate a single particle inside a vacuum. The particles are 1-100 microns across — a micron being a millionth of a meter. This means the largest particles D’Urso works with have diameters roughly equal to the thickness of a sheet of copy paper.

“These traps are beautiful experiments,” D’Urso said. “You can make everything so close to perfect, so close to being so totally controlled. It really behaves the way physics tells you it should behave, so then you can sprinkle in more extra complicated stuff that you don’t understand and see what it does.”

D’Urso, an associate professor in the Department of Physics in the College of Letters and Science will present “Trapping Schrödinger’s Cat: Gravity, Levitation and Quantum Mechanics” as part of the annual Provost’s Distinguished Lecturer Series on Tuesday, Nov. 16, in the Museum of the Rockies’ Hagar Auditorium. The lecture is free and open to the public. A reception will follow.

The lecture will explore the evolution of D’Urso’s research toward testing the paradox of Schrödinger's Cat, a thought experiment created by Erwin Schrödinger in 1935. It takes principals of quantum mechanics — the physics used to describe the movement of atomic or subatomic particles — to the extreme.

One principal, quantum superposition, says that a particle may exist in two or more places, or states. Until that particle is viewed, there is no way to tell which state it’s in. According to D’Urso, superposition is one of many qualities that gives quantum mechanics a spooky reputation.

“Despite this weirdness, the reality is that quantum mechanics works incredibly well, and there are all these things in our daily life, these technologies that we wouldn’t have without the theory,” he said, throwing out atomic clocks, solar panels and global positioning systems as examples.

D’Urso’s three-pronged experimental approach surrounds an idea that would revolutionize detection of gravitational forces, both the “little g” force of Earth’s gravity and the “big G,” Newton’s gravitational constant that describes the attraction of two objects based on their mass and distance from each other. One experiment, currently being redesigned and rebuilt, will use the trap to measure the strength of “big G.”

“This is the most poorly measured fundamental constant in physics,” D’Urso said. “The measurements that have been made aren’t very precise, for one, and secondly, they don’t agree with each other very well.”

Experiments with levitated particles may lead the way to better measurements.

“If you can control most of it, then you can inject in one thing you don’t know that you’re trying to test such as ‘What is G?’ or ‘How does quantum mechanics behave?’” D’Urso said. “You can really clearly get a signature for what is happening in that one thing you don’t know.”

The second and longest-running experiment in D’Urso’s lab in MSU’s Barnard Hall is seeking to measure the position of a tiny glass sphere within the trap as precisely as possible and to slow down its movement. However, interference as slight as photons of light used in the measurement can change the particle’s momentum. A portion of the experiment is even dedicated to pushing the sphere around in the vacuum with lasers.

The experiment is also testing the limits of quantum mechanics. At 1.2 microns across, the glass spheres might turn out to be some of the largest objects to which the quantum mechanics can be applied.

“As you try to apply quantum mechanics to bigger and bigger things, it seems non-sensical,” D’Urso explained. “Thus you get to Schrödinger’s Cat. The cat is both dead and alive. It doesn’t make any sense. We don’t know where quantum mechanics goes from working to maybe not working.”

Rather than glass, or silica, the third experiment uses a particle of silicon carbide, which is known to behave quantum mechanically because a defect in its structure gives it an extra electron that has an associated spin. Within a magnetic trap, D’Urso can study the particle’s spin with spectroscopy and use it to improve the trap’s sensitivity and the measurement of “big G.”

The three experiments build toward D’Urso’s long-term goal to build a tabletop device so sensitive it can detect gravitational waves — ripples in the curvature of space time caused by extreme gravity events such as the collision of neutron stars hundreds of millions of light years from Earth.

This line of experimentation “not only is useful for learning about gravity, learning about gravitational waves, but also for pushing the limits of quantum mechanics,” D’Urso said. “What happens when you have gravity and quantum mechanics combined? That’s really what this kind of system would be.”

The Provost’s Distinguished Lecturer Series features free, public talks that recognize outstanding MSU faculty for their creative scholarship and leadership. Faculty presenting in the series speak on the inspirations for their work in talks aimed at both professionals and the public.