Quantum Optics Gives RIT’s Physics Program a Big Edge
Course takes students on strange ride through quantum physics
July 15, 2011
by Susan Gawlowicz
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Physics major Robyn Schwartz is getting a jump start on her senior capstone project this summer, and it’s leading her deeper into the quantum world, the realm of molecules, atoms and subatomic particles, where nothing is quite as it seems.
Schwartz, like Alice (in Alice in Wonderland) is ready to go down that rabbit hole, but there’s one hitch: She first needs to brush up on her quantum mechanics.
In the fall, Schwartz will begin, in earnest, her capstone project exploring quantum game theory and its applications with physics professors Edwin Hach III and Gregory Trayling, while taking Quantum Mechanics I from Hach, a lecturer and theoretical physicist specializing in quantum optics.
Schwartz got hooked on physics between her junior and senior years in high school in Merrick, N.Y.
“I did a small theoretical project involving quantum optics, which was on types of entangled quantum states in quantum computers, and so when I found out RIT was offering a class on it as an elective, I took a chance at it,” she says.
The physics department offered the Quantum Optics lecture and corresponding lab as a special topics course for the first time in the spring. To her disappointment, Schwartz was unable to register for the class, not yet having mastered the prerequisite Quantum Mechanics I. Nevertheless, she was allowed to sit in on Hach’s class.
His lecture introduced the four enrolled students—three physics undergraduates and a microsystems graduate student—and a small group of interested scientists and students, including Schwartz, to an aspect of physics typically beyond the scope of an undergraduate program.
Hach’s classroom lectures are only part of the equation. The Quantum Optics lab assignments illustrate the concepts and the stranger side of quantum physics.
“There aren’t many schools that can claim to have a quantum optics lab,” says Hach. “The lab component—ironic, being a theorist—is the crowning jewel of the class.”
Bucknell University, Colgate University and the University of Rochester are among the few that offer quantum optics at the undergraduate level. The subject matter is generally reserved for graduate students for a couple reasons, Hach explains: most undergraduates aren’t ready to tackle the difficult discipline of quantum physics until they are upperclassmen and setting up quantum optics teaching labs is expensive.
“They are looking at—with the third lab—photonic output that is so exotic you need thousands of dollars worth of sensitive equipment,” he says.
Enter Ronald Jodoin, professor emeritus in the College of Science, and Stefan Preble, assistant professor of microsystems engineering and leader of RIT’s Nanophotonics Group. Jodoin, who retried in May after 37 years at RIT, wanted to demonstrate the mind-boggling complexities of quantum optics to undergraduates. He had developed an undergraduate optics lab while on sabbatical at the UR during the previous year. Jodoin knew that RIT could build its own lab by combining resources in the College of Science and the Kate Gleason College of Engineering. He approached Preble to design and co-teach the lab component with him and asked Hach to lecture.
“It was a stroke of luck that Ron and Stefan and I were here at the same time,” says Hach. “It was a perfect storm of research for us.”
Funds to set up the lab came from the physics department and through Preble’s leveraging of Joseph M. Lobozzo II’s donation to the university. Lobozzo, the founder of JML Optical Industries Inc., established RIT’s Lobozzo Photonics and Optical Characterization Laboratory in the College of Engineering.
Quantum optics describes how discrete units of light, or photons, and matter interact on small scales. The subfield of physics grew from quantum mechanics and came into its own with advances in laser science. It represents a philosophical foundation of physics with “rigorously practical applications,” Hach says.
“Quantum mechanics is probably one of the greatest developments of the 20th century,” Preble notes. “It’s an extraordinarily successful theory. So many things rely on it. Computers wouldn’t exist without it. All the understanding of how transistors work would be impossible without quantum mechanics.”
According to the rules of quantum optics, photons can take the form of waves or particles, depending on the experimental set-up and the way in which they are measured. An experiment the students conducted in the spring called the “quantum eraser” explored this idea of wave-particle duality. “If you look at a photon as a wave it will act like a wave; and if you look at it as a particle, it will act like a particle,” Jodoin explains.
“It’s almost as if you’re changing history,” he continues. “You’ve decided after the fact that you want to measure it as a particle or as a wave, and it still behaves as a wave or a particle depending on the way you measure it, so it’s really strange stuff. This is typically stuff to talk about in a quantum mechanics course, but very few places actually do experiments to show it to undergraduates.”
Quantum entanglement, which captured Schwartz’s interest in high school, is a key concept explored in the lab and distinguishes quantum mechanics from classical physics.
“There’s no analogy in the classical world,” Preble says. “When I move this object, it could move this one over here across the entire universe. When I know something about this one, I know something about this other one, even though their properties are random.”
“Classically, you can predict where something is going to go and measure it and it goes there; quantum mechanically, you can only predict the probability that it will go there,” Jodoin says. “You do the experiment many times and the statistical averages agree with the quantum mechanical predictions.”
Some of today’s edgier breakthrough research is attempting to harness the technological possibilities inherent in the entangled states of photons. Research areas like quantum cryptography, quantum computing and quantum teleportation could improve Internet security, lead to massively parallel computing power in which all calculations are processed simultaneously instead of serially, and enhance satellite communications systems.
“This is the future,” Preble says. “Quantum cryptography is going to be a big deal and quantum computation has become bigger over the last couple of years. Because of that we need to make sure our students are experts in that.
“The theory part is to understand how superposition and entanglement comes about, and it’s very rigorous math,” Preble says. “And the lab part is to demonstrate some of those things to the students through basic experiments. We’re not making a quantum computer in the lab, but we’re doing those basic things like entanglement and superposition.”
In one lab assignment, students experimented with polarization entanglement by shooting a laser through a special nonlinear crystal. Eventually, a photon split into perfect twin units of light, each with half the energy of the original and with intertwined or entangled states. The students found that measuring the polarization of one photon will affect the other no matter how far apart they are.
“It is a purely quantum mechanical behavior,” Jodoin says. “Einstein called it ‘spooky action at a distance.’”
Schwartz looks forward to seeing for herself how photons behave in the quantum optics lab. “Someday I will have the opportunity to work on an experimental project in quantum optics,” she says.
The Quantum Optics lecture and lab will run as a pilot again in the spring for students who have completed Quantum Mechanics I. If Quantum Optics proves to be popular and well received, Jodoin, Hach and Preble will propose it as a regularly offered class.
“I would love to see RIT add Quantum Optics to the physics curriculum,” Hach says. “It would put the program in company of only a select few universities that offer it.”
If quantum optics makes it into the physics curriculum, expect to see the recently retired Jodoin back on campus. “There’s a good chance that I’ll come back and do a little adjunct teaching,” he says. “I would like to get back in the quantum lab.”