The University of Illinois at Urbana-Champaign has begun to build a strong team of quantum researchers. One of the rising stars in the area is CSL Associate Professor Eric Chitambar, whose research into quantum information science is working to further develop the theory of quantum resources for information processing.
In quantum systems, matter behaves differently than in classical systems. If a tennis ball is bounced in a normal environment, an observer can easily determine its position and momentum throughout the entire process of the bounce. If a similar exercise was tried with an electron or some other very small particle, its position and momentum could not be simultaneously determined. This is because such objects can behave both like a particle and a wave, a hallmark of quantum systems known as wave-particle duality. The potential applications for this combination is the focus of Chitambar’s latest research.
“Is there any utility to this? That’s the question that I study from a communications perspective,” said Chitambar, an associate professor in electrical and computer engineering. “How can we use this wave-like matter to encode information in new beneficial ways, such as increasing the accessibility or security of that information?”
Quantum systems can demonstrate a number of counter-intuitive effects that are not observed in classical systems. Normally, the order of learning information about an object doesn’t matter, such as first figuring out the color and then the fabric of a random sock drawn from a dresser drawer versus figuring out the fabric and then the color. However, the same is not true when dealing with quantum systems. For example, since the position and momentum of an electron cannot be simultaneously known, the order in which these properties are measured can change their outcome: a position measurement followed by a momentum measurement will generally lead to different results than if instead momentum was measured first followed by position. Quantum measurements having this sequential dependence are called incompatible.
“This concept has been known since the origin of quantum mechanics,” said Chitambar. “What we’ve recently gotten interested in is developing a full theory of incompatibility that can be used in verifying the quantumness of some physical process.”
Chitambar and his team have developed a game to test for incompatibility. In the game, there are two players, one that asks questions, and one that answers questions using a black box, which is an abstraction of the quantum measurement process. The second participant must probe the black box in different ways to get answers, and if the box can implement incompatible measurements, the answers are correct and the participant wins the game.
“A sequence of incompatible moves can be constructed to result in a higher score than if you had compatible or classical measurements,” said Chitambar. “This notion of incompatibility is set as a game, and there’s a practical use for it. If you play the game using some untrusted measurement apparatus constructed in a laboratory and you obtain a winning score, then you know your apparatus is demonstrating genuine quantum effects that has no classical simulation.”
The utility of measurement incompatibility researched by Chitambar was discussed in a paper published recently in Physical Review Letters. His group hopes to continue this research as part of the university’s growing portfolio of quantum research.