Physicists from the University of Chicago have created a “quantum flute” that, like the Pied Piper, can tickle light particles to move together in a never-before-seen manner.
The breakthrough, which was described in two studies published in Physical Review Letters and Nature Physics, could pave the way for the development of quantum memories and new forms of error correction in quantum computers, as well as the observation of quantum phenomena that cannot be observed in nature.
The lab of associate professor David Schuster focuses on quantum bits, the quantum counterpart of a computer bit, which utilise the peculiar properties of subatomic and atomic particles to do otherwise impossible tasks. In this experiment, photons, also known as light particles, were utilised in the microwave range.
The apparatus they invented consists of a metal block with a large hollow designed to trap photons at microwave frequencies. The cavity is created by drilling offset holes, similar to flute holes.
“Just as in a musical instrument,” Schuster explained, “you may send a single or several wavelengths of photons across the entire structure, and each wavelength produces a ‘note’ that can be utilised to encode quantum information.” The researchers can then control the interactions of the “notes” using a superconducting electrical circuit containing a master quantum bit.
The most peculiar discovery, however, was the collective behaviour of photons.
Photons rarely interact in nature; they just flow through one another. Scientists can sometimes induce two photons to react to each other’s presence through meticulous preparation.
“Here we do something even weirder,” Schuster stated. “Initially, the photons do not interact with one another, but when the overall energy in the system hits a tipping point, they all start chatting to one another.”
Observing that many photons “talking” to one another in a laboratory experiment is as bizarre as witnessing a cat walk on its hind legs.
“In general, the vast majority of particle interactions are one-on-one — two particles bouncing or attracting one other,” Schuster explained. “Typically, when you add a third, they continue to interact sequentially with one or the other. However, this system has them all interacting simultaneously.”
Their research only examined up to five “notes” at a time, but the scientists can envision potentially controlling hundreds or thousands of notes with a single qubit. With a system as complex as a quantum computer, engineers strive to simplify wherever possible. Schuster stated, “If you wanted to construct a quantum computer with 1,000 bits and could control them all with a single bit, that would be tremendously valuable.”
Additionally, the researchers are enthusiastic about the behaviour itself. These interactions have never been observed in nature, therefore the researchers believe that the discovery can be used to simulate complex scientific events that cannot even be observed on Earth, such as the physics of black holes.
Beyond this, the experiments are simply enjoyable.
“Typically, quantum interactions occur on length and temporal scales that are too small or quick to observe. In our technology, we can monitor individual photons in any of our notes and observe the interaction in real time. It is pretty fascinating to’see’ a quantum interaction with the naked eye “Srivatsan Chakram, a postdoctoral researcher at the University of Chicago and currently an assistant professor at Rutgers University, is the co-first author of the work.
Graduate student Kevin He was the second author listed on the publication. Other co-authors included graduate students Akash Dixit and Andrew Oriani; former UChicago students Ravi K. Naik (now at UC Berkeley) and Nelson Leung (now with Radix Trading); postdoctoral researcher Wen-Long Ma (now with the Institute of Semiconductors at the Chinese Academy of Sciences); Professor Liang Jiang of the Pritzker School of Molecular Engineering; and visiting researcher Hyeokshin Kwon of the Samsung Advanced Institute of Science and
Schuster is affiliated with both the James Franck Institute and Pritzker School of Molecular Engineering. The gadgets were manufactured at the University of Chicago’s Pritzker Nanofabrication Facility.