Researchers discover 'quantum flute' that can make light particles move together

University of Chicago physicists have discovered a “quantum flute” that, like the Pied Piper, can force light particles to move together in a way never seen before.

Described in two studies published in Physical Review Letters and Nature Physics, the breakthrough could point the way to the realization of quantum memory or new forms of error correction in quantum computers, and to observe quantum phenomena that cannot be seen in nature.

Laboratory Association Prof. David Schuster is working on quantum bits – the quantum equivalent of computer bits – that take advantage of the peculiar properties of particles at the atomic and sub-atomic level to do things that would otherwise be impossible. In this experiment, they worked with light particles, known as photons, in the microwave spectrum.

Their system consists of long cavities built into a metal block, designed to trap photons at microwave frequencies. Cavities are created by drilling offset holes — like holes in a flute.

“Just like in a musical instrument,” says Schuster, “you can send one or more wavelengths of photons across an object, and each wavelength creates a ‘note’ that can be used to encode quantum information.” The researchers were then able to control the interactions of the “records” using the master quantum bits, superconducting electrical circuits.

But their strangest discovery was the way photons behave together.

In nature, photons almost never interact — they just pass through each other. With painstaking preparation, scientists can sometimes induce two photons to react to each other’s presence.

“We’re doing something even weirder here,” said Schuster. “At first the photons didn’t interact at all, but when the total energy in the system reached a critical point, suddenly, they were all talking to each other.”

Having so many photons “talk” to each other in a laboratory experiment is very strange, akin to seeing a cat walk on its hind legs.

“Typically, most particle interactions are one-to-one — two particles bouncing off or attracting each other,” says Schuster. “If you add a third, they usually still interact sequentially with one or the other. But this system makes them all interact at the same time.”

Their experiments only tested up to five “tones” at a time, but scientists were eventually able to imagine running hundreds or thousands of notes through a single qubit to control them. With operations as complex as quantum computers, engineers want to simplify wherever they can, Schuster said: “If you wanted to build a quantum computer with 1,000 bits and you could control everything through one bit, that would be very valuable. .”

Researchers are also passionate about the behavior itself. No one has observed this kind of interaction in nature, so the researchers also hope this discovery can be useful for simulating complex physical phenomena that cannot even be seen on Earth, including perhaps some black hole physics.

Other than that, experimentation is just fun.

“Usually quantum interactions take place over long and time scales that are too small or fast to see. In our system, we can measure a single photon in one of our records, and see the effect of the interaction that occurs. It’s really pretty neat to ‘see’ quantum interactions with your eye,” said UChicago postdoctoral researcher Srivatsan Chakram, co-first author on the paper, now an assistant professor at Rutgers University.

Graduate student Kevin He is another first author on the paper. Other co-authors are 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); Liang Jiang of the Pritzker School of Molecular Engineering; and visiting researcher Hyeokshin Kwon of the Samsung Advanced Institute of Technology in South Korea.

Schuster is a member of the James Franck Institute and the Pritzker School of Molecular Engineering. The researchers used the Pritzker Nanofabrication Facility at the University of Chicago to manufacture the device.

Reference:

1. Srivatsan Chakram, Kevin He, Akash V. Dixit, Andrew E. Oriani, Ravi K. Naik, Nelson Leung, Hyeokshin Kwon, Wen-Long Ma, Liang Jiang, David I Schuster. Multimode photon blockade. Natural Physics, 2022; DOI: 10.1038/s41567-022-01630-y
2. Srivatsan Chakram, Andrew E. Oriani, Ravi K. Naik, Akash V. Dixit, Kevin He, Ankur Agrawal, Hyeokshin Kwon, David I. Schuster. Seamless High-Q Microwave Cavity for Quantum Electrodynamics of Multimode Circuits. Physical Review Letter, 2021; 127 (10) DOI: 10.103/PhysRevLett.127.107701

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