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

A new “quantum flute” experiment by University of Chicago physicists could point the way to new quantum technologies. The holes create different wavelengths, similar to the ‘notes’ on a flute, that can be used to encode quantum information. Credit: Photo courtesy of the Schuster laboratorium laboratory

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 Letter and Natural PhysicsSuch breakthroughs could point the way to realizing quantum memory or new forms of error correction in quantum computers, and observing 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 the 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. The cavities are made by drilling offset holes—like the 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 by 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-on-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.

“Typically quantum interactions take place on 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 as it occurs. It’s really pretty neat to look at.” ‘quantum interactions with your eyes,’ said UChicago postdoctoral researcher Srivatsan Chakram, co-first author on the paper, now an assistant professor at Rutgers University.

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Twin photons from different quantum dots

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Further information:
Srivatsan Chakram et al, Seamless High-Q Microwave Cavity for Quantum Electrodynamics of Multimode Circuits, Physical Review Letter (2021). DOI: 10.103/PhysRevLett.127.107701

Srivatsan Chakram et al, Multimode photon blockade, Natural Physics (2022). DOI: 10.1038/s41567-022-01630-y

Provided by the University of Chicago

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