Breakthrough could pave the way for new quantum technology

Physicists at the University of Chicago have invented a “quantum flute” that, like the Pied Piper, can coerce particles of light into moving together in ways never seen before.

Described in two studies published in Physical examination letters and Natural Physicsthis breakthrough could open the way to the realization of quantum memories or to new forms of error correction in quantum computers, and to the observation of quantum phenomena invisible in nature.

Assoc. Professor David Schuster’s lab is working on quantum bits – the quantum equivalent of a computer bit – which harness the strange properties of particles at the atomic and subatomic level to do things otherwise impossible. In this experiment, they worked with particles of light, called photons, in the microwave spectrum.

The system they imagined consists of a long cavity made from a single block of metal, intended to trap photons at microwave frequencies. The cavity is made by drilling offset holes – like holes in a flute.

“Just like in the musical instrument,” Schuster said, “you can send one or more wavelengths of photons through the whole thing, and each wavelength creates a ‘note’ that can be used to encode quantum information. The researchers can then control the interactions of the “notes” using a master quantum bit, a superconducting electrical circuit.

But their strangest discovery was how photons behaved together.

In nature, photons almost never interact – they just pass through each other. With careful preparation, scientists can sometimes trick two photons into reacting to the presence of the other.

“Here we’re doing something even weirder,” Schuster said. “At first, the photons don’t interact at all, but when the total energy of the system reaches a tipping point, all of a sudden they’re all talking to each other. »

Having so many photons “talking” to each other in a lab experiment is extremely strange, like seeing a cat walk on its hind legs.

“Normally, most particle interactions are one-on-one – two particles bouncing or attracting each other,” Schuster said. “If you add a third, they usually always 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 “notes” at a time, but eventually scientists could imagine running hundreds or thousands of notes through a single qubit to control them. With an operation as complex as a quantum computer, 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 them all through a single bit, this would be incredibly valuable. . »

Researchers are also excited about the behavior itself. No one has observed anything like these interactions in nature, so the researchers also hope the discovery may be useful in simulating complex physical phenomena that cannot even be seen here on Earth, possibly including even part of black hole physics.

Beyond that, the experiments are just fun.

“Normally, quantum interactions take place on time and length scales that are too small or too fast to see. In our system, we can measure single photons in any of our notes and observe the effect of the interaction as it occurs. It’s really great to ‘see a quantum interaction with your eye,’ said UChicago postdoctoral researcher Srivatsan Chakram, the paper’s co-first author, now an assistant professor at Rutgers University.

Graduate student Kevin Il was the article’s other first author. Other co-authors were 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 at the Institute of Semiconductors, Chinese Academy of Sciences); Professor Liang Jiang of the Pritzker School of Molecular Engineering; and visiting scholar Hyeokshin Kwon from 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 produce the devices.

Source of the story:

Materials provided by University of Chicago. Original written by Louise Lerner. Note: Content may be edited for style and length.

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