Scientists invent a “quantum whistle” that can make light particles move together

Physicists at the University of Chicago have invented a “quantum whistle” that, like the Pied Piper, can force light particles to move together in an unprecedented way.

Described in two studies published in Physical Verification Letters and natural physicsthe breakthrough could point the way to realize quantum memory or new forms of error correction in quantum computers and to observe quantum phenomena that are not visible in nature.

associate Prof David Schuster’s lab is working on quantum bits – the quantum equivalent of a computer bit – that use the strange properties of particles at the atomic and subatomic level to do things that would otherwise be impossible. In this experiment, they worked with light particles, so-called photons, in the microwave spectrum.

The system they developed consists of a long cavity made from a single block of metal designed to capture photons at microwave frequencies. The cavity is made by drilling staggered holes – like holes in a flute.

“Just like with a musical instrument,” Schuster said, “you can send one or more wavelengths of photons across 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” with a master quantum bit, a superconducting circuit.

But their strangest discovery was the way the photons behaved together.

In nature, photons rarely interact – they just go through each other. With careful preparation, scientists can sometimes cause two photons to respond to each other’s presence.

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

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

“Typically, most particle interactions are one-to-one — two particles rebounding or attracting each other,” Schuster said. “If you add a third, they usually still interact with one or the other in sequence. But with this system, they all interact at the same time.”

Their experiments only tested up to five “notes” at a time, but eventually scientists could envision running hundreds or thousands of notes through a single qubit to control them. With an operation as complex as that of a quantum computer, engineers want to simplify everything where they can, Schuster said: “If you wanted to build a quantum computer with 1,000 bits and could control them all through a single bit, that would be incredibly valuable.” “

The researchers are also enthusiastic about the behavior itself. Nobody has observed anything like these interactions in nature, so researchers hope the discovery may also be useful in simulating complex physical phenomena that can’t even be seen here on Earth, including perhaps even some physics from black holes.

In addition, the experiments are simply fun.

“Typically, quantum interactions take place over length and time scales that are too small or too fast to see. In our system, we can measure individual photons in each of our notes and observe the effect of the interaction as it happens. It’s actually quite nice to ‘ see a quantum interaction with your eye,'” said UChicago postdoc Srivatsan Chakram, the paper’s co-first author, now an assistant professor at Rutgers University.

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