‘Quantum flute’ can make photons move together
Consisting of a long cavity made in a single block of metal, the system is designed to trap photons at microwave frequencies. The cavity is made by drilling offset holes – like those in a flute.
The breakthrough, say the researchers, could point the way towards realizing quantum memories or new forms of error correction in quantum computers, and observing quantum phenomena that cannot be seen in nature.
“Just like in the musical instrument,” says Associate Professor David Schuster, “you can send one or several 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” using a master quantum bit – a superconducting electrical circuit. However, say the researchers, their oddest discovery was the way the photons behaved together.
In nature, photons hardly ever interact —they simply pass through each other. With painstaking preparation, say the researchers, scientists can sometimes prompt two photons to react to each other’s presence.
“Here we do something even weirder,” says Schuster. “At first the photons don’t interact at all, but when the total energy in the system reaches a tipping point, all of a sudden, they’re all talking to each other.”
To have so many photons “talking” to one another in a lab experiment, say the researchers, is extremely strange – akin to seeing a cat walking on hind legs.
“Normally, most particle interactions are one-on-one—two particles bouncing or attracting each other,” says Schuster. “If you add a third, they’re usually still interacting sequentially with one or the other. But this system has them all interacting at the same time.”
In their experiments the researchers only tested up to five “notes” at a time, but say they could eventually 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 everywhere they can, says Schuster:
“If you wanted to build a quantum computer with 1,000 bits and you could control all of them through a single bit, that would be incredibly valuable.”
The researchers say they are also excited about the behavior itself. No one has observed anything like these interactions in nature, so they also hope the discovery can be useful for simulating complex physical phenomena that can’t even be seen here on Earth, including perhaps even some of the physics of black holes.
Beyond that, say the researchers, the experiments are just fun.
“Normally quantum interactions take place over length and time scales too small or fast to see,” says UChicago postdoctoral researcher Srivatsan Chakram, the co-first author of a paper on the research, now an assistant professor at Rutgers University. “In our system, we can measure single photons in any of our notes, and watch the effect of the interaction as it happens. It’s really quite neat to ‘see’ a quantum interaction with your eye.”
For more, see “Multimode photon blockade.”
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