Scientists Create A Quasiparticle That Behaves Like It Has Negative Mass

Visual representation of the optical set up that can create the polariton with negative mass. Michael Osadciw/University of Rochester

Researchers have used lasers and a sophisticated optical system to create something we have never seen before, a quasiparticle that behaves like it has negative mass. This discovery could improve both lasers and their applications as well as help us understand better this almost-sci-fi topic.

The object in question is a quasiparticle called a trion-polariton, a peculiar interaction between photons and electromagnetic field produced by certain electron configurations in a semiconductor, another quasiparticle known as an exciton. Quasiparticles behave just like regular particles and they are very useful in forefront physical research. What scientists have observed, as reported in Nature Physics, is a polariton that acts like it has negative mass.

Just to give you a sense of what something with negative mass would do, consider that if you were to pull something towards you, if it had negative mass it would accelerate away from you. (It is not clear, at the moment, if cats are made of negative mass particles.)

“By causing an exciton to give up some of its identity to a photon to create a polariton, we end up with an object that has a negative mass associated with it,” senior author Professor Nick Vamivakas, from Rochester University, said in a statement. “That’s kind of a mind-bending thing to think about because if you try to push or pull it, it will go in the opposite direction from what your intuition would tell you.”

The set-up itself is very interesting. A laser is shot inside an optical microcavity where it is confined. In there, they place a semiconductor that generates the exciton. The exciton then interacts with trapped light to create the polariton. 

Negative mass discussions are often associated with warp drives and wormholes but I’m afraid this won’t help solve either. But it seems like it could be engaged in producing more efficient lasers because it's possible to get light out of the polaritons with a lot less energy than in a regular laser.

“With the polaritons, we’ve created with this device, the prescription for getting a laser to operate is completely different,” Vamivakas explained. “The system starts lasing at a much lower energy input.”

Even more applications of such a peculiar quasiparticle might be on the way, but the team wants to first understand the polaritons' behavior and how to exploit it.

“We’re dreaming up ways to apply pushes and pulls—maybe by applying an electrical field across the device—and then studying how these polaritons move around in the device under application of external force,” Vamivakas concluded.

Negative mass particles might not be there to power your spaceship, but maybe soon they can make our lasers more energy efficient.

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