Recycling Lost Energy: Quantum Laser Turns Energy Loss Into Gain?

 

Exciton-polaritonic PT symmetry: Direct coupling between upward- and downward-polariton modes in a six-fold symmetric microcavity with loss manipulation leads to PT-symmetry breaking with low-threshold phase transition. Credit: KAIST

Researchers at KAIST have invented a laser system that produces highly interactive quantum particles at room temperature. Their discoveries, published in the journal Nature Photonics, could lead to a single microcavity laser system that involves lower threshold energy as its energy loss increases.

 

The system, developed by KAIST scientist Yong-Hoon Cho and colleagues, involves shining light through a particular hexagonal-shaped microcavity treated with a loss-modulated silicon nitride substrate. The system design leads to the generation of a polariton laser at room temperature, which is thrilling because this generally requires cryogenic temperatures.

 

The physicists found another rare and counter-intuitive feature of this design. Generally, energy is lost during laser operation. But in this system, as energy loss increased, the amount of energy required to induce lasing decreased. Exploiting this process could lead to the development of high efficiency, low threshold lasers for upcoming quantum optical devices.

 

“This system relates a concept of quantum physics called parity-time reversal symmetry,” explains Professor Cho. “This is a significant platform that permits energy loss to be used as gain. It can be used to reduce laser threshold energy for standard optical devices and sensors, along with quantum devices and monitoring the direction of light.”

 

The key is the design and materials. The hexagonal microcavity splits light particles into two different modes: one that passes through the upward-facing triangle of the hexagon and the other that passes through its downward-facing triangle. Both types of light particles have the same energy and path but do not interact with each other.

 

Still, the light particles do interact with other particles called excitons, delivered by the hexagonal microcavity, which is made of semiconductors. This interaction causes the generation of new quantum particles called polaritons that then interact with each other to produce the polariton laser. By monitoring the extent of loss between the microcavity and the semiconductor substrate, a fascinating process arises, with the threshold energy becoming smaller as energy loss increases.

Reference:

“Room-temperature polaritonic non-Hermitian system with single microcavity” by Hyun Gyu Song, Minho Choi, Kie Young Woo, Chung Hyun Park and Yong-Hoon Cho, 10 June 2021, Nature Photonics.

https://doi.org/10.1038/s41566-021-00820-z