Researchers from the National Institute of Standards and Technology (NIST) and the Joint Quantum Institute (JQI), a collaborative center of the University of Maryland and NIST, have reported a new way to fine-tune the light coming from quantum dots, by manipulating them with pairs of lasers. The accomplishment could accelerate development of powerful advanced cryptography applications, projected to be a key 21st-century technology.
When energized, a quantum dot emits photons just as a solitary atom does, but imperfections in a quantum dot's shape cause energy levels to separate. This ruins the balance of the ideal state required to emit entangled photons. The NIST-JQI team used lasers to control the energy levels of quantum dots. By adjusting the intensity of the laser beams, they were able to correct for imperfection-caused variations. In doing so, the team was the first to demonstrate that laser-tuned quantum dots can efficiently generate photons one at a time, as required for quantum cryptography and other applications.