Researchers Detect Roots of Superfluorescent Bursts from Quantum Wells
2 December 2013
In a study examining spontaneous bursts of light from a solid-state stack of quantum wells, scientists from the Rice University lab of Junichiro Kono, Florida State University and Texas A&M University have found that these flashes, which exist just trillionths of a second, change color as they pulse from within the block. The discovery could pave the way for the development of new telecommunications equipment and other devices that send signals at picosecond speeds.
The phenomenon could be explained as a combination of two many-body concepts established earlier, namely superfluorescence, as detected in atomic and molecular systems, and Fermi-edge singularities, a process known to take place in metals.
Unlike the researchers' first observations of superfluorescence in a solid block, which required exciting semiconductor quantum wells in high magnetic fields, this time no powerful magnets were needed.
At the core of the Fermi-edge superfluorescence process are the semiconducting quantum wells, which contain a dense collection of electrons and holes, confined to move only within the two dimensions allowed by the small, stacked wells, where they undergo strong Coulomb interactions.
The researchers tried to keep the particles as dense as possible at liquid helium temperatures (around -450 degrees Fahrenheit) to ensure that their quantum states are obvious, or "quantum degenerate," which occurs when the so-called Fermi energy is greater than the thermal energy. When pumped by a strong laser, the quantum degenerate particles produced energy and emitted it as light at the Fermi edge. As a result of electrons and holes' combination to release photons, the edge shifted to low-energy particles to initiate more reactions until the sequence played out. As the burst progressed, the released light shifted toward the higher red wavelengths, the researchers established.