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March, 2003 EEEL Demonstrates Single Photon Source |
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Rich Mirin of EEEL's Optoelectronics Division has demonstrated the emission of individual photons on demand, a major accomplishment in the development of "single photonics", which utilizes the photon as the fundamental particle of optical metrology. A low density of InGaAs quantum dots (QDs), semiconductor nanostructures with 10-20 nm dimensions, is grown on GaAs by molecular beam epitaxy. Individual quantum dots are isolated by a mesa etch. A pulsed laser illuminates the QD sample, exciting electron-hole pairs that are captured by the QD. The electron and hole recombine in the QD, emitting exactly one photon that is incident on an intensity interferometer with a 50/50% beamsplitter and photon counting detectors. A histogram of start-stop time intervals is recorded. At time interval zero, there is a very small peak compared to the peaks that are observed at multiples of the excitation laser repetition rate. This is the signature that the photons are emitted one a time (photon on demand). In contrast, when multiple QDs are excited simultaneously, the peak height at a time interval of zero is equal to that at other time intervals corresponding to the laser repetition rate.
Applications of the single photon turnstile are envisioned for the development of high-accuracy, quantum-based radiometry, in which laser power and energy measurements are calibrated by counting photons. Single photon sources are also critical components of quantum cryptography, or quantum key distribution, an ultra-secure form of communication.
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