Detecting dangerous chemicals with lasers, exploring the brain's circuitry with light and more

The exchange of information between distant sources is the basis of all communications, but quantum mechanics may open up this distant exchange as never before. Quantum key distribution, for instance, would allow for absolutely secure encryption of information exchange by encoding information keys on single photons. These photons are so sensitive that there is physically no way to undetectably tamper with them as they travel from sender to receiver. Teleportation of quantized states is another possible application. This would allow future quantum computers to be interconnected using the properties of individualized photons or other quanta.

To achieve this type of technology, an exchange of single quanta between a sender and a remote receiver must occur. Already, some companies have explored ways of achieving quantum key distribution over fiber optics, but it has never been done using satellites. Paolo Villoresi and his colleagues at the University of Padova in Italy, in collaboration with the group of Anton Zeilinger in Austria, have taken the first step to establishing quantum communications in space by exchanging single photons from an orbiting satellite to Earth. They demonstrated how the Matera Laser Ranging Observatory in Matera, Italy, used for satellite laser ranging with ultimate precision, can be adapted as a quantum communication receiver to detect single quanta emitted by an orbiting source—in this case a Japanese low-Earth-orbiting satellite. They also identified the exact techniques needed to detect the very weak quantum signal to be exploited in a dedicated satellite. (Talk QWB3, "Experimental Study of a Quantum Channel from a LEO Satellite to the Earth.")

PHOTOLUMINESCENCE IN NANO-NEEDLES

Silicon is the workhorse among semiconductors in electronics. But in opto-electronics, where light signals are processed along with electronic signals, a semiconductor that is capable of emitting light is needed, which silicon can't do very well. Here gallium-arsenide (GaAs) is the workhorse, especially in the creation of light emitting diodes (LED) and LED lasers.

Scientists at the University of California, Berkeley have now grown GaAs structures into the shape of narrow needles which, when optically pumped, emit light with high brightness. The needles are approximately 3 to 4 microns long and taper at an angle of 6 to 9 degrees down to tips approximately 2 to 5 nanometers across. These needles are not yet lasers; creating them will be the next step. This represents the first time a lab has been able to fashion GaAs into a defect-free crystal structure (technical name: wurtzite) exactly like this on a silicon substrate and without the use of catalysts.