Although qubits have been made with trapped photons, atoms and ions, it is generally thought that it should be easier to build working devices with solid-state systems. Several teams have made significant progress with the superconducting approach to solid-state quantum computing. Now Steel and co-workers at Michigan, Michigan State, the Naval Research Laboratory and the University of California at San Diego have demonstrated the first all-optical quantum gate in a semiconductor quantum dot. Steel and co-workers grew a thin gallium arsenide layer 4.2 nm thick between two 25 nm aluminium gallium arsenide barriers to make a quantum dot. Electrons are trapped in the dot because the gallium arsenide layer has a smaller energy band-gap than the surrounding material. When excited by light, electrons from the valence band in the dot move to higher energy levels. The excited electron and the hole it leaves behind combine to form an exciton. The system has four states: a ground state containing two unexcited electrons; two states containing one exciton; and a state containing two excitons (see figure). The two single-exciton states can be distinguished from each other because the excitons have different polarizations.
http://physicsweb.org/article/news/7/8/5
Sunday, August 10, 2003
Popular Posts
-
http://www.homestarrunner.com/sbemail94.html
-
...why was this given the file name of skyfall?... Certain information, while not specific as to target, gives the government reason to beli...
-
The concept of dragons was probably brought to Japan around 2,000 years ago, along with the technology for paddy agriculture. Their images h...
-
Some good stuff from a Canadian futurist: - The rising power of the knowledge worker - Continuous training replaces job security; respect is...
-
Very dry, dull book with some basic financial info like ROI and cash flow. Not a lot here.
-
Not a bad audio book, but I expected more. Big ideas: Build a high performance, high-trust culture; Identify desired results and un...
-
Someone that gets it. Service-oriented software, when done correctly in a platform-agnostic way can be flexible, cheap, and can motivate m...
-
http://esamultimedia.esa.int/images/marsexpress/377-260208-2149-6-co-01-HebesChasma_H1.jpg
-
Peruvian archeologists have discovered the first full Inca burial site at Machu Picchu since the famous mountaintop citadel was discovered 9...
-
For the first time, Europe has more internet users than the US. According to Irish-based industry monitor Nua.com, Europe has almost 186 mil...