Reading out quantum information with the laser
One of the main difficulties in developing quantum computers is extracting the valuable information without disturbing the system too much. Engineers around David Awschalom from the University of California in Santa Barbara have now presented a method that evaluates the changed polarization of laser light. The properties of the quanta are apparently hardly affected.
The special feature of quantum computers is that their information-carrying and processing units do not have to assume different states one after the other, but can exist in all of them at the same time. For processes that have to perform the same steps many times with different initial data, this would mean an enormous speed advantage. However, this superposition of the states is very susceptible to disturbances from the environment. Even a simple measurement allows the system to collapse from diversity into a single state. A large part of the result would be lost.
The researchers in California believe they can prevent this by putting the information in the spin of a single electron and storing it on a storage device called a quantum dot. If you illuminate this quantum dot with weak laser light, the polarization of the light is changed slightly, but measurably, according to the Kerr effect. At the same time, however, the superposition state of the electron is preserved.
The discovery is primarily a proof of principle, but can also be used to study quantum dots. A practical application or even a real quantum computer is hardly any closer. (of)
