In a recent theoretical study published in the journal Nanotechnology, researchers from University of Manitoba, Canada, have investigated electron and hole states in a CdTe quantum dot containing a single magnetic impurity in an external magnetic field. They have shown that the s,p-d spin interaction brings about level anti-crossings between the dark and bright exciton states, and have explained the physics behind these anti-crossings. The results are in good agreement with experimental observations.

The scientists also propose a new magneto-optical mechanism for manipulation of the magnetic impurity spin, which involves using laser pulses and varying the strength of the magnetic field. A simplified picture of the proposed mechanism of impurity spin manipulation in a quantum dot is shown schematically in the image above.

Consider (a) a CdTe quantum dot with a single magnetic impurity (Mn atom with spin S=5/2) in the pure state Sz=–5/2, in an external magnetic field near the anti-crossing point. We can (b) excite the system using a laser pulse to create an exciton in the bright state. The electron and hole thus generated will couple with the impurity due to s,p-d spin interactions. A quick sweep of the magnetic field above the anti-crossing point will generate (c) a spin flip of the magnetic impurity to its value Sz=–3/2. Likewise we can go through all the remaining values of the spin projection of the magnetic atom (Sz=–1/2, 1/2, 3/2 and 5/2).

The properties of quantum dots containing a magnetic impurity, as studied in the article in Nanotechnology, have the potential for applications in the rapidly developing field of quantum information processing, in particular for information storage and read-out.

Additional information can be found in the journal.