Improved Stability of Electron Spins in Qubits

Calculation with electron spins in a quantum computer assumes that the spin states last for a sufficient period of time. Physicists at the University of Basel and the Swiss Nanoscience Institute have now demonstrated that electron exchange in quantum dots fundamentally limits the stability of this information. Control of this exchange process paves the way for further progress in the coherence of the fragile quantum states. The report from the Basel-based researchers appears in the scientific journal Physical Review Letters. (Mehr in: Pressemitteilungen – idw – Informationsdienst Wissenschaft)

Quantum Teleportation and Von Neumann Entropy

From the aspect of the quantum information theories, various quantum entropies are possibly computed at each stage, which ensures the emergence of the entangled states in the intermediate step. If a single qubit quantum teleportation is near the computational basis, the quantum measurement is dominantly responsible for the joint entropy at the final stage. If it is far from the computational basis, this dominant responsibility is moved into the quantum measurement of system. Therefore, the relative entropy can be regarded as a measure for distance between two different quantum states like trace distance or fidelity. Some relative entropies become infinity, which indicates the non-trivial intersection of the support of one quantum state with kernel of the other quantum state.

You Hwan Ju, Eylee Jung1, Mi-Ra Hwang, D. K. Park, Hungsoo Kim, Min-Soo Kim, Jin-Woo Son, Sahng-Kyoon Yoo, S. Tamaryan (2007) Quantum Teleportation and Von Neumann Entropy. arXiv:0707.1227v1