Entanglement in a three spin system controlled by electric and magnetic field

We show influence of electric field and magnetic flux on spin entanglement in an artificial triangular molecule build of coherently coupled quantum dots. In a subspace of doublet states an explicit relation of concurrence with spin correlation functions and chirality is presented. The electric field modifies super-exchange correlations, shifts many-electron levels (the Stark effect) as well as changes spin correlations. For some specific orientation of the electric field one can observe monogamy, for which one of the spins is separated from two others. Moreover, the Stark effect manifests itself in different spin entanglement for small and strong electric fields. A role of magnetic flux is opposite, it leads to circulation of spin supercurrents and spin delocalization.Comment: 7 pages, 8 figure

Theoretical Studies of Quantum Interference in Electronic Transport Through Carbon Nanotubes

We performed studies of coherent electronic transport through a single walled carbon nanotube. In the calculations multiple scattering on the contacts and interference processes were taken into account. Conductance is a composition of contributions from different channels. We studied also spin--dependent transport in the system with ferromagnetic electrodes. The magnetoresistance is large and shows large oscillations, it can be even negative in some cases.Comment: 6 pages, 4 figures, oral presentation at the XXXI International School on the Physics of Semiconducting Coumpounds, Jaszowiec 2002, to appear in the Acta Physica Polonic

Fano versus Kondo Resonances in a Multilevel "Semi-Open" Quantum Dot

Linear conductance across a large quantum dot via a single level e_0 with large hybridization to the contacts is strongly sensitive to quasi-bound states localized in the dot and weakly coupled to e_0. It oscillates with the gate voltage due to interference of the Fano type. At low temperature and Coulomb blockade, Kondo correlations damp the oscillations on an extended range of gate voltage values, by freezing the occupancy of the e_0 level itself. As a consequence, antiresonances of Fano origin are washed out. The results are in good correspondence with experimental data for a large quantum dot in the semi-open regime.Comment: 4 eps figures, RevTex format, revised version, to appear in Phys. Rev. Letter

Algorithms and Misinformation: The Constitutional Implications of Regulating Microtargeting

The increased popularity of social media in recent years has brought with it unwanted consequences. Most notably, the world is experiencing a widespread epidemic of online misinformation and disinformation. In the form of news stories and advertisements, false information about candidates like Joe Biden, Hillary Clinton, and Donald Trump has spread over Facebook, Instagram, Twitter, and TikTok. Since false information is often more sensational than the truth, this information is reposted and shared until it reaches millions of people. However, the real culprit of this misinformation phenomenon is microtargeting—algorithms that exploit users’ personal information and previous media interactions to target specific posts to individual users. These algorithms send posts to users’ newsfeeds without regard for the credibility of the information, leading users to believe that what they are seeing is true. Further, microtargeting intensifies political party polarization because users are only shown posts with which they already agree. Can the government do anything about this? This Comment examines the extent to which micro targeting can be regulated without exceeding the confines of the First Amendment